Dynamics and vibrational spectra of individual molecules in polymer glasses

Abstract

Fluorescence excitation and vibrationally resolved dispersed fluorescence spectra of single molecules of terrylene in a polyethylene matrix at 1.5 K are presented. Single molecules are selected from the inhomogeneous ensemble by tuning a narrow-band dye laser into resonance with the sharp electronic origin features in highly dilute samples. Total fluorescence is detected with a photomultiplier and photon counting electronics, while vibrationally resolved fluorescence spectra are obtained by dispersing the emission onto a CCD detector. The excitation spectra reveal a variety of spectral diffusion effects on a wide range of time scales, including both continuous wandering over a range of frequencies and jumping among two or more discrete resonance frequencies. The dispersed fluorescence spectra show two distinct types of vibrational frequency and intensity patterns, possibly arising from terrylene molecules in the amorphous and crystalline regions of the polyethylene matrix, respectively. The description of the emission as resonance Raman or fluorescence is discussed.