With density functional theory(DFT) method, the optimization of molecular configurations and the calculation of frontier molecular orbitals were achieved for triphenylamine(TPA)-based dye-sensitized solar cell materials at the B3LYP/6-31G(d, p) level. Time-dependent density functional theory(TD-DFT) was applied to calculating the probability of the transition from the ground state to the excited state. And UV-Vis absorption spectra were derived with Franck-Condon approximation. The conjugation length, substitution groups and spatial effects show a slight influence on the dihedral angle of the TPA group. The increase of conjugation length may cause a smaller energy gap as well as a higher highest occupied molecular orbital(HOMO) and a lower lowest unoccupied molecular orbital (LUMO). The introduction of methoxyl group and TPA group could lower the energy gap while the HOMO and LUMO were elevated in energy. 相似文献
Undecacene, the largest member of the acene family, was photogenerated in a polymer matrix under cryogenic conditions from a precursor with two α‐diketone bridges. The electronic absorption of undecacene extends into the NIR region, but the spectrum is dominated by two strong absorptions in the UV/Vis range. The HOMO–LUMO transition is continuously shifted to lower energies as the number of rings of the acene increases (E vs. 1/N, N=number of rings), which is in line with the strong electron correlation calculated by DFT/MRCI. 相似文献
Phthalocyanine (Pc) molecules are well‐known flexible structural units for 1D nanotubes and 2D nanosheets. First‐principles calculations combined with grand canonical Monte Carlo simulations are used to obtain the geometries, electronic structures, optical properties, and hydrogen‐storage capacities of nanocages consisting of six Pc molecules with six Mg or Ca atoms. The primitive Pc cage has Th symmetry with twofold degeneracy in the highest occupied molecular orbital (HOMO), and threefold degeneracy in the lowest unoccupied molecular orbital (LUMO); the corresponding HOMO–LUMO gap is found to be 0.97 eV. The MgPc and CaPc cages have Oh symmetry with a HOMO–LUMO gap of 1.24 and 1.13 eV, respectively. Optical absorption spectra suggest that the Pc‐based cages can absorb infrared light, which is different from the visible‐light absorption in Pc molecules. We further show that the excess uptake of hydrogen on MgPc and CaPc cages at 298 K and 100 bar (1 bar=0.1 MPa) is about 3.49 and 4.74 wt %, respectively. The present study provides new insight into Pc‐based nanostructures with potential applications. 相似文献
Density-functional theory studies were applied to investigate the structural, electronic, and optical properties of 9-heterofluorenes achieved by substituting the carbon at 9 position of fluorene with silicon, germanium, nitrogen, phosphor, oxygen, sulfur, selenium, or boron. These heterofluorenes and their oligomers up to pentamers are highly aromatic and electrooptically active. The alkyl and aryl substituents of the heteroatom have limited influence, but the oxidation of the atom has significant influence on their molecular structures and properties. The highest occupied molecular orbital (HOMO)-lowest occupied molecular orbital (LUMO) interaction theory was successfully applied to analyze the energy levels and the frontier wave functions of these heterofluorenes. Most heterofluorenes belong to type B of interaction with low-lying LUMO and have the second kind of wave function. Carbazole and selenafluorene have type C of interaction with high-lying HOMO and the third kind of wave function. Types C and D of heterofluorenes, such as carbazole, oxygafluorene, sulfurafluorene, and selenafluorene also have high triplet state energies. The extrapolated HOMO and LUMO for polyheterofluorenes indicate that polyselenonafluorene has the lowest LUMO; polycarbazole has the highest HOMO; polyselenafluorene has the highest bandgap (E(g)); and polyborafluorene has the lowest E(g). Heterofluorenes and their oligomers and polymers are of great experimental interests, especially those having extraordinary properties revealed in this study. 相似文献
Both C‐H bonding and antibonding (σCH and σ*CH) of a methyl group would contribute to the highest occupied or lowest unoccupied molecular orbitals (HOMO or LUMO) in methylated derivatives of Ir(ppz)2 3 iq (ppz = 1‐phenylpyrazole and 3iq = isoquinoline‐3‐carboxylate). This is found by analysis of HOMO (or LUMO) formed by linear combination of bond orbitals using the natural bond orbital (NBO) method. The elevated level of HOMO (or LUMO) uniformly found for each methylated derivative, indicating the σCH‐destabilization outweighs the σ*CH‐stabilization. To broaden the HOMO‐LUMO gap, methylation at a carbon having smaller contribution to HOMO and/or larger contribution to LUMO is suggested. 相似文献
