To investigate the protective effects of magnolol on sepsis-induced inflammation and intestinal d... more To investigate the protective effects of magnolol on sepsis-induced inflammation and intestinal dysmotility.
The structures, ionization potentials (IPs), electron affinities (EAs), and HOMO-LUMO gaps (∆ H-L... more The structures, ionization potentials (IPs), electron affinities (EAs), and HOMO-LUMO gaps (∆ H-L) of the oligomers are studied by the density functional theory with B3LYP functional. The lowest excitation energies (Egs) and the maximal absorption wavelength λabs of oligomers of polyfluorene (PF) and poly(2,7-fluorene-alt-co-5,7-dihydrodibenz[c,e]oxepin) (PFDBO) are studied employing the timedependent density functional theory (TD-DFT) and ZINDO. Band gaps and effective conjugation lengths of the corresponding polymers were obtained by extrapolating HOMO-LUMO gaps and the lowest excitation energies to infinite chain length. The IPs, EAs, and λ abs of the polymers were also obtained by extrapolating those of the oligomers to the inverse chain length equal to zero (1/n ) 0). For PFDBO, IPs and EAs are higher and the band gap is larger than those of PF's from the extrapolation. The outcome shows that the dramatically twisted structure of PFDBO in the seven-membered ring results in the decreased conjugation in the chain. These cause both the maximal absorption and emission wavelengths of PFDBO blue shift compared with PF.
Density functional theory (DFT) is applied to analyze ground-and excited-state properties of the ... more Density functional theory (DFT) is applied to analyze ground-and excited-state properties of the Re(I) halide bipyridine complex ReCl(CO) 3 (bpy) (1) and the related complexes ReCl(CO) 3 (5,5′-dibromo-bpy) (2), ReCl-(CO) 3 (4,4′-dimethyl-bpy) (3), and ReCl(CO) 3 (4,4′-dimethylformyl-bpy) (4) (where bpy ) 2,2′bipyridine). The electronic properties of the neutral molecules, in addition to the positive and negative ions, are studied using the B3LYP functional. Excited singlet and triplet states are examined using time-dependent DFT (TDDFT). The low-lying excited-state geometries are optimized at the ab initio configuration interaction singlets (CIS) level. As shown, the occupied orbitals involved in the transitions have a significant mixture of the metal Re and the group Cl, by the amount of metal 5d character which varies from 30 to 65%. The lowest unoccupied molecular orbital (LUMO) is a π* orbital of the ligand bpy for the series of molecules. The TDDFT result indicates that the absorption maxima are at relatively high energy and are mainly assigned to bpy-based ππ* transitions with somewhat metal-to-ligand charge transfer (MLCT) [d(Re) f π*(bpy)] and ligand-to-ligand charge transfer (LLCT) [p(Cl) f π*(bpy)] except for complex 3, in which this band is mainly assigned to mixed MLCT/LLCT, and overlaps bpy ππ* character. All the low-lying transitions are categorized as mixed MLCT/LLCT. The absorption bands are blue shifted when substituted by an electron-releasing group (-CH 3 ), and they are red shifted when substituted by an electron-withdrawing group (-Br or -COOCH 3 ). The luminescence of all complexes is assigned as a triplet metal/chlorine to bpy charge transfer (MLCT/LLCT).
A theoretical investigation on the electronic and optical properties of p-conjugated copolymers w... more A theoretical investigation on the electronic and optical properties of p-conjugated copolymers with an efficient electron-accepting unit bithieno[3,2-b:2 0 3 0 -e]pyridine [Polymer 46 (2005) 9955-9964]
Density functional theory (DFT) is applied to analyze ground-and excited-state properties of the ... more Density functional theory (DFT) is applied to analyze ground-and excited-state properties of the Re(I) halide bipyridine complex ReCl(CO) 3 (bpy) (1) and the related complexes ReCl(CO) 3 (5,5′-dibromo-bpy) (2), ReCl-(CO) 3 (4,4′-dimethyl-bpy) (3), and ReCl(CO) 3 (4,4′-dimethylformyl-bpy) (4) (where bpy ) 2,2′bipyridine). The electronic properties of the neutral molecules, in addition to the positive and negative ions, are studied using the B3LYP functional. Excited singlet and triplet states are examined using time-dependent DFT (TDDFT). The low-lying excited-state geometries are optimized at the ab initio configuration interaction singlets (CIS) level. As shown, the occupied orbitals involved in the transitions have a significant mixture of the metal Re and the group Cl, by the amount of metal 5d character which varies from 30 to 65%. The lowest unoccupied molecular orbital (LUMO) is a π* orbital of the ligand bpy for the series of molecules. The TDDFT result indicates that the absorption maxima are at relatively high energy and are mainly assigned to bpy-based ππ* transitions with somewhat metal-to-ligand charge transfer (MLCT) [d(Re) f π*(bpy)] and ligand-to-ligand charge transfer (LLCT) [p(Cl) f π*(bpy)] except for complex 3, in which this band is mainly assigned to mixed MLCT/LLCT, and overlaps bpy ππ* character. All the low-lying transitions are categorized as mixed MLCT/LLCT. The absorption bands are blue shifted when substituted by an electron-releasing group (-CH 3 ), and they are red shifted when substituted by an electron-withdrawing group (-Br or -COOCH 3 ). The luminescence of all complexes is assigned as a triplet metal/chlorine to bpy charge transfer (MLCT/LLCT).
