Abstract

Photoconductivity in polynuclear aromatic hydrocarbons and straight-chained polyenes has been known for some time.^{1, 2} At room temperature and in the dark these compounds are all insulators; however, under the illumination of a bright light source (e.g., a laser), they become semiconductors. Polynuclear aromatics have been investigated as likely photoconductors because of their molecular geometry and electronic structure. The planar molecules crystallize so that some interaction between the pi-orbitals in the rings of adjacent molecules occurs. Charge carriers therefore can hop between adjacent molecules via the pi-orbitals. Straight chain polyenes, such as beta-carotene, are also photoconductors because of their geometries. The long conjugated backbone allows conduction of charge carriers along its length. The photoconductive behavior of carotenoids is believed to be involved in photosynthesis and vision. The light sources used in early studies were flashlamps or tungsten filament lamps and the currents produced were very small, i.e. on the order of picoamperes.

© 1987 Optical Society of America