A TD-DFT Molecular Screening for Fluorescence Probe based on Excited-State Intramolecular Proton Transfer of 2’-Hydroxychalcone Derivatives

Abstract A systematic screening of fluorescence probe based on excited-state intramolecular proton transfer (ESIPT) of 2’-hydroxychalcone (2HC) derivatives with different electron donating (EDG) and electron withdrawing (EWG) groups at para position of phenol moiety (R1) and para position of the connected benzene ring to carbonyl (R2) of 2HC has been carried out by the best method of choice at ωB97XD/6-311++G(d,p) level. Seven selected 2HC derivatives with OH donor having mono-substitution with –NMe2 at R1 position or di-substitution with –NMe2 at R1 position and EDG (Me, OMe, NMe2) or EWG (Br, Cl, F) at R2 position have passed all required parameters (photophysical parameters, kinetic and thermodynamic parameters). Whereas, seven selected 2HC derivatives with NH donor having the same substituents as the 2HC derivatives with OH donor have passed photophysical parameters but failed kinetic and thermodynamic parameters due to high PT barrier and endothermic reaction. To ensure the effective ESIPT occurrence, a hydrogen atom on the amine group of NH donor derivatives is replaced with a tosyl (Ts) group, providing the Ts-substituted NH donor derivatives. The Ts substituent helps strengthening the intramolecular hydrogen bond, leading to low PT barrier with exothermic reaction thus facilitating ESIPT process. The systematically screening procedure from this theoretical calculation are beneficial for the design of fluorescent molecular probes utilizing the ESIPT process.