From Aqueous Solution to Langmuir–Blodgett Films: Tuning the Excimer-Coupled Aggregation-Induced Emission Behavior of Pyrene-1-carboxaldehyde

Aggregation-induced enhancement of emission (AIE) research is of particular interest to the scientific community, as it bridges material and molecular science. Derivatives of pyrene have been extensively studied for their remarkable AIE properties. However, pyrene-1-carboxaldehyde (<b>Py-CHO</b>), a frequently used precursor to construct pyrene, has not been studied extensively to explore its potential as an AIEgen, if any. In the current work, a comprehensive steady-state and time-resolved spectroscopic study on <b>Py-CHO</b> in an organic-water (THF:water) biphasic system, in a solid state, and in stearic acid-supported Langmuir-Blodgett (LB) films has been presented. <b>Py-CHO</b> shows a prominent AIE effect in water accompanied by a 10-fold quantum yield increment compared to organic solvent THF. The emission lifetime behavior was indicative of coexistence of excimer as well as aggregates. The aggregation nature of <b>Py-CHO</b> in aqueous solution was compared and contrasted to the same in the solid state (powder) and stearic acid-supported LB films with the aid of time-resolved emission lifetime measurements. It was observed that in aqueous solution, only H and J aggregates are formed, whereas in the solid state and LB films, mutual coexistence of monomer, excimer, and J and H aggregates was obtained. The current results are significant as they serve as a guideline to tune the optically differing aggregates in an AIEgen by changing the phase of the same from aqueous solution to powder form and in LB films, which can have multiple optoelectronic applications.