Tetrameric porphyrin formation of 2‐hydroxymethylpyrrole fused with porphyrins through a bicyclo[2.2.2]octadiene unit gave bicyclo[2.2.2]octadiene‐fused porphyrin pentamers. Thermal conversion of the pentamers gave fully π‐conjugated cruciform porphyrin pentamers fused with benzene units in quantitative yields. UV/Vis spectra of fully π‐conjugated porphyrin pentamers showed one very strong Q absorption and were quite different from those of usual porphyrins. From TD‐DFT calculations, the HOMO level is 0.49 eV higher than the HOMO?1 level. The LUMO and LUMO+1 levels are very close and are lower by more than 0.27 eV than those of other unoccupied MOs. The strong Q absorption was interpreted as two mutually orthogonal single‐electron transitions (683 nm: 86 %, HOMO→LUMO; 680 nm: 86 %, HOMO→LUMO+1). The two‐photon absorption (TPA) cross section value (σ(2)) of the benzene‐fused porphyrin pentamer was estimated to be 3900 GM at 1500 nm, which is strongly correlated with a cruciform molecular structure with multidirectional π‐conjugation pathways. 相似文献
Homodisperse doped polyoxotitanate nanoclusters with formulae Ti11(MX)O14(OiPr)17 (M=Mn, Fe or Co; X=Cl, Br or I, OiPr=isopropoxide) display strongly dopant‐dependent properties. Spectroscopic solution and reflectance measurements backed up by density of states and time‐dependent DFT calculations based on the determined structures, show the prominent effect of FeX substitution by decreasing the HOMO–LUMO gap of the particles. The effect is attributed to the presence of an occupied Fe β orbital halfway up the bandgap, leading to long‐wavelength absorption with electron transfer to the titanium atoms of the cluster. Whereas the light absorption varies significantly with variation of the transition metal dopant, its dependency on the nature of the halogen atom or the change in dipole moment across the series is minor. 相似文献
The relationships between electronic structures and spectra properties are investigated by DFT/TDDFT for terthiophene derivatives, BMA‐3T (tri‐aryl amine end‐capped terthiophene), BBA‐3T (tri‐aryl amine and tri‐aryl boron end‐capped terthiophene) and BPB‐3T (tri‐aryl boron end‐capped terthiophene). The calculated results show that BMA‐3T, BBA‐3T and BPB‐3T have higher HOMO energy level and lower ionization potentials (IPs) than 3T. BMA‐3T has good hole injection ability and hole‐transport property as reported in experiment. The designed molecule of BBA‐3T and BPB‐3T own lower LUMO level and higher electron affinities (EAs) than BMA‐3T, which facilitate electron injection and improve their electron‐transport properties. Surprisingly, BPB‐3T has preferable charge equilibrium property since its hole reorganization energy (λh) is close to electron reorganization energy (λe). The ΔE (HOMO−LUMO) and Eg of these three derivatives are narrower compared to 3T, and the absorption as well as emission spectrum exhibited red‐shifts. 相似文献
Two new low‐bandgap block copolymers derived from dithienylbenzothiadiazole (DTBT) and different electron‐rich functional groups (dioctoxyl benzene and N‐octyl‐diphenylamine), poly(1,4‐dioctoxyl‐2,5‐divinylbenzene‐co‐4,7‐dithiophene‐2′‐yl‐2,1,3‐benzothiadiazole) (PPV‐DTBT), poly(3,8‐divinyl‐N‐octyl‐diphenylamine‐co‐4,7‐dithiophene‐2′‐yl‐2,1,3‐benzothiadiazole) (PDPAV‐DTBT), were synthesized by Heck cross‐coupling polymerization. PPV‐DTBT and PDPAV‐DTBT are easily soluble in common organic solvents such as o‐dichlorobenzene and chloroform. DSC and TGA results indicate that these copolymers possess good thermal stabilities. PPV‐DTBT and PDPAV‐DTBT films exhibit broad absorption bands at 300–765 nm (with an optical bandgap of 1.62 eV) and 300–733 nm (with an optical bandgap of 1.69 eV), respectively. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of PPV‐DTBT were estimated by cyclic voltammetry to be −5.43 and −3.74 eV, respectively, and the HOMO and LUMO of PDPAV‐DTBT were −5.37 and −3.7 eV, respectively. Preliminary photovoltaic cells based on the composite structure of ITO/PEDOT: PSS/PPV‐DTBT:PCBM (1: 2, w/w)/Al showed an open‐circuit voltage of 0.75 V, a power conversion efficiency of 0.6%, and a short circuit current of 1.7 mA · cm−2.
