Ultrafast ESIPT dynamics of 4-methyl-2,6-diformylphenol

[Display omitted] We investigate the gas-phase photodynamics associated with the S1 (nπ*), S2 (ππ*) and S3 (nπ*) states of 4-methyl-2,6-diformylphenol using trajectory-based surface hopping dynamics simulations. A rapid internal conversion would populate S1 and S3 upon initiating the trajectories on “bright” S2. This nonadiabatic population behavior would lead to intramolecular proton-transfer tautomerization via three states, where the predominant tautomerization happens via S2. An average timescale of ∼ 44 fs is estimated for the tautomerization. The triplet formation can occur via energetically feasible S1-T3 (at the Franck-Condon geometry of normal tautomer) and S1-T2 (at the S1 equilibrium minimum of proton-transferred tautomer) pathways. Intersystem crossing and the forbidden nature of S1 (nπ*) makes the molecule exhibit weak fluorescence.