Exploring of indole derivatives for ESIPT emission: A new ESIPT-based fluorescence skeleton and TD-DFT calculations

ABS T R A C T Appropriate synthesis methods gave six different indole derivatives substituted at the C-2 or C-3 position. ESIPT emission capacities of these derivatives were investigated. It was concluded that the indole derivative containing the 1,2-dicarbonyl group at the C-2 position has ESIPT emission. Although adding water to the DMSO solution of the ESIPT-based molecule (9:1) resulted in ESIPT quenching, steady-state measurements in MeOH did not occur ESIPT quenching. TD-DFT calculation for uncovering the ESIPT mechanism emerged that the ESIPT mechanism occurred as a barrierless process. The X-ray analysis and DFT conformational analysis revealed that NH and CO groups involving proton transfer mechanisms are in the cis position. A mono-exponential decay was observed in DMSO and MeOH solutions, in which lifetimes were measured as 6.1 and 5.5 ns, respectively. pH studies revealed that acidic and basic solutions of molecule 7 did not influence ESIPT emission.