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) resulting 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 monitored using the time-resolved microwave conductivity (TRMC) technique, while only very small conductivity signals are observed in the coil state. The thermochromic shift in going from the rod state at room temperature to the coil state at 65 degreesC is accompanied by a decrease in the photoconductivity. The large conductivity signal in the rod state is attributed to the formation of mobile charge carriers possibly via interchain charge transfer 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 for charge carrier formation, phi (p), and the sum of the charge carrier mobilities, Sigma mu. The decay of the photoconductivity is nonexponential and extends to microseconds.