Photophysics of a Schiff base: theoretical exploration of the excited-state deactivation mechanisms of N-salicilydenemethylfurylamine (SMFA)

Abstract

Excited state reaction coordinates and the consequent energy profiles of a new Schiff base, N-salicilydenemethylfurylamine (SMFA), have been investigated with the CC2 method, which is a simplified version of singles-and-doubles coupled cluster theory. The potential energy profiles of the ground and the lowest excited singlet state are calculated. In contrast to the ground state, the excited state potential energy profile shows a barrier-less dissociation pattern along the O-H stretching coordinate which verifies the proton transfer reaction at the S1 (ππ*) state. The calculations indicate two S1/S0 conical intersections (CIs) which provide non-adiabatic gates for radiation-less decay to the ground state. At the CIs, two barrier-free reaction coordinates direct the excited system to the ground state of enol-type minimum. According to calculation results, a trans-keto type structure obtained from photoexcitation of the enol, can be responsible for the photochromoic effect of SMFA. Furthermore, our results confirm the suggestion that aromatic Schiff bases are potential candidates for optically driven molecular switches.

Fabrication of a Hydrazone-Based Al(III)-Selective “Turn-On” Fluorescent Chemosensor and Ensuing Potential Recognition of Picric Acid

“…These bands from 320 to 460 nm indicate internal charge transfer between the imine and hydroxyl group s . 10 On addition of Al(III) (inset, Figure 1) to NDHIPH , the absorption band at 269 nm showed a slight increase in intensity, whereas the band at 383 nm showed a bathochromic shift to 391 nm (ε = 7.54 × 10 4 M –1 cm –1 ) along with the formation of two new bands at λ max of 411 nm (ε = 8.00 × 10 4 M –1 cm –1 ) and 436 nm (ε = 5.69 × 10 4 M –1 cm –1 ). The color change from colorless to bright yellow (inset, Figure 1) corroborates these shifts in absorption bands.…”

“…It exhibits a very weak fluorescence (Φ = 0.11) at λ em of 529 nm (excitation at 383 nm), which may be due to the excited-state intramolecular proton transfer (ESIPT) phenomenon, well known in the case of Schiff’s bases. 10…”

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

“…Several equilibrium geometries were obtained in ground‐state optimization due to different orientations of the methyl‐furyl part with respect to the salicylaldimine group and different orientations of the hydroxyl group . Here, optimized geometries of the most stable enol ( S 0‐ cis ‐enol), cis ‐keto ( S 0‐ cis ‐keto), and trans ‐keto ( S 0‐ trans ‐keto) isomers are presented in Supporting Information (Figure S2).…”

“…N ‐salicilydenemethylfurylamine (SMFA) is a new salicylaldehyde Schiff base, as depicted in Figure . Recently, a theoretical exploration of the excited‐state deactivation mechanisms of SMFA has been done with the CC2 method by Moghadam et al Excited‐state reaction coordinates and potential energy profiles of the ground ( S 0 ) and lowest excited singlet ( S 1 ) states were investigated. It was found that the strongly absorbent of UV radiation induces proton transfer from the hydroxyl group to the imine group in SMFA.…”

“…Previous static quantum chemical calculations and dynamics simulations have provided the detailed mechanisms of photoinduced enol→keto processes in SMFA. For aromatic Schiff bases, such as SMFA, salicylideneaniline, salicylidene methylamine, fewer studies were done to investigate the photochemical behavior in keto→enol isomerization. According to our previous studies, the simulations of enol isomer in SMFA generate three species in the S 0 state: the enol, cis ‐keto, and trans ‐keto forms .…”