Fluorescent gels: Immobilization of non-fluorescence molecules beyond the aggregation induced emission

Abstract

Aggregation Induced Emission (AIE) has aroused the interest of the scientific community, revealing the mechanisms behind this phenomenon. The most common ones are the avoidance of electronic couplings which could quench the emission or non-radiative deactivation through vibrational modes, intramolecular rotations, photoisomerization, etc. This type of knowledge can be applied to the rational design of molecules that are trapped in an environment that prevents those non-radiative processes. Here we present oligo(styryl)benzene and bis(styryl)-4-(dicyanomethylene)-4H-pyran molecules designed to be non-fluorescence either in solution or in the solid/aggregate state, but they reach in some cases quantum yields of 50 % and 60 % when trapped in a gel matrix. These compounds deactivate in solution by vibrational relaxation and photoisomerization, the latter favored by the incorporation of cyano groups. The complete spectroscopic characterization of the gels together with quantum chemical calculations have allowed us to explain their photophysical behavior. In addition, compounds 1 and 4 were interacted with β-cyclodextrin and bacterial DNA (plasmid pUC19). An increase in fluorescence was observed which suggests an interaction between the dye and the supramolecular structure that blocks intramolecular motions and prevents aggregation. A more selective functionalization would allow the design of more fluorescent, higher contrast and more specific sensors.