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The polarized optical absorption spectra of different quaterthiophene single crystals in the energy region of the exciton bands originating from the first molecular transition are reported as measured in the temperatures ranging from 7 to 140 K. The intrinsic higher mobility of the b-polarized 0-0 au exciton both with respect to its replicas and to the a-polarized structures is demonstrated in high quality crystals at the lowest temperatures. The influence of structural disorder on mobility is discussed considering, for the different samples, the measured lineshape and linewidth of the absorption peaks, and the relative lineshift and intensity ratio between the 0-0 au line and its first replica at the lowest temperature. The influence of dynamic disorder is discussed considering the lineshape and linewidth of the measured peaks as a function of temperature for both polarizations in the framework of the exciton-phonon coupling theory. [ABSTRACT FROM AUTHOR]

Abstract: The ground state geometric, electronic structure and Raman spectra of 5,15-diphenylporphine (H2DPP) have been studied using B3LYP/6-31G(d) method and compared with that of well-studied free base porphine (H2P) and meso-tetraphenylporphine (H2TPP). Calculation shows that 5,15-substitution causes remarkable in-plane distortion, whereas the resulting out-of-plane distortion is negligible. The calculated electronic structure of H2DPP is consistent with the absorption spectra compared with H2P and H2TPP. The calculated vibrational frequencies of H2DPP scaled with a single factor of 0.971 agree well with experimental data (the rms error is 8.0cm−1). The assignment of experimental Raman bands of H2DPP was discussed on the basis of theoretical calculation and the comparison with that of H2P and H2TPP. The splitting of some vibrational modes involving the motion of Cm atom, such as ν 1, ν 8, and ν 10, was observed and was attributed to the diversification of the environment around Cm atoms. As the shift of absorption peaks, the shift of some structure-sensitive Raman bands of H2DPP form that of H2TPP and H2P was attributed to the in-plane nuclear reorganization (IPNR) induced by phenyl-substitution, though the contribution of nonplanarity mechanism could not be excluded completely. [Copyright &y& Elsevier]

A series of 4′-tolylterpyridyl platinum(II) complexes with different arylacetylide ligands, namely, phenylacetylide, 4-bromophenylacetylide, 4-nitrophenylacetylide, 4-methoxyphenylacetylide, 4-dimethylaminophenylacetylide, 1-naphthylaoetylide, and 3-quinolinylacotylide, were synthesized. Their photophysical properties, such as electronic absorption spectra, emission characteristics at room temperature and 77 K, and transient difference absorption spectra, have been investigated. All of these complexes exhibit a metal-to-ligand charge-transfer (1MLCT) transition at ca. 420–430 nm in their electronic absorption spectra. For ttpy-Ph, ttpy-C6H4Br-4, ttpy-C6H4OCH3-4, ttpy-C6H4N(CH3)2-4, and ttpy-Np, an additional solvatochromic charge-transfer band appears at ca. 460–540 nm. This band is sensitive to the para substituents on the phenylacetylide ligand and is tentatively assigned to a metal- or/and acetylide-to-terpyridyl charge-transfer transition (i.e., a 1MLCT or/and 1LLCT transition). All of the complexes exhibit room- temperature phosphorescence. The emission can be attributed to a 3MLCT state except for ttpy-C6H4NO2-4, for which the emission likely originates from an intraligand 3π,π∗ state involving the nitrophenylacetylide ligand. For ttpy-C6H4OCH3-4, ttpy-C6H4N(CH3)2-4, and ttpy-Np, there probably is more than one low-energy state in close energy proximity, resulting in multiple exponential decays. In addition, the triplet transient absorption difference spectra of ttpy-Ph, ttpy-C6H4Br-4, ttpy-C6H4NO2-4, and ttpy-Quin exhibit moderately intense, broad absorption bands in the visible region and extending into the near-IR region, which likely originate from the same excited state that emits or from a state that is in equilibrium with the emitting state. It appears that the electron-rich arylacetylide ligands, especially 4-methoxyphenylacetylide and 4-dimethylaminophenylacetylide, cause a decrease of the emission efficiency and disappearance of the transient absorption. In contrast, the complexes that exhibit positive absorption bands in the visible spectral region of the triplet transient difference absorption spectra show substantial optical limiting for nanosecond laser pulses at 532 nm. [ABSTRACT FROM AUTHOR]

Abstract: The title compound, 2,3-diketo-benzopiperazine, has been synthesized and characterized by elemental analysis, IR, electronic spectroscopy and single crystal X-ray diffraction. Ab initio calculations of the structure, natural bond orbital, topological analysis and thermodynamic functions of the title compound were performed at HF/6-311G** and B3LYP/6-311G** levels of theory. Vibrational frequencies were also predicted, assigned, compared with the experimental values, and they supported each other. Electronic absorption spectra were calculated by the time-dependent density functional theory, which indicates that the two absorption bands are mainly derived from the contribution of bands π→π*. The calculation of the second order optical non-linearity was carried out, and the molecular hyperpolarisability was 3.282×10-30esu. [Copyright &y& Elsevier]