First-principles calculations have been performed to determine the effects of Sr doping on the st... more First-principles calculations have been performed to determine the effects of Sr doping on the structural, electronic, and optical properties of ZnONT. The dielectric tensor is derived within the random phase approximation (RPA), and optical properties are calculated for both parallel and perpendicular electric field polarizations to the nanotube axis. It is found that all doped systems are exothermic and stable, but by increasing Sr-doping concentration the formation energy increased. The semiconducting energy gap of Sr-doped single walled ZnONT is bigger than their pristine ZnONT. From the optical property calculations, strong absorptions have been found in the visible-light region for both pristine ZnONT and Sr-doped ZnONT. By increasing concentration of Sr-doped the main absorption edge has a further blue shift to that of pure ZnONT.
Canadian Journal of Chemistry-revue Canadienne De Chimie, 2004
The one-photon absorption (OPA) properties of tetrabenzoporphyrins (TBPs) and phthalocyanines (Pc... more The one-photon absorption (OPA) properties of tetrabenzoporphyrins (TBPs) and phthalocyanines (Pcs) were studied using the semiempirical ZINDO method and time-dependent density functional theory (TDDFT), respectively. The compared results confirmed that the semiempirical ZINDO method was reasonably reliable when calculating the OPA of tetrabenzoporphyrins and phthalocyanines. On the basis of the OPA properties obtained from the ZINDO method, two-photon absorption (TPA) properties of two series of molecules were investigated, using ZINDO and sum-over-states (SOS) methods. The results showed that the TPA cross-sections of all molecules were in the range of 220.6 × 10 -50 -345.9 × 10 -50 cm 4 ·s·photon -1 , which were in the same order of magnitude as the values reported in the literature. The relatively larger δ(ω) value for Pcs with respect to that for corresponding TBPs originates from larger intramolecular charge transfer, which can be characterized by the difference of dipole moment between S 0 and S 1 and the transition dipole moment between S 1 and S 5 .
We have theoretically investigated a series of multiply N-confused porphyrins and their Zn or Cu ... more We have theoretically investigated a series of multiply N-confused porphyrins and their Zn or Cu complexes for the first time by using DFT(B3LYP/6-31G*) and ZINDO/SOS methods. The electronic structure, onephoton absorption (OPA), and two-photon absorption (TPA) properties have been studied in detail. The calculated results indicate that the OPA spectra of multiply N-confused porphyrins are red-shifted and the OPA intensities decrease compared to normal porphyrin. The maximum two photon absorption wavelengths λ max are blue-shifted and the TPA cross sections δ max are increased 22.7-112.1 GM when the N atoms one by one are inverted from core to position to form multiply N-confused porphyrins. Especially δ max of N 3 CP get to 164.7 GM. The electron donors -C 6 F 5 s at meso-position can make the TPA cross section δ max increase. After forming metal complexes with Cu or Zn, the TPA properties of multiply N-confused porphyrins are further increased except for N 3 CP, N 4 CP. Our theoretical findings demonstrate that the multiply N-confused prophyrins as well as their metal complexes and derivatives are promising molecules that can be assembled series of materials with large TPA cross section, and are sure to be the subject of further investigation.
One serious problem associated with polyfluorene derivatives for light-emitting diodes is that th... more One serious problem associated with polyfluorene derivatives for light-emitting diodes is that they are usually much better at accepting and transporting holes than electrons. One way to achieve high electron affinity is the traditional structural modifications by the introduction of electron-withdrawing groups into p-conjugated systems. In this contribution, we apply density functional theory and the timedependent density functional theory to investigate two series of alternating fluorene/pyridine oligomers and copolymers, namely, poly(2,7-(9,9-dimethylfluorene)-alt-3,5-pyridine) (PFPy) and poly(2,7-(9,9-dimethylfluorene-3,5-pyridine-)-alt-2,7-(9,9-dimethylfluorene)) (PFPyF) and gain a detailed understanding of the influence of pyridine units on the electronic and optical properties of fluorene derivatives. The outcomes show the incorporation of pyridine into the polyfluorene (PF) backbone resulted in a broadened energy gap and a blue shift of the absorption peaks. Most importantly, the LUMO energies of PFPy and PFPyF lower about 0.3 eV than that of their corresponding polyfluorene (PF), which directly results in the increasing of EAs than PF, indicating that the pyridine units have significantly improved the electron-accepting properties of the copolymers. In addition, the energy gap tends to broadening and the absorption peaks are gradually blue-shifted to shorter wavelengths with an increase in the pyridine content in the copolymers.
