The keto→enol photoisomerization of N‐salicilydenemethylfurylamine: Nonadiabatic ab initio dynamics simulation

Abstract

The photoinduced isomerization of cis-keto and trans-keto isomers in N-salicilydenemethylfurylamine has been studied using the surface-hopping approach at the CASSCF level of theory. After the cis-keto or trans-keto isomer is excited to S 1 state, the molecule initially moves to a excitedstate local minimum. The torsional motion around relative bonds in the chain drives the molecule to approach a keto-form conical intersection and then nonadiabatic transition occurs. According to our full-dimensional dynamics simulations, the trans-keto and enol photoproducts are responsible for the photochromic effect of cis-keto isomer excited to S 1 state, while no enol isomer was obtained in the photoisomerization of trans keto on excitation. The cis keto to enol and cis keto to trans keto isomerizations are reversible photochemical reactions. It is confirmed that this aromatic Schiff base is a potential molecular switch. Furthermore, the torsion of CAN bond occurs in the radiationless decay of trans-keto isomer, while it is completely suppressed by an intramolecular hydrogen bonding interaction in the dynamics of cis-keto form. Moreover, the excited-state lifetime of cis keto is longer than that of trans-keto form due to the OÁÁÁHAN hydrogen bond.aromatic Schiff base, conical intersection, dynamics simulations, keto-enol photoisomerization, Zhu-Nakamura theory 1 | I N TR ODU C TI ON Photochromism is a phenomenon that occurs in the ultrafast photochemical reactions in nature, including processes such as photochemical ringclosure or ring-opening reactions, cis-trans or trans-cis isomerization, or intramolecular proton transfer. [1] The photochromism phenomena have attracted great attention for technological application as optical data processing, high-density information storage devices, logic devices, photoswitches, and light-driven molecular motors. [2][3][4][5][6][7][8][9] It is noteworthy that the photochromic and thermochromic properties of aromatic Schiff bases have been widely investigated both experimentally and theoretically. [10][11][12][13][14][15][16][17][18][19][20] It has been reported that the photochromism and thermochromism phenomena in these compounds occur due to two ultrafast processes: cis-trans or trans-cis isomerization and intramolecular proton transfer from the hydroxyl to the amino group. The ground-or excited-state intramolecular proton transfer (GSIPT or ESIPT) phenomena are of particular interest and have been studied extensively by diverse investigations. [21][22][23] During the photochemical processes of aromatic Schiff bases, the GSIPT or ESIPT behavior can result in photochromism between enol and keto tautomers. [14][15][16]19,20] N-salicilydenemethylfurylamine (SMFA) is a new salicylaldehyde Schiff base, as depicted in Figure 1. Recently, a theoretical exploration of the excited-state deactivation mechanisms of SMFA has been done with the CC2 method by Moghadam et al. [24] Excited-state reaction coordinates and potential energy profiles of the ground (S 0 ) and lowest excited singlet (S 1 ) st...

Keto‐enol tautomerism of the 4,5‐dimethyl‐2‐(2′‐hydroxyphenyl)imidazole in water solution: Modeling equilibrium between neutral forms and accurate assignment of the absorption bands

“…Spectroscopic studies distinguish presence of several absorption bands, but it is not possible to attribute each of them to the particular tautomeric forms. Such chromophores usually undergo excited-state intramolecular proton transfer [4][5][6], that is utilized in chemical sensors [7,8], lasers [9,10] and other applications.…”