Optical detection and probing of single dopant molecules of pentacene in a p-terphenyl host crystal by means of absorption spectroscopy

Abstract

With the use of a combination of laser frequency-modulation absorption spectroscopy and either Stark, longitudinal ultrasonic, or transverse ultrasonic internal modulation, the optical absorption spectrum of a single impurity molecule of pentacene in a p-terphenyl crystal may be measured at liquid helium temperatures. The general properties of this detection method are illustrated by first applying the technique to the detection of persistent spectral holes in the pentacene/p-terphenyl system. Selection of a single absorber for measurement is accomplished by tuning the probing laser far out into the wings of the inhomogeneously broadened 0-0 absorption lines for either the O1 or O2 sites. The single-molecule line shape is similar to that predicted by a simple model of the double-modulation process. The approximate amplitude of the single-molecule signals suggests that triplet bottleneck power broadening is suppressed far out in the wings of the inhomogeneous line. This work probes the ultimate N = 1 limit of the statistical fine structure present in all inhomogeneous absorption lines. © 1990 American Chemical Society.