We report on a quantum-chemical study of the electronic and optical properties of gold(I) complex... more We report on a quantum-chemical study of the electronic and optical properties of gold(I) complex AuTFT (1) and its electron-withdrawing substitutents, AuTFOT (2) and AuTFCNT (3) [where TFT = diethynylfluorenyl, TFOT = diethynylfluorenone and TFCNT = diethynyl-(9-(dicyanomethylene)fluorene)]. Our theoretical calculations indicate that for all systems the reorganization energies of electron and hole are in the same order of magnitude and similar to those of the well-known electrontransport material Alq3. The substitution of -CO and -C(CN)2 for -CH in AuTFT significantly decreases the bond length alternation and increases the electron affinity, which would effectively lower the energy barrier for electron injection from cathode and thus qualify AuTFOT (2) and AuTFCNT (3) as candidates for the electron transport layer (ETL) in light-emitting diodes (LEDs). The lowest lying excited-states of gold(I) diethynylfluorenyl derivatives have been studied by the singles configuration interaction (CIS) method and time-dependent density functional method (TDDFT). It is found that the electron-withdrawing substitutions evidently decrease the energy gap, leading to a remarkable red shift in transition energy and transformation in the direction of charge transfer. Our research is important in the development of new functional materials for the design of LEDs with enhanced performance.
One serious problem associated with polyfluorene and derivatives (PFs) as blue luminescent polyme... more One serious problem associated with polyfluorene and derivatives (PFs) as blue luminescent polymers is the significant energy barrier for hole or electron injections; thus they usually face charge injection and transport difficulties with the currently available cathode and anode materials. The incorporation of an electron-donating or -accepting unit is expected to improve the recombination of the charge carriers. In this paper, we apply quantum-chemical techniques to investigate three fluorene-based copolymers, copoly(2,5-ethylenedioxythiophene-alt-9,9'-dimethylfluorene) (PEF), copoly(2,5-pyridine-alt-9,9'-dimethylfluorene) (PPyF), and poly[(fluorene-2,7-diyl)-alt-(1,3,4-oxadiazole-2,5-diyl)] (PFO), in which Delta(H)(-)(L) [the energy difference between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), when n = infinity], the lowest excitation energies (E(g)), ionization potentials (IP), electron affinities (EA), and lambda(abs) and lambda(em) are fine-tuned by the regular insertion of electron-donating unit 3,4-ethylenedioxythiophene (EDOT) or electron-withdrawing units pyridine and 1,3,4-oxadiazole. The results show that the alternate incorporation of electron-donating moiety EDOT increases the HOMO energy and thus reduces the IPs, and consequently the hole injection was greatly improved. On the other hand, even though both kinds of charge carriers will improve the electron-accepting ability, the results show that electron-withdrawing moieties greatly facilitate the electron-transporting. Especially in PFO, the highly planar structural character resulted from the strong push-pull effect between the fluorene ring and the 1,3,4-oxadiazole ring and a weak interaction between the nitrogen and oxygen atoms in 1,3,4-oxadiazole ring and the hydrogen atom of the fluorene ring, significantly lowering the LUMO energy levels and thus improve the electron-accepting and transporting properties by the low LUMO energy levels.
A comparative study of electronic structure, one-photon absorption and two-photon absorption (TPA... more A comparative study of electronic structure, one-photon absorption and two-photon absorption (TPA) properties of octupolar oligofluorenes and their dipolar counterparts is presented by using AM1 and ZINDO-SOS methods. The investigation of the structure-property relationship of these materials has indicated differences between octupolar oligofluorenes and dipolar ones. The results indicate that the conjugated chain length importantly affects the magnitude of TPA cross-section. The dipolar molecules reach a saturation limit for energy gap between HOMO and LUMO versus the number of fluorene rings more quickly than octupolar systems. The maximum TPA cross-section increases in proportion to N a (a = 3.16 and 2.77), where N = 2-6 is the number of fluorene moieties in dipolar molecules and each arm of octupolar analogs. Because of the weak coupling among the branches of the octupole, an increase by a factor of less than 3 of the TPA cross-section of the octupolar molecule with respect to the dipolar molecule occurs.
The geometric and electronic structures of porphyrin and a series of carbaporphyrins have been th... more The geometric and electronic structures of porphyrin and a series of carbaporphyrins have been theoretically studied using the time-dependent density functional theory (TDDFT). The two-photon absorption cross sections (TPACS) of these molecules are computed using the ZINDO-SOS formula. The calculated results indicate that when the N atom is substituted by the C atom, the molecular center is enlarged and the absorptions are red-shifted and that porphyrin, carbaporphyrin, opp-dicarbaporphyrin and adj-dicarbaporphyrin show TPACS in small absorption area, while tetracarbaporphyrin has fairly large two-photon absorptions in comparatively larger area, which may lead it to many practical applications.
We have theoretically investigated a series of butadiyne-linked porphyrin derivatives that exhibi... more We have theoretically investigated a series of butadiyne-linked porphyrin derivatives that exhibit large two-photon absorption (TPA) cross sections in the visible-IR range. The electronic structure, one-photon absorption (OPA), and TPA properties have been studied in detail. We found that the introduction of a butadiyne linkage and the increase of the molecular dimensionality from monomer to dimer determine the OPA intensities of Q band and Soret band, respectively. A most important role for the enhancement of the TPA cross section is played by introducing a butadiyne bridge. The complementary coordination and the combination of the terminal free base and the core zinc porphyrin are also two effective factors for the enhancement of the TPA efficiency. The dimer with two porphyrins linked at meso-positions by a butadiyne linkage results in a maximum TPA cross section (79.35×10−48 cm4 s per photon). Our theoretical findings are consistent with the recent experimental observations. This series of porphyrin derivatives as promising TPA materials are the subject of further investigation.
