Fluorescence enhancement induced by supramolecular J-aggregation of pyrene dye containing a flexible rotation group

A pyrene dye bearing a flexibly rotated hydrophobic group (3,4,5-tri(dodecyloxy)benzoyl-) was synthesized and fully characterized. In cooling processes for the dye monomer in CHCl3/CH3OH, the monomer was transformed into the J-aggregates which were characterized to possess a typically nanowired shape. A thermodynamic hysteresis of the molar fraction of the aggregates was observed explicitly between the cooling and heating processes. A pronounced self-absorption was involved in the aggregate solutions of the dye at high concentrations. Clearly, the J-aggregation conferred a few intriguing attributes such as a red-shift of maximum absorption peak, a higher quantum yield of absolute fluorescence and a shorter fluorescence lifetime than the monomer. Collectively, these attributes brought about a phenomenon of aggregation-induced emission enhancement (AIEE). In addition, the HOMO and LUMO energies were calculated by DFT for both the monomeric and aggregated states. Furthermore, the stacking parameters in the J-aggregates were evaluated according to the molecular exciton theory. It can be concluded that the J-aggregation enhanced substantially the emission of the dye. Undoubtedly, the strategy for the development of the AIEE molecules containing a flexible rotation group via J-aggregation as revealed in this work will be very useful in the future design of new organic light-emitting dyes.