HIGH-PRESSURE EFFECT ON THE TWISTED INTRAMOLECULAR CHARGE-TRANSFER FLUORESCENCE AND ABSORPTION OF PARA-N,N-DIMETHYLAMINOBENZYLIDENEMALONONITRILE (DMABMN) IN POLYMERIC MATRICES

The pressure effect on the luminescence of p-N,N-dimethylaminobenzylidenemalononitrile (DMABMN) in several solid polymer matrices has been studied. An increase of fluorescence intensity by a factor of 35 to 200 has been observed, in different polymers, within 100 kbar. Two general regions of pressure behavior are distinguished. In the first, "low pressure" region (0-25) kbar the amplification of luminescence intensity is explained by a retardation of motion (twist) in the excited state by increasing pressure. The generalized volume change "DELTAV" for this process has been obtained as a function of pressure and could be predicted from the kinetic model proposed. The polarity and free volume effects are discussed. The free volume concept is found not to provide a satisfactory quantitative description for the pressure dependence of the rearrangement. In the "high pressure" region (> 50 kbar) where intensity decreases to a different degree in different polymers the contribution of the nonradiative rate from the originally excited state is considered.