The molecular equilibrium structures, electronic structures, and one-and two-photon absorption (T... more The molecular equilibrium structures, electronic structures, and one-and two-photon absorption (TPA) properties of C 2V (Zn(II), Fe(II) and Cu(I)) dipolar and D 2d (Zn(II) and Cu(I)) and D 3 (Zn(II)) octupolar metal complexes featuring different functionalized bipyridyl ligands have been studied by the ZINDO-SOS method. The calculated results show that one-and two-photon absorption properties of metal complexes are strongly influenced by the nature of the ligands (donor end groups and π linkers) and metal ions as well as by the symmetry of the complexes. The length of the π-conjugated backbone, the Lewis acidity of the metal ions, and the increase of ligand-to-metal ratio result in a substantial enhancement of the TPA cross sections of metal complexes. Substitution of CdN and NdN for CdC plays an important role in altering the maximum TPA wavelengths and the maximum TPA cross sections of metal complexes. Of them, the CdN substituted metal complexes have relatively large TPA cross sections. Replacing styryl with thienylvinyl makes the onephoton absorption wavelength red shift and at the same time leads to a great decrease of the maximum TPA cross sections of metal complexes. The possible reason is discussed. In the range 500-1250 nm, octupolar metal complexes exhibit intense TPAs and therefore are promising candidates for TPA materials.
Poly(fluorene)-type materials are widely used in polymer-based emitting devices. During operation... more Poly(fluorene)-type materials are widely used in polymer-based emitting devices. During operation there appears, however, an additional emission peak at around 2.3 eV, leading to both a color instability and reduced efficiency. The incorporation of the carbazole units has been proven to efficiently suppress the keto defect emission. In this contribution, we apply quantum-chemical techniques to investigate two series of alternating fluorene/carbazole oligomers and copolymers poly[2,7-(N-(2-methyl)-carbazole)-co-alt-2,7-m(9,9-dimethylfluorene)], namely, PFmCz (m ϭ 1,2) and gain a detailed understanding of the influence of carbazole units on the electronic and optical properties of fluorene derivatives. The electronic properties of the neutral molecules, HOMO-LUMO gaps (⌬ H-L ), in addition to the positive and negative ions, are studied using B3LYP functional. The lowest excitation energies (E g s) and the maximal absorption wavelength abs of PFmCz (m ϭ 1,2) are studied, employing the time-dependent density functional theory (TD-DFT). The properties of the two copolymers, such as ⌬ H-L , E g , IPs, and EAs were obtained by extrapolating those of the oligomers to the inverse chain length equal to zero (1/n ϭ 0). The outcomes showed that the carbazole unit is a good electron-donating moiety for electronic materials, and the incorporation of carbazole into the polyfluorene (PF) backbone resulted in a broadened energy gap and a blue shift of both the absorption and photoluminescence emission peaks. Most importantly, the HOMO energies of PF1Cz and PF2Cz are both a higher average (0.4 eV) than polyfluorene (PF), which directly results in the decreasing of IPs of about 0.2 eV more than PF, indicating that the carbazole units have significantly improved the hole injection properties of the copolymers. In addition, the energy gap tends to broaden and the absorption and emission peaks are gradually blue-shifted to shorter wavelengths with an increase in the carbazole content in the copolymers. This is due to the interruption of the longer conjugation length of the backbone in the (F1Cz) n series.
Poly(fluorene)-type materials are widely used in polymer-based emitting devices. One of the drawb... more Poly(fluorene)-type materials are widely used in polymer-based emitting devices. One of the drawbacks of light-emitting diodes based on polyfluorene derivatives is the injection of holes from the anode due to the high ionization potential (IP) of most derivatives. Substitution by electrondonating alkoxy substituents or by adding charge carriers on the conjugated polymer's backbone produces a remarkable influence on its electrical and optical properties. In this contribution, we apply quantum-chemical techniques to investigate a family of π-conjugated polymers with substituted dimethoxy groups at the 3,6 positions of the fluorene ring, namely, poly(2,7-(3,6dimethoxy-fluorene)(PDMOF), poly(2,7-(3,6-dimethoxy-fluorene)-co-alt-fluorene (PDMOFF), and poly(2,7-(3,6-dimeth-oxy-fluorene)-co-alt-2,5-thiophene (PDMOFT). The electronic properties of the neutral molecules, HOMO-LUMO gaps (∆ H-L ), in addition to the positive and negative ions, are studied using the B3LYP functional. The lowest excitation energies (E g ) and the maximal absorption wavelength λ abs of PDMOF, PDMOFF, and PDMOFT are studied by employing time-dependent density functional theory (TD-DFT) and the ZINDO semiempirical method. The IP, EA, and E g values of each polymer were obtained by extrapolating those of the oligomers to the inverse chain length equal to zero ( 1 / n ) 0). The influence of the presence of methoxy groups on the fluorene moiety on the ionization potential is especially emphasized. The outcomes show that the HOMO energies of these systems under study increase by about 0.4 eV and the IP values decrease by about 0.3 eV compared to those of the corresponding polyfluorene. Both effects result in a reduction of the energy barrier for the injection of holes in related polymeric light-emitting devices and should contribute to the enhancement of their performances. Because of the cooperation with thiophene in PDMOFT, which results in a good planar conformation, both the hole-creating and electronaccepting abilities are improved.
