Fluorescence‐resolved hole burning of squaraine dyes in polymer matrices at low temperature

Abstract

AbstractA new technique that combines nonphotochemical hole burning with multichannel detected fluorescence line narrowing has been used to obtain vibrationally resolved fluorescence spectra of squaraine chromophores in polymer matrices at 1.4 K. At a fixed excitation frequency, the intensities of the zero‐phonon lines decay with time due to nonphotochemical hole burning, leaving behind a broader background attributed to emission from molecules excited into phonon sidebands. Subtracting the spectrum of the hole‐burned sample from the initial one leaves predominantly a zero‐phonon line excited spectrum exhibiting enhanced vibrational structure. Spectra of the same squaraine in polystyrene and polyethylene matrices show differences in the frequencies and intensities of the phonon sidebands, indicating differences in the frequencies and strengths of the matrix modes coupled to the electronic transition of the chromophore. The phonon densities of states inferred through different measurement techniques are compared and related to electronic dephasing rates.