Fluorescence of molecular micro- and nanocrystals prepared with Bodipy derivatives

Trimesitylbodipy (TMB), a new 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene derivative with bulky side groups, was synthesized in order to develop nanostructured fluorescent devices. Fluorescence properties of TMB were studied in dichloromethane, in amorphous films prepared by rapid evaporation of a solution and in micro- and nanocrystals. It was compared to the spectroscopy of Mesitylbodipy (MB) to see if the mesityl groups of TMB modify fluorescence in the solid state. A set-up including a space and time correlated photon-counting photo-multiplier was used to record fluorescence intensity and lifetime images of solids. For both dyes, the formation of fluorescent excimers was observed. There is evidence to suggest energy transfer from monomer to both fluorescent and non-fluorescent excimers. MB fluorescence is still quenched in the crystalline state but in TMB monocrystals the fluorescence comes from only one excimer with a lifetime of 9.5 ns. TMB nanocrystals with a monoexponential fluorescence decay were also prepared.