To investigate the protective effects of magnolol on sepsis-induced inflammation and intestinal d... more To investigate the protective effects of magnolol on sepsis-induced inflammation and intestinal dysmotility.
The structures, ionization potentials (IPs), electron affinities (EAs), and HOMO-LUMO gaps (∆ H-L... more The structures, ionization potentials (IPs), electron affinities (EAs), and HOMO-LUMO gaps (∆ H-L) of the oligomers are studied by the density functional theory with B3LYP functional. The lowest excitation energies (Egs) and the maximal absorption wavelength λabs of oligomers of polyfluorene (PF) and poly(2,7-fluorene-alt-co-5,7-dihydrodibenz[c,e]oxepin) (PFDBO) are studied employing the timedependent density functional theory (TD-DFT) and ZINDO. Band gaps and effective conjugation lengths of the corresponding polymers were obtained by extrapolating HOMO-LUMO gaps and the lowest excitation energies to infinite chain length. The IPs, EAs, and λ abs of the polymers were also obtained by extrapolating those of the oligomers to the inverse chain length equal to zero (1/n ) 0). For PFDBO, IPs and EAs are higher and the band gap is larger than those of PF's from the extrapolation. The outcome shows that the dramatically twisted structure of PFDBO in the seven-membered ring results in the decreased conjugation in the chain. These cause both the maximal absorption and emission wavelengths of PFDBO blue shift compared with PF.
Density functional theory (DFT) is applied to analyze ground-and excited-state properties of the ... more Density functional theory (DFT) is applied to analyze ground-and excited-state properties of the Re(I) halide bipyridine complex ReCl(CO) 3 (bpy) (1) and the related complexes ReCl(CO) 3 (5,5′-dibromo-bpy) (2), ReCl-(CO) 3 (4,4′-dimethyl-bpy) (3), and ReCl(CO) 3 (4,4′-dimethylformyl-bpy) (4) (where bpy ) 2,2′bipyridine). The electronic properties of the neutral molecules, in addition to the positive and negative ions, are studied using the B3LYP functional. Excited singlet and triplet states are examined using time-dependent DFT (TDDFT). The low-lying excited-state geometries are optimized at the ab initio configuration interaction singlets (CIS) level. As shown, the occupied orbitals involved in the transitions have a significant mixture of the metal Re and the group Cl, by the amount of metal 5d character which varies from 30 to 65%. The lowest unoccupied molecular orbital (LUMO) is a π* orbital of the ligand bpy for the series of molecules. The TDDFT result indicates that the absorption maxima are at relatively high energy and are mainly assigned to bpy-based ππ* transitions with somewhat metal-to-ligand charge transfer (MLCT) [d(Re) f π*(bpy)] and ligand-to-ligand charge transfer (LLCT) [p(Cl) f π*(bpy)] except for complex 3, in which this band is mainly assigned to mixed MLCT/LLCT, and overlaps bpy ππ* character. All the low-lying transitions are categorized as mixed MLCT/LLCT. The absorption bands are blue shifted when substituted by an electron-releasing group (-CH 3 ), and they are red shifted when substituted by an electron-withdrawing group (-Br or -COOCH 3 ). The luminescence of all complexes is assigned as a triplet metal/chlorine to bpy charge transfer (MLCT/LLCT).
A theoretical investigation on the electronic and optical properties of p-conjugated copolymers w... more A theoretical investigation on the electronic and optical properties of p-conjugated copolymers with an efficient electron-accepting unit bithieno[3,2-b:2 0 3 0 -e]pyridine [Polymer 46 (2005) 9955-9964]
Density functional theory (DFT) is applied to analyze ground-and excited-state properties of the ... more Density functional theory (DFT) is applied to analyze ground-and excited-state properties of the Re(I) halide bipyridine complex ReCl(CO) 3 (bpy) (1) and the related complexes ReCl(CO) 3 (5,5′-dibromo-bpy) (2), ReCl-(CO) 3 (4,4′-dimethyl-bpy) (3), and ReCl(CO) 3 (4,4′-dimethylformyl-bpy) (4) (where bpy ) 2,2′bipyridine). The electronic properties of the neutral molecules, in addition to the positive and negative ions, are studied using the B3LYP functional. Excited singlet and triplet states are examined using time-dependent DFT (TDDFT). The low-lying excited-state geometries are optimized at the ab initio configuration interaction singlets (CIS) level. As shown, the occupied orbitals involved in the transitions have a significant mixture of the metal Re and the group Cl, by the amount of metal 5d character which varies from 30 to 65%. The lowest unoccupied molecular orbital (LUMO) is a π* orbital of the ligand bpy for the series of molecules. The TDDFT result indicates that the absorption maxima are at relatively high energy and are mainly assigned to bpy-based ππ* transitions with somewhat metal-to-ligand charge transfer (MLCT) [d(Re) f π*(bpy)] and ligand-to-ligand charge transfer (LLCT) [p(Cl) f π*(bpy)] except for complex 3, in which this band is mainly assigned to mixed MLCT/LLCT, and overlaps bpy ππ* character. All the low-lying transitions are categorized as mixed MLCT/LLCT. The absorption bands are blue shifted when substituted by an electron-releasing group (-CH 3 ), and they are red shifted when substituted by an electron-withdrawing group (-Br or -COOCH 3 ). The luminescence of all complexes is assigned as a triplet metal/chlorine to bpy charge transfer (MLCT/LLCT).
