Tailoring the Schiff Base Photoswitching -non- adiabatic molecular dynamics study of substituent ef- fect on Excited State Proton Transfer †

Abstract : Small molecular systems exhibiting Excited State Intramolecular Proton Transfer (ESIPT) attract considerable attention due to their possible role as ultrafast, efficient, and photostable molecular photoswitches. Here by means of static potential energy profiles scan and on-the-fly non-adiabatic dynamics simulations we study photodeactivation process of minimal-chromophore aromatic Schiff base, salicylidene methylamine (SMA), and its two derivatives 6-cyano-salicylidene methylamine (6-CN-SMA) and 3-hydroxy-salicylidene methylamine (3-OH-SMA). We show that the dominant character of the lowest excited singlet state-ππ * vs. nπ *-plays a crucial role for the system's photophysics and controls the ESIPT efficiency. We also show that the relative alignment of the ππ * and nπ * states may be controlled through chemical substitutions made to the aromatic ring of the Schiff-base molecule. We believe that our findings will improve the rational-design strategies employed for the ESIPT systems, especially in the context of their possible photoswitching.