Preparation, spectral characteristics and photolytic stability of anthracene-hindered amine probes: Influence of the medium

Abstract

New probes, esters of 3-(9-anthracene)propionic acid with 2,2,6,6-tetramethyl-4-hydroxypiperidine and its oxidized and protonized form, were prepared and spectrally characterized. Spectral measurements were performed in solution and in polymer matrices as polyethylene, isotactic polypropylene, polystyrene, polymethyl methacrylate and polyvinylchloride. Absorption spectra of these derivatives were shifted about 10 nm bathochromically in comparison with anthracene. The longest wavelength absorption band of the parent amine (probe III) and its derivatives exhibited the fine vibrational structure in solution and in all polymer matrices. Fluorescence spectra of the probes were red-shifted as compared to anthracene. The vibrational structure of this emission is well preserved in all media. Quantum yield of fluorescence of parent amine is slightly higher than anthracene in methanol. The range of values of quantum yield relative to anthracene of parent amine is rather large (0.3-11) in polymer matrices. The lifetime of fluorescence of parent amine is 3.8 ns in methanol and 4.1 ns in cyclohexane but it is larger in polymer matrices. Both quantum yield and lifetime of oxidized form were smaller in comparison with parent amine. The quantities ΦNH/ΦNO and τNH/τNO expressing the extent of intramolecular quenching (electronic energy transfer) are low for this type of probes in methanol solution. In all polymer matrices these values are higher (2-7.5) but there are some differences between ratio calculated from quantum yields and from lifetimes. The photolytical stability of the novel probes is low in polymer matrices at 366 nm irradiation. 2,2,6,6-Tetramethylpiperidine structural unit as parent amine or as stable nitroxyl radical does not exhibit any stabilization effect. © 2002 Elsevier Science B.V. All rights reserved.