MICROFLUORESCENCE AND MICROSTRUCTURE OF TETRACENE AGGREGATES IN POLY(METHYL METHACRYLATE)

Polymer films of tetracene doped into poly(methyl methacrylate) (PMMA) were studied by macroscopic and microscopic spectroscopy. Tetracene forms aggregates in PMMA. The size of the aggregates and the degree of the aggregation increase with concentration. Microscopic measurements demonstrate that different aggregates show different morphologies and luminescence, indicating different structural formations. The global fluorescence spectra and fluorescence excitation spectra for different concentrations of tetracene (doped into poly(methyl methacrylate)) have been monitored in the temperature range of 77-298 K. As the temperature increases, the emission peaks shift gradually to longer wavelength. The fluorescence excitation spectra at 77 and 298 K result from the site with the same environment. The experimental results demonstrate that no phase transition is observed in the tetracene/PMMA system with decreasing temperature, in contrast to the case of tetracene single crystals. A comparison is also made between PMMA embedded tetracene crystallites and free crystallites. The potential of the newly developed near-field scanning optical spectroscopy techniques is demonstrated.