Bedeutung der Werkzeugtemperatur in der Warmumformung

Schröder, G.

doi:10.1007/978-3-642-82187-5_1

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“…It has been established for the HBzTs that the triplet state can be populated when the IMHB is disrupted by polar solvents or matrixes. ,− Turro and co-workers have found from transient absorption spectra that TIN P phenolate ions are formed in DMSO . Although the HPTs have a significantly stronger IMHB than the HBzTs ,,− and should, therefore, be insensitive to polar matrixes, they surprisingly show phosphorescence in polar solvents at 77 K indicative of triplet-state population. ,, This paper aims at giving an interpretation of this phosphorescence emission and resolving the apparent contradiction between triplet-state population and the particularly good UV-stabilizing properties of the HPTs. TIN P and its methoxy derivative (MT) as well as the methoxy derivatives (MPTs) of some HPTs are included in this study for comparison.…”

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confidence: 94%

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

et al. 2000

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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.

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