Spectroscopic Study of Aggregation of Carbazole Units.

Several fluorescence spectral features in aggregation of carbazole unites have been reported in previous study. Unfortunately, the influence of inner filter effect has not been paid enough attention. In this work, aggregation of carbazole unites resulting from increasing concentration or decreasing solvent affinity, was investigated by fluorescence spectroscopy. Through comparison between the spectra of two aggregation processes, it is found that only intensity ratio of 0-0 transition to 0-1 transition in excitation/emission spectra is sensitive to aggregation states. There is an obvious decrease in that intensity ratio upon aggregation. On the other hand, other spectral features observed in previous research such as intensity decrease in S0 → S2 transition and emission quenching in concentration induced aggregation process, should be induced by inner filter effect. Graphical Abstract.