Sie befinden Sich nicht im Netzwerk der Universität Paderborn. Der Zugriff auf elektronische Ressourcen ist gegebenenfalls nur via VPN oder Shibboleth (DFN-AAI) möglich. mehr Informationen...
Probing the Intramolecular Hydrogen Bond of 2-(2-Hydroxyphenyl)benzotriazoles in Polar Environment: A Photophysical Study of UV Absorber Efficiency
Ist Teil von
The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory, 2007-10, Vol.111 (39), p.9733-9744
Ort / Verlag
United States: American Chemical Society
Erscheinungsjahr
2007
Quelle
Alma/SFX Local Collection
Beschreibungen/Notizen
An in-depth photophysical study is presented for a series of 2-(2-hydroxyphenyl)benzotriazoles (HBzTs); the structural characteristic of all these photostabilizers is their strong intramolecular hydrogen bridge (IMHB). Tinuvin P (TIN P, 11a) and six other HBzTs, with no substituent in the 3‘-position ortho to the hydroxy function, show pronounced phosphorescence already in the dark (at 77 K in a polar glass). Upon irradiation, the phosphorescence intensity rises further until an equilibrium value is attained (up to 1.5 fold the dark value). A kinetic model is given which excellently reproduces this phosphorescence evolution: it demonstrates phosphorescence to arise from open conformers where the IMHB has been broken. Phosphorescence excitation spectra match the absorption spectra of the open conformer and also that of the O-methyl homologue 11A which cannot form an IMHB. Fluorescence spectra likewise prove the equilibrium between the closed and open conformer for these HBzTs. In unpolar glasses as well as in the crystalline state, TIN P displays a long-wavelength (red) fluorescence (with an enormous Stokes shift of ∼10.000 cm-1) which is associated with the excited singlet state of the closed form after proton transfer within the IMHB, S1‘(C). In polar matrixes, on the other hand, a blue fluorescence is observed (with a regular Stokes shift) for all those HBzTs which have no 3‘-substituent shielding the IMHB against being opened by the polar solvent. This blue fluorescence, just as the characteristic phosphorescence evolution for these compounds, is associated with the open conformer. For HBzTs with an (alkyl) group ortho to the bridging OH group, however, a long-wavelength (red) fluorescence is again observed. The shielding effect of the 3‘-substituent shows a fine gradation, cumyl ≥ 1,1,3,3-tetramethylbutyl (isooctyl) > t-butyl ≥ methyl.
Sprache
Englisch
Identifikatoren
ISSN: 1089-5639
eISSN: 1520-5215
DOI: 10.1021/jp0721189
Titel-ID: cdi_proquest_miscellaneous_68317321
Format
–
Weiterführende Literatur
Empfehlungen zum selben Thema automatisch vorgeschlagen von bX