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Two important classes of organic molecules, perylene diimide (PDI) and pyrene derivatives have been found to possess relatively excellent photophysical and photochemical properties and especially high two-photon absorption cross sections ( δ). Herein, one-photon absorption (OPA) and two-photon absorption (TPA) properties of some novel PDI and pyrene derivatives were comparatively investigated by the density functional theory (DFT) and Zerner's intermediate neglect of differential overlap (ZINDO) methods. The calculated results indicate that with respect to PDI derivatives, the maximum TPA cross-sections for pyrene compounds increase obviously, the maximum peaks of OPA and TPA spectra are blue-shifted, the Δ E (energy gaps between the highest occupied orbital and the lowest unoccupied orbital) increase. The different π-conjugated bridges (fluorene and pyrene) and terminal groups have slight effect on the OPA properties. Nevertheless, the molecules bearing 1,6-disubstituted pyrene as the π-conjugated bridge display the largest δ in both series of compounds 3 and 4. Moreover, the δ values of molecules with benzothiazole-substituted terminal groups are larger than those of the molecules with diphenylamine, which is attributed to benzothiazole groups stabilizing the planarity of the branch parts, extending the conjugated length and increasing the π-electron delocalized extent. Furthermore, the molecular size has marked effect on OPA and TPA properties. It is worthy to mention that cruciform 8 displays the largest δ among all the studied molecules in the range of 600-1100 nm. This research could provide a better understanding for the origin of the linear and nonlinear optical properties, and it would be helpful to gain more information about designing two-photon absorption materials with large δ. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The photophysical properties of a series of multifunctional compounds applied in organic light-emitting diode (OLED) materials have been studied by quantum chemistry. These compounds have been integrated by an electron and hole transporting component as well as an emitting component into the donor–π–acceptor (D–π–A) structures. To reveal the relationship between the structures and properties of these multifunctional electroluminescent materials, the ground- and excited-state geometries were optimized at the B3LYP/6-31G(d), HF/6-31G(d), and CIS/6-31G(d) levels, respectively. The ionization potentials and electron affinities were computed. The mobilities of hole and electron in these compounds were studied computationally based on the Marcus electron transfer theory. The maximum absorption and emission wavelengths of compounds 1– 4 were calculated by time-dependent density functional theory method. As a result of these calculations, it was concluded that the electron injections of compounds 2– 6 are much easier than Mes2B[ p-4,4′-biphenyl-NPh(1-naphthyl)] (BNPB) due to the introduction of the thiophene group, anthracene group, and N=N as a part of the π-conjugated bridge, compounds 5 and 6 can act as electron transport and hole transport materials, respectively. Compounds 1 and 2 have higher electron mobility and light-emitting efficiency as compared to compounds 3 and 4. Compounds 3 and 4 have quite longer fluorescence lifetimes than compounds 1 and 2 due to the larger Stoke’s shifts. [ABSTRACT FROM AUTHOR]

The electronic structures, charge injection and transport, absorption and emission spectra, properties of two series of fluorene-based oligomers {2-[2-{2-[5-(9H-Fluoren-3-yl)-thiophen-2-yl]-vinyl}-6-(2-thiophen-2-yl-vinyl)-pyran- 4-ylidene]-malononitrile} n (FTPM) n and {2-{2-{2-[5-(9H-Fluoren-2-yl)-2-hydroxy- 3-methoxy-phenyl]-vinyl}-6-[2-(2-hydroxy-3-methoxy-phenyl)-vinyl]-pyran-4- ylidene}-malononitrile} n (FOOPM) n ( n = 1–4) have been investigated by the density functional theory (DFT) approach. The ground-state geometries of (FTPM)4 and (FOOPM)4 optimized at B3LYP/6-31G(d) level exhibited zigzag arrangements. The energies of HOMO and LUMO, HOMO–LUMO energy gaps (Δ E H– L) of (FTPM) n and (FOOPM) n ( n = ∞) were obtained by linear extrapolation method. Moreover, the calculations of ionization potential (IP), electronic affinity (EA), and reorganization energy (λ) were used to evaluate the charge injection and transport abilities. For (FTPM)4 and (FOOPM)4, the TDDFT calculations revealed that the absorption peaks can be characterized as π–π* transition and couple with the location of electron density distribution changes in different repeat units. All the earlier theoretical investigations are intended to establish the structure–property relationships, which can provide guidance to design the organic light-emitting diodes (OLEDs) with high performance. [ABSTRACT FROM AUTHOR]

Among all the 4478 classical isomers of C66, C66( C s:0060) with the lowest number of pentagon–pentagon fusions was predicted to be the most stable isomer, followed by isomers C66( C2 v:0011) and C66( C2:0083). The infrared spectra and aromaticity of the most stable isomers were predicted. The relative stabilities of C66 isomers change with charges or doping of metals. The structures and relative stabilities of the most stable metallofullerenes were delineated and compared with experiment. Sc2@C66( C2:0083) was predicted to be the most stable metallofullerene, although Sc2@C66( C2 v:0011) was observed. Charge-transfer from Sc2 to the fused pentagons and the bonding between these two moieties significantly decrease the strain energies caused by the pair of fused pentagons thereby stabilizing the fullerene cage. [ABSTRACT FROM AUTHOR]

Among all the 4478 classical isomers of C66, C66( C s:0060) with the lowest number of pentagon–pentagon fusions was predicted to be the most stable isomer, followed by isomers C66( C2 v:0011) and C66( C2:0083). The infrared spectra and aromaticity of the most stable isomers were predicted. The relative stabilities of C66 isomers change with charges or doping of metals. The structures and relative stabilities of the most stable metallofullerenes were delineated and compared with experiment. Sc2@C66( C2:0083) was predicted to be the most stable metallofullerene, although Sc2@C66( C2 v:0011) was observed. Charge-transfer from Sc2 to the fused pentagons and the bonding between these two moieties significantly decrease the strain energies caused by the pair of fused pentagons thereby stabilizing the fullerene cage. [ABSTRACT FROM AUTHOR]