Revealing the Dynamic of Excited State Proton Transfer of a π‑Conjugated Salicylidene Compound: An Experimental and Theoretical Study

Excited state intramolecular proton transfer (ESIPT) in a novel salicylidene sal-3,4-benzophen chromophore is studied by white-light femtosecond pump–probe and time-resolved fluorescence techniques, as well as by theoretical calculations under the time dependent density functional theory framework. We show that when the sal-3,4-benzophen chromophore (in <i>enol</i> form) is excited (at 390 nm) to the <i>cis-enol*</i> form, it is quickly converted to the hot <i>cis-keto*</i> (hK*) form due to the fast ESIPT process (τ_ESIPT = 150 fs). Subsequently, cooling from the hot <i>cis-keto*</i> (hK*) to cold <i>cis-keto*</i> (cK*) state takes place with a characteristic time constant of ∼600 fs, with following relaxation decay time of 37 ps related with the photodynamic from sal-3,4-benzophen due to the occurrence of the <i>cis → trans</i> photoisomerization and intersystem crossing mechanisms. Finally, we observed the fluorescence emission from the <i>cis-keto*</i> at 575 nm. The dynamics of the optical process was modeled using rate equations with the proper energy level diagram and supported by theoretical calculations