Influence of backbone conformation on the photoconductivity of polydiacetylene chains

The thermochromic, solvatochromic, and photoconductive properties of 3-, 4- , 6-, and 9-BCMU (BCMU = poly(butoxycarbonylmethylurethane)-diacetylenes) r esulting from changes from rod (red or blue) to coil (yellow) conformations of the polymer backbone have been studied. Photoexcitation of solutions of BCMUs in the rod state results in a large transient photoconductivity as m onitored using the time-resolved microwave conductivity (TRMC) technique, w hile only very small conductivity signals are observed in the coil state. T he thermochromic shift in going from the rod state at room temperature to t he coil state at 65 degreesC is accompanied by a decrease in the photocondu ctivity. The large conductivity signal in the rod state is attributed to th e formation of mobile charge carriers possibly via interchain charge transf er within aggregates. Values from 0.8 x 10(-4) to 3 x 10(-4) cm(2) V-1 s(-1 ) are found for the lower limit to the product of the quantum efficiency fo r charge carrier formation, phi (p), and the sum of the charge carrier mobi lities, Sigma mu. The decay of the photoconductivity is nonexponential and extends to microseconds.