Spectroscopy of surface-enhanced Raman scattering of a complex with charge transfer between a bis-crown-containing stilbene and a bis-ammonium-alkyl derivative of dipyridylethylene

摘要

The structure of a charge transfer complex (CTC) formed by a bis-crown-containing stilbene (1) and a dipyridylethylene derivative (2) is studied by surface-enhanced Raman scattering spectroscopy. It is found that an excess of 2 leads to the formation of a 1:1 CTC structure ([1.2]), whereas an excess of 1 leads to the stabilization of a sandwichlike 2:1 CTC structure ([1.2.1]). It is also revealed that 1 and diperchlorate of 1-ammoniumpropyl-4-methylpyridinium (5) form a 1:1 CTC structure, which is much less stable. Analysis of the surface-enhanced Raman scattering data suggests that, in complete agreement with the Mulliken theory, the CTCs under study are ordinary molecular complexes in the ground state and the interaction of a molecular complex with a photon excites the former. The excitation is accompanied by a significant transfer of the electron density from the donor I to the acceptor 2 (5). The structural fragments of the molecules responsible for the intermolecular interaction and charge transfer are ascertained using model compounds. The charge transfer in donor-acceptor pairs occurs between the electronic systems of trisubstituted benzene and pyridine. A CTC of the [1.2] or [1.2.1] type contains two equivalent donor-acceptor pairs; however, only one of them is involved in the charge transfer. (C) 2004 MAIK "Nauka/Interperiodica".