Light-Induced Opening of the Intramolecular Hydrogen Bond of UV Absorbers of the 2-(2-Hydroxyphenyl)-1,3,5-triazine and the 2-(2-Hydroxyphenyl)benzotriazole Type

Abstract

A number of 2-(2-hydroxyphenyl)-4,6-diaryl-1,3,5-triazines (HPTs) and TIN P (2-(2-hydroxy-5-methylphenyl)benzotriazole) show phosphorescence in polar solvents at 77 K which increases in intensity with UV-irradiation time until an equilibrium value is reached (phosphorescence evolution). TIN P phosphoresces even at the very beginning of irradiation, in contrast to the HPTs, such as M-OH-P (2-(2-hydroxy-4-methoxyphenyl)-4,6-diphenyl-1,3,5-triazine), which exhibit no such initial phosphorescence provided that they were not recently exposed to UV radiation. The corresponding methoxy derivatives (MPTs) of some HPTs, where the H atom of the intramolecular hydrogen bond (IMHB) is replaced by a methyl group, produce intense phosphorescence independent of irradiation time. Considerable relaxation is found for HPTs after dark periods ≤ 1 h at 77 K resulting in a significantly lower initial phosphorescence intensity upon renewed irradiation. TIN P, in contrast, shows much slower relaxation which becomes significant only at elevated temperatures. Phosphorescence evolution is due to open conformers of the molecules, i.e., with intermolecular rather than intramolecular hydrogen bonds, which are formed in polar solvents under the influence of UV radiation. Relaxation, i.e., re-formation of the IMHB of open-form molecules, is faster for the investigated HPTs than for TIN P.

Theoretical Study of Benzotriazole UV Photostability: Ultrafast Deactivation through Coupled Proton and Electron Transfer Triggered by a Charge-Transfer State

“…[1][2][3][4][5][6][7] This is also thought to be the decay mechanism for other photostabilizers such as hydroxyphenyl triazines. 4 Such molecules contain a strong intramolecular hydrogen bond in the ground state, which is believed to be essential for the photostability of these compounds.…”

“…4 Such molecules contain a strong intramolecular hydrogen bond in the ground state, which is believed to be essential for the photostability of these compounds. [1][2][3][4][5][6] The fact that benzotriazole photodeactivation occurs on an ultrafast time scale suggests the involvement of conical intersections on the intramolecular proton-transfer reaction path. [8][9][10][11][12] Conical intersections can act as efficient decay funnels leading from the excited state to the ground state within a single vibrational period and are ubiquitous throughout ultrafast photochemistry and photophysics.…”

Role of a UV Absorber as a Matrix for Analysis of Polystyrene Using Matrix-Assisted Laser Desorption/Ionization-Mass Spectrometry

“…They absorb destructive UV radiation and dissipate the energy in the form of heat. [9][10][11][12][13][14][15] In general, the UV absorbers absorb UV wavelength between 295 and 400 nm, so they can potentially play a role as a matrix in MALDI analysis. 16,17 In this study, the UV absorbers were employed as the matrix to analyze polystyrene (PS) using MALDI-MS.…”

Analysis of Polymeric UV Absorber (Tinuvin 213) Using LDI-TOFMS: Solvent Effect in Sample Preparation

“…They absorb potentially destructive UV radiation and dissipate the energy on a subpicosecond time scale. [1][2][3][4][5][6] The UVA is used to filter off UV radiation and dissipate the energy in the form of heat. UVAs must have a wide range of chemical and physical properties to be useful in applications, which include coatings and a wide variety of polymer products.…”

“…For the benzotriazole class UVAs, the mechanism of excited-state deactivation is thought to be due to an excited-state intramolecular proton transfer (Scheme 2). [1][2][3][4][5][6][7] Analysis of polymer additives by mass spectrometry and its related techniques enhanced the capability of compound identification. Moving toward higher molecular weight additives with less volatility, conventional mass spectrometry techniques such as electron ionization (EI), chemical ionization (CI), and gas chromatography/mass spectrometry (GC/MS) are generally not suitable for their analysis.…”