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Q Bands (q + bands)
Selected AbstractsTime-dependent density functional calculations of the Q-like bands of phenylene-linked free-base and zinc porphyrin dimersINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 3 2001Yoichi Yamaguchi Abstract Time-dependent density functional theory (TDDFT) calculations have been performed on the excitation energies and oscillator strengths of the Q-like bands of three structural isomers of phenylene-linked free-base (FBP) and zinc (ZnP) porphyrin dimers. The TDDFT calculated results on the low-lying excited states of the reference monomers, FBP and ZnP, are in excellent agreement with previously calculated and experimental results. It is found that the 1,3- and 1,4-phenylene-linked dimers have monomerlike Q bands that are slightly red-shifted compared to the monomers and new Q, bands comprised of the cross-linked excitations from the FBP (ZnP) ring to the ZnP (FBP) ring at considerably lower energies than the monomer Q bands. For the 1,2-phenylene-linked dimer, the direct ,,, interaction between porphyrin rings caused by the van der Waals repulsion between them provides strong mixing of the Q, bands with the Q bands, which causes its minimum excitation energy to be red-shifted by 0.05 eV compared to the other isomers. The oscillator strengths of the Q, bands are also unexpectedly found to be as strong as those of the Q bands in the dimers. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem 84: 338,347, 2001 [source] A dual-level state-specific time-dependent density-functional theoryJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 8 2008Seiken Tokura Abstract A highly efficient new algorithm for time-dependent density-functional theory (TDDFT) calculations is presented. In this algorithm, a dual-level approach to speed up DFT calculations (Nakajima and Hirao, J Chem Phys 2006, 124, 184108) is combined with a state-specific (SS) algorithm for TDDFT (Chiba et al., Chem Phys Lett 2006, 420, 391). The dual-level SS-TDDFT algorithm was applied to excitation energy calculations of typical small molecules, the Q bands of the chlorophyll A molecule, the charge-transfer energy of the zincbacteriochlorin,bacteriochlorin model system, and the lowest-lying excitation of the circumcoronene molecule. As a result, it was found that the dual-level SS-TDDFT gave correct excitation energies with errors of 0.2,0.3 eV from the standard TDDFT approach, with much lower CPU times for various types of excitation energies of large-scale molecules. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2008 [source] Vibrational analysis of Ni(II)- and Cu(II)-octamethylchlorin by polarized resonance Raman and Fourier transform infrared spectroscopyJOURNAL OF RAMAN SPECTROSCOPY, Issue 6-7 2001Robert J. Lipski We measured the polarized resonance Raman spectra of Cu(II)-2,2,7,8,12,13,17,18-octamethylchlorin in CS2 at various excitation wavenumbers in a spectral region covering the Qy, Qx and Bx optical absorption bands. Additionally, we measured the FTIR-Raman spectrum of the highly overcrowded spectral region between 1300 and 1450 cm,1. The spectral decomposition was carried out by a self-consistent global fit to all spectra obtained. The thus identified Raman and IR lines were assigned by comparison with the resonance Raman spectra of Cu(II)-octaethylporphyrin, by utilizing their depolarization ratio dispersions and by a normal mode analysis. The latter was based on a modified transferable molecular mechanics force field of Ni(II)-octaethylporphyrin [E. Unger, M. Beck, R.J. Lipski, W. Dreybrodt, C.J. Medforth, K.M. Smith and R. Schweitzer-Stenner, J. Phys. Chem. B103, 10229 (1999)]. A comparison of normal mode patterns obtained for Cu(II)-octamethylchlorin and Cu(II)-octaethylporphyrin revealed that some modes are significantly distorted by the reduction of the pyrrole ring, in accordance with results which Boldt et al. reported earlier for Ni(II)-octaethylchlorin [N.J. Boldt, F.J. Donohoe, R.R. Birge and D.F. Bocian, J. Am. Chem. Soc.109, 2284 (1987)]. In contrast to conclusions drawn from this study, however, the results of our vibrational analysis and several further lines of evidence suggest that the normal modes of corresponding chlorines and porphyrins are still comparable, because they display contributions from the same local coordinates. Thus, the classical normal mode classification developed for metalloporphyrins is also applicable to metallochlorins. Finally, we performed a preliminary analysis of the absorption spectrum and the resonance excitation profiles and depolarization ratio dispersions of some Raman lines. The results show that the electronic properties of Cu(II)-octamethylchlorin can still be described in terms of Gouterman's four orbital model [M. Gouterman, J. Chem. Phys.30, 1139 (1959)]. In regions of the Q bands, Raman scattering of A1 modes is determined by interferences between Franck, Condon coupling and interstate Herzberg, Teller coupling between Qx(Qy) and Bx(By) states. The B2 modes are resonance enhanced by Herzberg, Teller coupling between Qx and Qy and between Qx(Qy) and By(Bx). Franck, Condon coupling of A1 modes with large contributions from C,Cm stretching vibrations is comparatively strong for Qx. This is interpreted as reflecting the expansion of the chlorin macrocycle by an electronic transition into this excited state. Copyright © 2001 John Wiley & Sons, Ltd. [source] The Origin of the Halogen Effect on the Phthalocyanine Green PigmentsCHEMISTRY - AN ASIAN JOURNAL, Issue 6 2010Uck Lee Dr. Abstract The structure and the electronic and optical properties of halogenated copper-phthalocyanine (n,,m,(Hal)-CuPc) molecules are investigated, according to the variation in the substituted halogen-atom species (Hal=Cl or Br) at the , and , positions of isoindole ring with different numbers (n and m=0, 4, 8, or 16). Our results show that the halogen effect mainly results from a structural deformation rather than caused by electronic effects. A nonplanar deformation of the phthalocyanine chromophore of the n,,m,(Hal)-CuPc molecule causes a significant change only in the HOMO and HOMO-1 levels, rather than in the LUMO levels, which leads to the appearance of a green color arising from the large red-shifts of the Soret and Q bands. The present result may serve as an important reference point for designing novel halogen-free green pigments, in accordance with the environmental regulations for the restriction of hazardous substances (RoHS) in electronic and electrical devices. [source] | ||||||||||