Ultrafast excited state intramolecular proton transfer (ESIPT) mechanism for 2,6-bis(benzothiazolyl-2-yl)phenol: A theoretical investigation

We theoretically probe into photo-induced hydrogen bonding effects between S0 and S1 states as well as excited state intramolecular proton transfer (ESIPT) behavior for 2,6-bis(benzothiazolyl-2-yl)phenol (DBTP) system. By analyzing primary geometrical parameters involved in hydrogen bond, we confirm O36-H37 center dot center dot center dot N35 of DBTP should be strengthened in the first excited state. By constructing potential energy surfaces for DBTP along with ESITP reactional orientation, we affirm that DBTP molecule undergoes the ultrafast ESIPT process. Once excited to the S1 state, DBTP quickly transfers its proton forming DBTP-PT tautomer. That is why no fluorescence of DBTP could be reported in experiment.