Photogeneration of charge carriers in acetylenic polymers and its sensitization by dyes

A significant inner photoeffect in organic polymers with triple bonds R+CCR1CC+nR, and the metal polyacetylenides RCCM has been found and investigated by means of direct-current photoconductivity and photoelectromotive force in intermittent light. The dependence of the photocurrent on the light intensity can be expressed by the equation iph ≐ αLn, where 0.5 < n < 1. The photocurrent relaxation in the range of 10−5 sec. to several minutes displays a second-order process. Ohm's law is not obeyed. The absorption spectra have been compared with those of photoconductivity, photoelectromotive force, and luminescence. Preliminary short-ultraviolet irradiation increases the photosensitivity; this is ascribed to bond rupture and electron-trapping. The latter is confirmed by ESR measurements. Upon evacuation the dark conductivity and the photoconductivity are increased by 3 and 2 orders of magnitude, respectively, and the photoelectromotive force by 5. Oxygen and water vapor reversibly depress the dark and photoconductivity. A photodesorption of oxygen from the surface of metal polyacetalinide can be surmised. Electron acceptors (quinone, chloranil) and mercury vapor have a significant influence on the semiconduction. The photoeffect in the polymers can be spectrally sensitized by various adsorbed dyes. The proper sensitivity is equally changed on dye adsorption. The mechanism of the effects observed is discussed.