Concentration Effects on Spectra and Persistent Hole-Burning of Porphyrin Doped Langmuir-Blodgett Films

Abstract

Persistent spectral hole-burning has recently been employed in investigations of pseudo-two-dimensional systems such as porphyrin and organic dye doped Langmuir-Blodgett films [1]. In order to perform spectral measurements on such ultra-thin materials, especially in the case of monolayers, the necessity to work with highly concentrated samples arises. For example, in a spectral hole-burning study of porphyrin centres in a multilayer assembly [2], the average distance between chromophores was about 3.5 nm which is of the same order as the Forster radius for energy transfer. Energy transfer and aggregation of impurities at high concentrations may strongly interfere with other processes under investigation such as optical dephasing and spectral diffusion. The effect of impurity concentration on spectral properties is an effective way of determining the dominant processes. Some data has already been published for conventional bulk systems such as tetracene doped alcohol glass [3] and chlorin and tetraphenylporphyrin doped polystyrene [4]. Here we present results of investigations of concentration effects on spectra and hole-burning of impurity doped Langmuir-Blodgett films.