THE TEMPERATURE-DEPENDENCE OF THE FLUORESCENCE LIFETIMES OF THE ION-PAIRS OF ALPHA,OMEGA-DIPHENYLPOLYENYLIC CARBANIONS

The alkali metal salts of the alpha,omega-diphenylpolenylic carbanions exist in ether and amine solutions as mixtures of tight and loose ion pairs which differ in their absorption and emission spectra. Fluoresc ence lifetimes were determined using pulsed radiation from the Daresbu ry synchrotron in conjunction with single photon counting and were fou nd to increase towards limiting values on cooling the solutions. Analy sis shows that this behaviour is in consonance with a mechanism in whi ch the excited state is deactivated by fluorescence and non-radiative decay in competition with activated skeletal twisting about a polyenyl ic bond. The Arrhenius parameters have been determined for the loose i on pairs of a variety of systems but those of the tight ion pairs have proved to be less accessible. In certain cases the spectral changes a rising from photoisomerisation and the subsequent ground state relaxat ion could be recorded.