The photophysics of simply substituted styrenes

Crosby, Paul Maurice (1979) The photophysics of simply substituted styrenes. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

This thesis documents a study of the photophysics of a series of substituted styrenes, using fluorescence intensity and fluorescence lifetime measurements. The construction of the spectrofluorimeter and time correlated single photon counting apparatus used for this work is briefly described. A comparison and rationalization of the non radiative decay in a series of compounds is presented with reference to benzene and stilbene. It is concluded that the planarity of the ground state molecule with respect to the aromatic ring and olefinic double bond is the most critical factor contributing to the nonradiative rate, and that those compounds which are not planar in the ground state undergo a marked solvent enhanced non radiative decay process. Molecular orbital calculations using PPP, CND0/2 and two different UNDO/S parameterizations have been carried out to simulate the absorption spectra and to construct a potential energy surface for geometric isomerization. A comparison of theoretical and experimental values for the triplet energy levels is given and a theoretical basis determined for an empirical relationship between the energy levels of S2 and T1. The differences in the potential energy surfaces for CNDO/S, PPP and CNDO/2 have been examined and the shortcomings of the spectroscopic parameterizations in predicting ground state functions are discussed. An amalgamation of CNDO/S transition energies with 3a CNDO/2 type ground state is used to describe the potential energy surfaces for geometric isomerization. It is shown that isomerization can proceed via the first triplet state or the first singlet state and that the latter involves the crossing of a small potential energy barrier.The quenching of the first excited singlet state of trans- p -methylstyreneby triethylamine and oxygen has been investigated. The temperature dependence of quenching exciplex formation and exciplex fluorescence for the trans- p - methylstyrene - triethylamine exciplex has been studied. The relative quenching of both the fluorescence and geometric isomerization of trans- p - methylstyrene has been investigated for both oxygen and triethylamine; and in the case of triethylamine isomerization via the exciplex is postulated.

This record has no associated files available for download.