New Insights on the Photochromism of 2-(2‘,4‘-Dinitrobenzyl)pyridine

Abstract

The photochromic behavior of 2-(2′,4′-dinitrobenzyl)pyridine (R-DNBP) has been followed in poly(methyl methacrylate) (PMMA) films and benzene solutions to clarify the behavior of a precursor state, previously identified in studies on crystalline R-DNBP at low temperatures. In PMMA films, photolysis at temperatures e50 K led to the concurrent formation of a NH tautomer and a colorless intermediate, which was stable for several hours. On irradiation at low temperatures and warming the sample, the colorless intermediate was seen to react to produce the NH tautomer in a higher yield than that found in the direct photolysis. Further information on this intermediate has come from flash photolysis studies in benzene solution, in which a new transient absorption has been observed at 335 nm and assigned to this species. This decays within a few microseconds at room temperature to form an OH tautomer, which then interconverts to the NH tautomer. The precursor state is not quenched by oxygen or naphthalene. From consideration of the kinetic and spectral data, it is suggested that this new species corresponds to a nonrelaxed tautomeric form of the OH state of R-DNBP.

Crystal structure of 2-(2',4' -diphenylsulfonylbenzyl)pyridine, C24H19NO4S2

“…The proton transfer process from the methylene carbon atom towards the nitrogen atom of the pyridine has been characterized for a-DNBP [4][5][6], and assumed to be assisted by the o-nitro group. To test this assumption, it was synthesized the 2-(2' ,4' -diphenylsulfonylbenzyl)-pyridine [ 1 ], a new a-DNBP derivative in which the electron withdrawing nitro groups have been replaced by sulfone groups, and shown that this derivative is photochromic in solution and in the crystal.…”

Enhancements on the Photochromism of 2-(2,4-Dinitrobenzyl)pyridine: Molecular Modeling, NMR Spectrometry, Photo- and Solvent-Bleaching

“…The final photoproduct from α-DNBP using light of λ = 370-420 nm is the NϪH quinoid tautomer (NϪH form), consistent with its IR, visible, and 2D NOESY 1 H NMR spectra (7) (Scheme I). The NϪH form arises from the short-lived aci-nitro tautomer (OϪH form), a tauto-merization that is supported by time dependent studies employing polarized reflection and absorption spectra combined with FT-IR and Raman spectral data obtained from a single crystal of irradiated α-DNBP (8) and from photolysis studies in poly(methylmethacrylate) films (9).…”

Sequential‐Stimuli Induced Stepwise‐Response of Pyridylpyrenes

“…[27] Since then, numerous pyridine-derived compounds have been explored for photo-responsive smart materials. [28,29] Recently, materials with both mechanochromic and photoresponsive properties have been reported, [30] which inspire us to further develop responding materials with integrated logic. In this paper, we successfully render sequential-stimuli induced stepwise-response by combining mechano-chromic and photoresponsive properties into single-component materials (Py-1-Py-3).…”

“…[ 27 ] Since then, numerous pyridine‐derived compounds have been explored for photo‐responsive smart materials. [ 28,29 ]…”