In Situ Fluorescence Observation of the Vacuum-Deposition Process of 1,3-Di-N-carbazolylpropane and Morphological Characteristics of the Deposited Film

The deposition processes of 1,3-di-N-carbazolylpropane (DCzP) have been investigated by measuring in situ fluorescence spectra during deposition on hydrophilic and hydrophobic quartz substrates. Excimer fluorescence was observed even at the initial stage of deposition, and its intensity ratio to monomer fluorescence changed with the progress of deposition, depending upon the nature of the substrate and the temperature. The deposition process of DCzP on hydrophilic substrates consisted of four stages, whereas three stages were observed for deposition on hydrophobic substrates. The fluorescence spectrum of the deposited DCzP film consisted of monomer, partial overlap excimer, and sandwich excimer fluorescence and was different from that of an amorphous DCzP film prepared by fast evaporation of the solvent. Fluorescence and optical microscopies of deposited films were performed after taking the films out of the vacuum chamber. The deposited molecules formed aggregates on the substrates which were initially spherical but which changed to a fractal-like shape after having been stored in a desiccator. The initial aggregates were amorphous, but the fractal-like aggregates were crystalline. These behaviors were compared with the results of meso-2,4-di-N-carbazolylpentane presented in our previous work and discussed in terms of interactions between the substrate and the compound and difference in a conformational distribution between these bichromophoric compounds.