Elena Marri

Effect of the nature of aryl and heteroaryl groups on the excited state properties of asymmetric 1,4-diarylbutadienes

Abstract The excited state properties of a series of asymmetric 1-Ar,4-phenylbutadienes (Ar=naphthyl, phenanthryl, anthryl, pyrenyl, pyridyl and thienyl) have been investigated by stationary and pulsed techniques with the main aim of assessing the effect of the nature and size of the Ar group on the photophysical and photochemical behaviour. The comparison of the present results with those of previous studies on the corresponding 1,2-diarylethenes shows how the extension of the unsaturated chain affects the excited state properties and opens alternative adiabatic and “one photon–two bonds” isomerization mechanisms. The role of the relative position of the L a and L b states of Ar with respect to the olefinic B u state on the photobehaviour is discussed.

Effect of solvent polarizability on dual fluorescence of EE-1-phenyl,4-(1′-pyrenyl)-1,3-butadiene

Abstract The properties of the lowest excited states of EE -1-phenyl,4-(1′-pyrenyl)-1,3-butadiene were studied by absorption and emission spectrometry in solvents of different polarity and polarizability. The effect of the latter on the energy and relative position of the two lowest excited singlet states (of B u and A g parentage) was investigated. Dual fluorescence was observed in low polarizability solvents at room temperature. The emission from a thermally populated upper state disappears at low temperature and in higher polarizability solvents, such as CS 2 , where the lowest excited state acquires an allowed character. The excited molecule relaxes mainly by the radiative pathway. Internal conversion also plays an important role while the triplet population is scarce and photoisomerization is practically negligible. The behaviour is compared with those of related compounds.

Isotopic and chemical dilution effects on the vibrational relaxation rate of some totally symmetric motions of liquid acetonitrile

Abstract The vibrational dephasing of the ν 1 (C–H, C–D stretching) and ν 3 (C–H, C–D bending) symmetric motions of liquid acetonitrile in its light and fully deuterated forms has been studied in the frame of the vibrational time correlation functions obtained as Fourier transforms of the isotropic Raman spectral distributions and interpreted within the Kubo theory. In addition, the experimental isotropic profiles have been analysed within the bandshape approach formulated by analytical Fourier transformation of the Kubo vibrational time correlation functions in order to derive the relaxation parameters in the frequency domain. The effects of the isotopic (CH 3 CN/CD 3 CN and vice versa) and chemical (CCl 4 ) dilution on the bandshapes and on the vibrational relaxation parameters have been studied. It was observed that the decay rate of ν 1 mode is insensitive to the isotopic dilution but varies appreciably with chemical (CCl 4 ) dilution. The vibrational dephasing of ν 3 mode is qualitatively, but not quantitatively, affected in the same way by chemical dilution and shows a slower modulation regime than that exhibited by the stretching mode. Unlikely from the latter, the ν 3 mode results are slightly affected by the isotopic dilution. Phase relaxation mechanisms of these two motions of acetonitrile in the liquid state are proposed on the basis of these data, and a comparison is made with the results earlier published.

Photoisomerization mechanisms and photoselectivity of the stereoisomers of 1-(pyrid-n-yl),4-phenylbuta-1,3-diene

The positional isomers of 1-(pyrid-n-yl),4-phenylbuta-1,3-diene (n = 2, 3 and 4) have been synthesized and characterized by spectrometric techniques.All the four expected stereoisomers (EE, EZ, ZE and ZZ) were prepared for n = 2 while only three and two geometrical isomers were obtained for the positional isomers with n = 3 and 4, respectively. Their excited state properties were investigated by stationary and pulsed fluorimetric techniques and by laser flash photolysis. This paper describes the photochemical behaviour under direct and triplet sensitized excitation. The selective formation of photoproducts and the role of diabatic/adiabatic mechanisms are reported and compared with the results on the direct photoisomerization of the EE and ZE isomers in the singlet manifold described in a previous paper (G. Bartocci, G. Galiazzo, U. Mazzucato and A. Spalletti, Phys. Chem. Chem. Phys., 2001, 3, 379–386).

Photobehaviour of di(phenylbutadienyl)arenes containing nitrogen and sulfur heteroatomsElectronic supplementary information (ESI) available: calculated electronic spectra (transition energy and oscillator strength) and heats of formation in the ground state of the elongated and compressed conformations of the investigated compounds. See http://www.rsc.org/suppdata/pp/b3/b309267d/

The photophysics and photochemistry of 1,4- and 1,3-di(phenylbutadienyl)benzene, and two analogues of the latter where the central benzene ring has been replaced by pyridine and thiophene rings, have been studied. The combined effects of the heteroatoms, the length of the olefin chains and the type of conjugation on the photobehaviour have been determined and compared with results previously obtained for the corresponding ethene derivatives. The conformational equilibria were investigated by selective photoexcitation: in the case of the 1,3 hydrocarbon and the pyridine analogues, the spectral properties of two rotamers are reported.