First-principles calculations have been performed to determine the effects of Sr doping on the st... more First-principles calculations have been performed to determine the effects of Sr doping on the structural, electronic, and optical properties of ZnONT. The dielectric tensor is derived within the random phase approximation (RPA), and optical properties are calculated for both parallel and perpendicular electric field polarizations to the nanotube axis. It is found that all doped systems are exothermic and stable, but by increasing Sr-doping concentration the formation energy increased. The semiconducting energy gap of Sr-doped single walled ZnONT is bigger than their pristine ZnONT. From the optical property calculations, strong absorptions have been found in the visible-light region for both pristine ZnONT and Sr-doped ZnONT. By increasing concentration of Sr-doped the main absorption edge has a further blue shift to that of pure ZnONT.
Canadian Journal of Chemistry-revue Canadienne De Chimie, 2004
The one-photon absorption (OPA) properties of tetrabenzoporphyrins (TBPs) and phthalocyanines (Pc... more The one-photon absorption (OPA) properties of tetrabenzoporphyrins (TBPs) and phthalocyanines (Pcs) were studied using the semiempirical ZINDO method and time-dependent density functional theory (TDDFT), respectively. The compared results confirmed that the semiempirical ZINDO method was reasonably reliable when calculating the OPA of tetrabenzoporphyrins and phthalocyanines. On the basis of the OPA properties obtained from the ZINDO method, two-photon absorption (TPA) properties of two series of molecules were investigated, using ZINDO and sum-over-states (SOS) methods. The results showed that the TPA cross-sections of all molecules were in the range of 220.6 × 10 -50 -345.9 × 10 -50 cm 4 ·s·photon -1 , which were in the same order of magnitude as the values reported in the literature. The relatively larger δ(ω) value for Pcs with respect to that for corresponding TBPs originates from larger intramolecular charge transfer, which can be characterized by the difference of dipole moment between S 0 and S 1 and the transition dipole moment between S 1 and S 5 .
We have theoretically investigated a series of multiply N-confused porphyrins and their Zn or Cu ... more We have theoretically investigated a series of multiply N-confused porphyrins and their Zn or Cu complexes for the first time by using DFT(B3LYP/6-31G*) and ZINDO/SOS methods. The electronic structure, onephoton absorption (OPA), and two-photon absorption (TPA) properties have been studied in detail. The calculated results indicate that the OPA spectra of multiply N-confused porphyrins are red-shifted and the OPA intensities decrease compared to normal porphyrin. The maximum two photon absorption wavelengths λ max are blue-shifted and the TPA cross sections δ max are increased 22.7-112.1 GM when the N atoms one by one are inverted from core to position to form multiply N-confused porphyrins. Especially δ max of N 3 CP get to 164.7 GM. The electron donors -C 6 F 5 s at meso-position can make the TPA cross section δ max increase. After forming metal complexes with Cu or Zn, the TPA properties of multiply N-confused porphyrins are further increased except for N 3 CP, N 4 CP. Our theoretical findings demonstrate that the multiply N-confused prophyrins as well as their metal complexes and derivatives are promising molecules that can be assembled series of materials with large TPA cross section, and are sure to be the subject of further investigation.
One serious problem associated with polyfluorene derivatives for light-emitting diodes is that th... more One serious problem associated with polyfluorene derivatives for light-emitting diodes is that they are usually much better at accepting and transporting holes than electrons. One way to achieve high electron affinity is the traditional structural modifications by the introduction of electron-withdrawing groups into p-conjugated systems. In this contribution, we apply density functional theory and the timedependent density functional theory to investigate two series of alternating fluorene/pyridine oligomers and copolymers, namely, poly(2,7-(9,9-dimethylfluorene)-alt-3,5-pyridine) (PFPy) and poly(2,7-(9,9-dimethylfluorene-3,5-pyridine-)-alt-2,7-(9,9-dimethylfluorene)) (PFPyF) and gain a detailed understanding of the influence of pyridine units on the electronic and optical properties of fluorene derivatives. The outcomes show the incorporation of pyridine into the polyfluorene (PF) backbone resulted in a broadened energy gap and a blue shift of the absorption peaks. Most importantly, the LUMO energies of PFPy and PFPyF lower about 0.3 eV than that of their corresponding polyfluorene (PF), which directly results in the increasing of EAs than PF, indicating that the pyridine units have significantly improved the electron-accepting properties of the copolymers. In addition, the energy gap tends to broadening and the absorption peaks are gradually blue-shifted to shorter wavelengths with an increase in the pyridine content in the copolymers.
