Abstract
Electronic absorption and steady state and time-resolved emission spectroscopy were used to investigate the occurrence of several nonradiative processes, e.g. excitational energy transfer, photoinduced electron transfer, etc., between the electron donors p-toluidine (p-tol) and its N,N-dimethyl derivative (N,N-DM-p-tol) and the well-known acceptor dimethylterephthalate (DMTP) in solvents of different polarity at 296 K and in ethanol (EtOH) rigid glassy matrix at 77 K. From the room temperature experimental results, the strong dynamic fluorescence quenching phenomena observed for the toluidine donors in the presence of the acceptor DMTP may be due mainly to the combined effect of two non-radiative processes: (1) photoinduced electron transfer from the excited (S 1) donor to the ground state acceptor; (2) enhanced intersystem crossing (isc) within the donor as the S 1 state acquires n π * character due to conformational changes in the presence of DMTP. Lack of spectral overlap between the donor emission and acceptor absorption excludes the possibility of the occurrence of singlet-singlet Förster-type energy transfer within the reactants. In addition, no static quenching was observed. At 77 K, the isc process seems to be primarily responsible for the observed decrease in the donor fluorescence emission band in the presence of DMTP, whereas triplet-triplet (T 1 D #x02192; T 1 A energy transfer appears to be responsible for donor phosphorescence quenching.
Published Version
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