Fluorescence enhancement of benzimidazolium derivative on clay nanosheets by surface-fixation induced emission (S-FIE)

The photophysical behaviors of benzimidazolium derivative [4-(1,3-dimethylbenzimidazol-3-imu-2-yl)-N, N-diphenylaniline (2-(4-(diphenylamino)phenyl)-1,3-dimethyl-1H-benzo[d]imidazol-3-ium)] (BID) in water, organic solvents and on synthetic saponite were investigated. The fluorescence quantum yield (Φ_f) of BID was 0.91 on the saponite surface under the optimal condition, while that in water was 0.010. Such fluorescence enhancement on the inorganic surface is called “surface-fixation induced emission (S-FIE)”. This fluorescence enhancement ratio for BID is significantly high compared to that of conventional S-FIE active dyes. From the values of Φ_f and the excited lifetime, the non-radiative deactivation rate constant (k_nr) and radiative deactivation rate constant (k_f) of BID on the saponite surface and in water were determined. Results showed that the factors for fluorescence enhancement were both the increase of k_f and the decrease of k_nr on the saponite surface; especially, k_nr decreased by more than two orders due to the effect of nanosheets.

The fluorescence quantum yield increased approximately 90 times by the addition of clay.