On the photophysics of 3,5,6-Trichlorosalicylic acid: spectroscopic study combined with Hartree-Fock and Density Functional Theory calculations.

The present contribution reports a detailed photophysical study of a simple salicylic acid derivative viz., 3,5,6-Trichlorosalicylic acid (TCSA) based on steady state absorption, emission and time-resolved emission spectroscopy. Anomalous "dual" emission coupled with a large Stokes shift and negligible solvent polarity dependence marks the spectroscopic signature for Excited State Intramolecular Proton Transfer (ESIPT) reaction. Variation of medium polarity and pH of the medium have been implemented as fruitful tools to decipher the photophysics of TCSA. Quantum chemical calculation by ab initio Hartree-Fock and Density Functional Theory methods yields consistent results to follow experimental findings with distinct illustration of the inoperativeness of GSIPT reaction as well as occurrence of ESIPT process. A rigorous comparison of our experimental and theoretical measurements of TCSA with the parent compound salicylic acid, 5-chlorosalicylic acid and 3,5-dichlorosalicylic acid reveals the impact of chlorine substitution on the photophysics of the studied molecular systems with simultaneous exploration of the complexities induced in TCSA with respect to salicylic acid.