No abstract

The shapes of the fluorescence emission and lowest excited singlet-state absorption spectra of all-trans-1,4-diphenylbutadiene (DPB) in hydrocarbon solvents vary with excitation wavelength when exciting on the extreme red edge of the ground-state absorption spectrum. This contrasts with the wavelength independence observed for the excited singlet-state absorption and fluorescence emission spectra of 1,5-diphenyl-2,3,4,6,7,8-hexahydronaphthalene and for the fluorescence emission spectra of 1 ,Cdiphenyl-1,3-~yclopentadiene, s-trans and s-cis structural analogs of DPB, respectively. The spectral changes in DPB can be explained in terms of an excitation wavelength-dependent production of s-cis and s-trans rotamer populations in the excited state. The DPB fluorescence emission spectrum was resolved into s-cis and s-trans components. The vibronic structure of the s-cis fluorescence spectrum is similar to that of s-trans, but the band origin is red-shifted and there is a slightly larger amplitude on the red edge. The excited-state absorption spectrum of s-cis DPB appears to be red-shifted relative to that of s-trans DPB as well.

Resonance Raman and absorption spectroscopy of the lowest triplet state of 1,3,5-hexatriene and deuteriated derivatives at 183 K : molecular structure in the T1 state Langkilde, F.W.; Wilbrandt, R.; M?ller, S.; Brouwer, A.M.; Negri, F.; Orlandi, G. Published in:Journal of Physical Chemistry DOI:10.1021/j100171a028Link to publication Citation for published version (APA):Langkilde, F. W., Wilbrandt, R., M?ller, S., Brouwer, A. M., Negri, F., & Orlandi, G. (1991). Resonance Raman and absorption spectroscopy of the lowest triplet state of 1,3,5-hexatriene and deuteriated derivatives at 183 K : molecular structure in the T1 state. Journal of Physical Chemistry, 95, 6884-6894. DOI: 10.1021/j100171a028 General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Time-resolved resonance Raman (RR) spectra of the lowest excited triplet state TI of (E)-1,3,5-hexatriene, (E)-3-deuterio-l,3,5-hexatriene, and (E)-l,l-dideuterio-l,3,5-hexatriene are obtained at 183 K. The TI potential energy surface (PES), determining energy minima, equilibrium geometries, frequencies, and normal modes of vibration, is calculated, and RR intensities are obtained on the basis of the Franck-Condon mechanism. By comparison with the calculated spectra, the observed RR spectra are assigned to an equilibrium mixture of planar E and Z species in the TI state. The relative intensity of the E and Z bands at temperatures between 293 and 183 K gives an upper limit of 0.22 kcal/mol for the energy difference between the planar E and 2 forms. Time-resolved triplet-triplet absorption measurements as a function of temperature between 296 and 183 K yield a frequency factor A of 1.6 X lo7 s-I and an apparent activation energy E, of 0.7 kcal/mol for the decay of the TI state. Consequently, an upper limit of 0.7 kcal/mol above the planar E and 2 geometries is established for the possible local energy minimum at the twisted geometry. On the basis of these data, a PES is proposed for the TI state of 1,3,5-hexatriene with respect to torsion around the central CC bond and the C2C3 and C4Cs bonds.

Lowest excited triplet state of 2,5-dimethyl-1,3,5-hexatriene : resonance Raman spectra and quantum chemical calculations Negri, F.; Orlandi, G.; Brouwer, A.M.; Langkilde, F.W.; M?ller, S.; Wilbrandt, R. General rights It is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Theoretical and Raman spectroscopic studies are presented of the ground and lowest excited triplet states of (E)-and (Z)-2,S-dimethyl-l,3,S-hexatriene and their 3,4-dideuterio and 3-deuterio isotopomers. The TI potential energy surface is calculated from SCF-LCAO-MDCI theory. Energy minima and equilibrium geometries are determined in the TI state. Frequencies and normal modes of vibrations are calculated for the minima of the TI and S, states. Energies of higher triplet levels are computed and oscillator strengths for the TI -T, transitions are determined. The displacements in equilibrium geometries between the TI and the T, level corresponding to the strongest TI -T, transition are calculated and are used to estimate the intensities of the resonance Raman spectra of the TI state under the assumption of a predominant Franck4hndon scattering mechanism. The influence of the ground-state conformation around C-C single bonds on TI resonance Raman spectra is considered in detail for the two isomers. It is found that for the E isomers the tEt and for the Z isomers the tEc forms are the predominant ones in the TI state. The 2 forms are at considerable higher energy than the E forms in the TI state due to nonbonded interaction. A good agreement is found between theoretically calculated and experimental spectra. The results are compared with previously published data for 1,3,S-hexatriene. Iatroductioawe considered the transient resonance Raman (TRR) spectra of 1,3,5-hexatriene (HT) in its TI state with the purpose of obtaining information about the geometry of the TI intermediate and about the mechanism of the cis-trans photoisomerization in TI. The experimental TRR spectra, which have been found to be identical in experiments on solutions of either of the two ground-state isomers, were interpreted by quantum mechanical calculations of equilibrium geometries and vibrational frequencies at the trans (E), cis ( Z ) , and centrally twisted (P) geometries in TI and in the T, state responsible for the TRR activity. On the basii ...

1994luminescence, fluorescence luminescence, fluorescence (organic substances) K 2540 -016Excited State Spectra and Dynamics of Phenyl-Substituted Butadienes.-The results for the compounds (I)-(III) reveal different electronic properties and excited-state dynamics for structurally similar systems. -(WALLACE-WILLIAMS, S. E.; SCHWARTZ, B. J.; MOELLER, S.; GOLD-BECK, R. A.; YEE, W. A.; EL-BAYOUMI, M. A.; KLIGER, D. S.; J. Phys. Chem. 98 (1994) 1, 60-67; Dep. Chem. Biochem., Univ. Calif., Santa Cruz, CA 95064, USA; EN)