A semiempirical PM3 quantum computational method has been used to generate the electronic and optimized geometrical structure of SWNT of zigzag and armchair types. We shed light on the electronic structures of SWNT with various diameters and lengths of the tube. Particularly, the calculated HOMO, LUMO and band‐gap of SWNT are not monotonic but exhibit a well‐defined oscillation, which depends on the tubular diameter and the tubular length. Calculated HOMO, LUMO and band‐gap of the zigzag SWNTs have oscillated with tubular diameter as they contain an odd or even number of benzenoids in the circular plane of the carbon nanotube. The zigzag SWNTs with an odd number of benzenoids have a higher band‐gap than those of SWNTs with an even number of benzenoids in the circular plane of the carbon nanotube. Calculated results also reveal that the tubular length in the zigzag SWNTs influences the band‐gaps very little. For the armchair SWNT, calculated HOMO, LUMO and band‐gap contained the oscillate depending on the number of carbon sections in the tubular length axis. Their repeat sections are 3n‐1, 3n and 3n+1. The armchair SWNT with 3n+1 sections has a high band‐gap while the SWNTs with 3n‐1 sections have a low band‐gap. The tubular diameters of armchair SWNT influence the HOMO, LUMO and band gap very little. 相似文献
Electron‐donating molecules play an important role in the development of organic solar cells. (Z )‐2‐(2‐Phenylhydrazinylidene)acenaphthen‐1(2H )‐one (PDAK), C18H12N2O, was synthesized by a Schiff base reaction. The crystal structure shows that the molecules are planar and are linked together forming `face‐to‐face' assemblies held together by intermolecular C—H…O, π–π and C—H…π interactions. PDAK exhibits a broadband UV–Vis absorption (200–648 nm) and a low HOMO–LUMO energy gap (1.91 eV; HOMO is the highest occupied molecular orbital and LUMO is the lowest unoccupied molecular orbital), while fluorescence quenching experiments provide evidence for electron transfer from the excited state of PDAK to C60. This suggests that the title molecule may be a suitable donor for use in organic solar cells. 相似文献
New thieno[3,4-b]thiophene derivatives were prepared via a short and versatile synthetic route. Electrochemical studies of 2-heptenylthieno[3,4-b]thiophene, 2-styrylthieno[3,4-b]thiophene, and 2-phenyl-3-(thieno[3,4-b]thiophene-2-yl)acrylonitrile and the corresponding polymers revealed that raising the HOMO and lowering the LUMO can be attained by functionalizing thieno[3,4-b]thiophene with aromatic resonance-enhancing and electron-withdrawing groups. The bandgap of resulting polymers varied from 0.78 to 1.0 eV, indicating that poly(2-phenyl-3-(thieno[3,4-b]thiophene-2-yl)acrylonitrile) is one of the lowest bandgap polymers ever reported. 相似文献
Herein, we study the π‐conjugational properties of a homologous series of all‐anti oligothienoacenes containing four to eight fused thiophene rings by means of FT Raman spectroscopy and DFT calculations. The theoretical analysis of the spectroscopic data provides evidence that selective enhancement of a very limited number of Raman scatterings is related to the occurrence in these oligothienoacenes of strong vibronic coupling between collective ν(C?C) stretching modes in the 1600–1300 cm?1 region and the HOMO/LUMO frontier orbitals (HOMO=highest occupied molecular orbital; LUMO=lowest unoccupied molecular orbital). The correlation of the Raman spectroscopic data and theoretical results for these all‐anti oligothienoacenes with those previously collected for a number of all‐syn oligothienohelicenes gives further support to the expectation that cross‐conjugation is dominant in heterohelicenes. Fully planar all‐anti oligothienoacenes display linear π conjugation which seemingly does not reach saturation with increasing number of annulated thiophene rings in the oligomeric chain at least up to the octamer.相似文献