Absorption and fluorescence properties of bifluorene crystal and microcrystals

Optical properties of 2, 2'-(9, 9-dihexyl) bifluorene bulk crystal and microcrystals embedded in thin sol-gel films are reported. Reflection spectroscopy and Kramers-Kronig analysis are used to derive the absorption spectrum of the bulk crystal. The absorption and emission spectra obtained for the bulk crystal, microcrystals and molecules in dilute solution are very similar. Due to the perpendicular arrangement of molecules in the crystal structure, intermolecular interactions in the crystal phase are weak and have no significant effect on the electronic transitions of luminescent dye. Thus, the crystal phase has a high blue fluorescence efficiency and appears to provide the basis for a convenient approach to overcoming the aggregation tendency that degrades the electroluminescence properties of fluorene-based oligomers and polymers.