Effect of remotely connected trialkyl ammonium groups on the dye molecules in the photochemical behavior on the clay nanosheet.

Abstract

The enhanced emission properties of several cationic dye molecules on the clay surface established as a result of the strong electrostatic interaction and associated molecular flattening leading to either the suppression of non-radiative deactivation processes or the improvement of radiative deactivation processes has been verified, and it is known as surface-fixation induced emission (S-FIE). Here, the differences in the S-FIE properties as well as the self-fluorescence quenching behavior of the dimidium and propidium dyes were compared. Propidium differs from dimidium by the substitution of a propyl (diethyl methylammonium) group at the 5th position instead of the methyl group in dimidium. So, the differences induced by this substitution, which is not even in conjugation with the chromophore part of the dye molecule show a significant impact on the adsorption strength, S-FIE properties, and self-fluorescence quenching behavior. In propidium and dimidium, the suppression of k_nr was the key factor for emission enhancement on the clay surface. Interestingly, the alkylammonium cation group in the Propidium helped for better adsorption strength as well as to reduce the self-fluorescence quenching behavior on the clay surface as compared to the dimidium. Since the trialkylammonium cation was not in conjugation with the core structure of the molecule and located at a specific distance, it did not interrupt the flattening of the molecule on the clay surface. These results could be beneficial in the construction of efficient photochemical reaction systems, where the molecule having low adsorption strengths can be modified by alkyl ammonium cations, which will not affect molecular planarization.