Photochemical Hole Burning and Photooptical Properties of Doped Dye Molecules in Linear Polymers

Abstract

Photochemical hole burning (PHB) is a phenomenon where a stable dip or a hole is created in the absorption spectrum of a chromophore by site-selective excitation with a narrow-band light such as a laser. The phenomenon of PHB was discovered by two Russian groups in 1974 [1, 2]. The site-selective excitation is possible when the absorption line width of each chromophore (this is called, the “homogeneous width”, Γ_h) is smaller than the width of the whole absorption band profile (called the “inhomogeneous width”, Γ_i). In such a case, the whole absorption line is called, the “inhomogeneous band”. This situation is often realized for doped dye molecules in amorphous matrices like polymers at low temperatures because the optical linewidth of each chromophore decreases drastically as temperature becomes lower and because the resonant frequency of each chrompohore in amorphous solids has an inhomogeneous distribution due to the difference in its microenvironment (Fig. 1.1). The sharp absorption line of individual chromophore at low temperatures is called the “zero-phonon line”.