We report on a quantum-chemical study of the electronic and optical properties of gold(I) complex... more We report on a quantum-chemical study of the electronic and optical properties of gold(I) complex AuTFT (1) and its electron-withdrawing substitutents, AuTFOT (2) and AuTFCNT (3) [where TFT = diethynylfluorenyl, TFOT = diethynylfluorenone and TFCNT = diethynyl-(9-(dicyanomethylene)fluorene)]. Our theoretical calculations indicate that for all systems the reorganization energies of electron and hole are in the same order of magnitude and similar to those of the well-known electrontransport material Alq3. The substitution of -CO and -C(CN)2 for -CH in AuTFT significantly decreases the bond length alternation and increases the electron affinity, which would effectively lower the energy barrier for electron injection from cathode and thus qualify AuTFOT (2) and AuTFCNT (3) as candidates for the electron transport layer (ETL) in light-emitting diodes (LEDs). The lowest lying excited-states of gold(I) diethynylfluorenyl derivatives have been studied by the singles configuration interaction (CIS) method and time-dependent density functional method (TDDFT). It is found that the electron-withdrawing substitutions evidently decrease the energy gap, leading to a remarkable red shift in transition energy and transformation in the direction of charge transfer. Our research is important in the development of new functional materials for the design of LEDs with enhanced performance.
One serious problem associated with polyfluorene and derivatives (PFs) as blue luminescent polyme... more One serious problem associated with polyfluorene and derivatives (PFs) as blue luminescent polymers is the significant energy barrier for hole or electron injections; thus they usually face charge injection and transport difficulties with the currently available cathode and anode materials. The incorporation of an electron-donating or -accepting unit is expected to improve the recombination of the charge carriers. In this paper, we apply quantum-chemical techniques to investigate three fluorene-based copolymers, copoly(2,5-ethylenedioxythiophene-alt-9,9'-dimethylfluorene) (PEF), copoly(2,5-pyridine-alt-9,9'-dimethylfluorene) (PPyF), and poly[(fluorene-2,7-diyl)-alt-(1,3,4-oxadiazole-2,5-diyl)] (PFO), in which Delta(H)(-)(L) [the energy difference between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), when n = infinity], the lowest excitation energies (E(g)), ionization potentials (IP), electron affinities (EA), and lambda(abs) and lambda(em) are fine-tuned by the regular insertion of electron-donating unit 3,4-ethylenedioxythiophene (EDOT) or electron-withdrawing units pyridine and 1,3,4-oxadiazole. The results show that the alternate incorporation of electron-donating moiety EDOT increases the HOMO energy and thus reduces the IPs, and consequently the hole injection was greatly improved. On the other hand, even though both kinds of charge carriers will improve the electron-accepting ability, the results show that electron-withdrawing moieties greatly facilitate the electron-transporting. Especially in PFO, the highly planar structural character resulted from the strong push-pull effect between the fluorene ring and the 1,3,4-oxadiazole ring and a weak interaction between the nitrogen and oxygen atoms in 1,3,4-oxadiazole ring and the hydrogen atom of the fluorene ring, significantly lowering the LUMO energy levels and thus improve the electron-accepting and transporting properties by the low LUMO energy levels.
A comparative study of electronic structure, one-photon absorption and two-photon absorption (TPA... more A comparative study of electronic structure, one-photon absorption and two-photon absorption (TPA) properties of octupolar oligofluorenes and their dipolar counterparts is presented by using AM1 and ZINDO-SOS methods. The investigation of the structure-property relationship of these materials has indicated differences between octupolar oligofluorenes and dipolar ones. The results indicate that the conjugated chain length importantly affects the magnitude of TPA cross-section. The dipolar molecules reach a saturation limit for energy gap between HOMO and LUMO versus the number of fluorene rings more quickly than octupolar systems. The maximum TPA cross-section increases in proportion to N a (a = 3.16 and 2.77), where N = 2-6 is the number of fluorene moieties in dipolar molecules and each arm of octupolar analogs. Because of the weak coupling among the branches of the octupole, an increase by a factor of less than 3 of the TPA cross-section of the octupolar molecule with respect to the dipolar molecule occurs.
The geometric and electronic structures of porphyrin and a series of carbaporphyrins have been th... more The geometric and electronic structures of porphyrin and a series of carbaporphyrins have been theoretically studied using the time-dependent density functional theory (TDDFT). The two-photon absorption cross sections (TPACS) of these molecules are computed using the ZINDO-SOS formula. The calculated results indicate that when the N atom is substituted by the C atom, the molecular center is enlarged and the absorptions are red-shifted and that porphyrin, carbaporphyrin, opp-dicarbaporphyrin and adj-dicarbaporphyrin show TPACS in small absorption area, while tetracarbaporphyrin has fairly large two-photon absorptions in comparatively larger area, which may lead it to many practical applications.
We have theoretically investigated a series of butadiyne-linked porphyrin derivatives that exhibi... more We have theoretically investigated a series of butadiyne-linked porphyrin derivatives that exhibit large two-photon absorption (TPA) cross sections in the visible-IR range. The electronic structure, one-photon absorption (OPA), and TPA properties have been studied in detail. We found that the introduction of a butadiyne linkage and the increase of the molecular dimensionality from monomer to dimer determine the OPA intensities of Q band and Soret band, respectively. A most important role for the enhancement of the TPA cross section is played by introducing a butadiyne bridge. The complementary coordination and the combination of the terminal free base and the core zinc porphyrin are also two effective factors for the enhancement of the TPA efficiency. The dimer with two porphyrins linked at meso-positions by a butadiyne linkage results in a maximum TPA cross section (79.35×10−48 cm4 s per photon). Our theoretical findings are consistent with the recent experimental observations. This series of porphyrin derivatives as promising TPA materials are the subject of further investigation.
The molecular equilibrium structures, electronic structures, and one-and two-photon absorption (T... more The molecular equilibrium structures, electronic structures, and one-and two-photon absorption (TPA) properties of C 2V (Zn(II), Fe(II) and Cu(I)) dipolar and D 2d (Zn(II) and Cu(I)) and D 3 (Zn(II)) octupolar metal complexes featuring different functionalized bipyridyl ligands have been studied by the ZINDO-SOS method. The calculated results show that one-and two-photon absorption properties of metal complexes are strongly influenced by the nature of the ligands (donor end groups and π linkers) and metal ions as well as by the symmetry of the complexes. The length of the π-conjugated backbone, the Lewis acidity of the metal ions, and the increase of ligand-to-metal ratio result in a substantial enhancement of the TPA cross sections of metal complexes. Substitution of CdN and NdN for CdC plays an important role in altering the maximum TPA wavelengths and the maximum TPA cross sections of metal complexes. Of them, the CdN substituted metal complexes have relatively large TPA cross sections. Replacing styryl with thienylvinyl makes the onephoton absorption wavelength red shift and at the same time leads to a great decrease of the maximum TPA cross sections of metal complexes. The possible reason is discussed. In the range 500-1250 nm, octupolar metal complexes exhibit intense TPAs and therefore are promising candidates for TPA materials.
Poly(fluorene)-type materials are widely used in polymer-based emitting devices. During operation... more Poly(fluorene)-type materials are widely used in polymer-based emitting devices. During operation there appears, however, an additional emission peak at around 2.3 eV, leading to both a color instability and reduced efficiency. The incorporation of the carbazole units has been proven to efficiently suppress the keto defect emission. In this contribution, we apply quantum-chemical techniques to investigate two series of alternating fluorene/carbazole oligomers and copolymers poly[2,7-(N-(2-methyl)-carbazole)-co-alt-2,7-m(9,9-dimethylfluorene)], namely, PFmCz (m ϭ 1,2) and gain a detailed understanding of the influence of carbazole units on the electronic and optical properties of fluorene derivatives. The electronic properties of the neutral molecules, HOMO-LUMO gaps (⌬ H-L ), in addition to the positive and negative ions, are studied using B3LYP functional. The lowest excitation energies (E g s) and the maximal absorption wavelength abs of PFmCz (m ϭ 1,2) are studied, employing the time-dependent density functional theory (TD-DFT). The properties of the two copolymers, such as ⌬ H-L , E g , IPs, and EAs were obtained by extrapolating those of the oligomers to the inverse chain length equal to zero (1/n ϭ 0). The outcomes showed that the carbazole unit is a good electron-donating moiety for electronic materials, and the incorporation of carbazole into the polyfluorene (PF) backbone resulted in a broadened energy gap and a blue shift of both the absorption and photoluminescence emission peaks. Most importantly, the HOMO energies of PF1Cz and PF2Cz are both a higher average (0.4 eV) than polyfluorene (PF), which directly results in the decreasing of IPs of about 0.2 eV more than PF, indicating that the carbazole units have significantly improved the hole injection properties of the copolymers. In addition, the energy gap tends to broaden and the absorption and emission peaks are gradually blue-shifted to shorter wavelengths with an increase in the carbazole content in the copolymers. This is due to the interruption of the longer conjugation length of the backbone in the (F1Cz) n series.
Poly(fluorene)-type materials are widely used in polymer-based emitting devices. One of the drawb... more Poly(fluorene)-type materials are widely used in polymer-based emitting devices. One of the drawbacks of light-emitting diodes based on polyfluorene derivatives is the injection of holes from the anode due to the high ionization potential (IP) of most derivatives. Substitution by electrondonating alkoxy substituents or by adding charge carriers on the conjugated polymer's backbone produces a remarkable influence on its electrical and optical properties. In this contribution, we apply quantum-chemical techniques to investigate a family of π-conjugated polymers with substituted dimethoxy groups at the 3,6 positions of the fluorene ring, namely, poly(2,7-(3,6dimethoxy-fluorene)(PDMOF), poly(2,7-(3,6-dimethoxy-fluorene)-co-alt-fluorene (PDMOFF), and poly(2,7-(3,6-dimeth-oxy-fluorene)-co-alt-2,5-thiophene (PDMOFT). The electronic properties of the neutral molecules, HOMO-LUMO gaps (∆ H-L ), in addition to the positive and negative ions, are studied using the B3LYP functional. The lowest excitation energies (E g ) and the maximal absorption wavelength λ abs of PDMOF, PDMOFF, and PDMOFT are studied by employing time-dependent density functional theory (TD-DFT) and the ZINDO semiempirical method. The IP, EA, and E g values of each polymer were obtained by extrapolating those of the oligomers to the inverse chain length equal to zero ( 1 / n ) 0). The influence of the presence of methoxy groups on the fluorene moiety on the ionization potential is especially emphasized. The outcomes show that the HOMO energies of these systems under study increase by about 0.4 eV and the IP values decrease by about 0.3 eV compared to those of the corresponding polyfluorene. Both effects result in a reduction of the energy barrier for the injection of holes in related polymeric light-emitting devices and should contribute to the enhancement of their performances. Because of the cooperation with thiophene in PDMOFT, which results in a good planar conformation, both the hole-creating and electronaccepting abilities are improved.
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Papers by Ai Ren