Deactivation processes of ultraviolet stabilizers of the 2-(hydroxyphenyl)benzotriazole class with intramolecular hydrogen bonds

Goeller, Gernot; Rieker, Jochen; Maier, Andreas; Stezowski, John J.; Daltrozzo, Ewald; Neureiter, Manfred; Port, H.; Wiechmann, M.; Kramer, Horst E. A.

doi:10.1021/j100317a018

Cited by 56 publications

(60 citation statements)

References 8 publications

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“…1,2 ESIPT molecules have attracted particular attention from the viewpoint of developing new functional molecules such as fluorescent probes, [3][4][5][6] laser dyes, [7][8][9] and photostabilizers. [10][11][12][13][14][15][16] The ESIPT process involves a phototautomerization reaction to yield an excited keto form (K*) in the subpicosecond time region, with the molecule changing from the original enol form (E) to the keto form on photoirradiation ( Figure 1). [17][18][19][20][21][22][23][24][25][26][27] The excited keto form K* relaxes radiatively to give a large Stokesshifted fluorescence or nonradiatively to the ground-state keto form (K), which then undergoes thermal re-enolization to give the original E form.…”

Section: Introductionmentioning

confidence: 99%

Excited-State Intramolecular Proton Transfer of Naphthalene-Fused 2-(2′-Hydroxyaryl)benzazole Family

et al. 2010

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Intramolecularly hydrogen-bonded organic compounds often exhibit fluorescence emission at considerably longer wavelengths than typical fluorescence as a result of excited-state intramolecular proton transfer (ESIPT). The structure-property relationship of such ESIPT molecules, however, remains obscure. The present article reports the excited-state dynamics of a new family of ESIPT molecules, 2-(2'-hydroxynaphthyl)benzazoles 1-3, based on steady-state and time-resolved spectroscopy measurements. In comparison with the parent compound HBO, all three compounds 1-3 exhibited absorption bands at longer wavelengths and emitted fluorescence from the excited keto-tautomer K* at shorter wavelengths, indicating that the introduction of a naphthalene ring increases the energy gap between the ground and excited states for the keto-tautomer despite the expansion of the aromatic ring. Time-resolved fluorescence spectra revealed dual emission for compounds 1 and 3, consisting of two distinct fluorescence bands originating from K* and the excited rotamer E'*, whereas 2 exhibited fluorescence only from the K* state. In the transient absorption spectra, both the T-T absorption band and the ground state absorption band of the Z-keto tautomer were observed for 1, whereas only the T-T absorption band was observed for 2 and only the Z-keto tautomer band was observed for 3.

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Section: Introductionmentioning

confidence: 99%

Excited-State Intramolecular Proton Transfer of Naphthalene-Fused 2-(2′-Hydroxyaryl)benzazole Family

et al. 2010

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“…Therefore, it is very important for the design of new photostabilizers to know the factors that contribute to a fast radiationless deactivation, and many research studies were devoted to unravel the photophysics of this family of compounds by theoretical and experimental methods. [47][48][49][50][51][52][53][54][55] On the other hand, HBO and HBT were explored for nonlinear optical applications and lightemitting devices. [56][57][58] These and other ESIPT dyes were also examined for a wide range of applications, including the abovementioned UV photostabilizers, fluorescence sensors, laser dyes, data storage, optical switches, UV filters, etc.…”

Section: Introductionmentioning

confidence: 99%

Excited-State Intramolecular Proton Transfer in 2-(3‘-Hydroxy-2‘-pyridyl)benzoxazole. Evidence of Coupled Proton and Charge Transfer in the Excited State of Some o-Hydroxyarylbenzazoles

et al. 2007

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The influence of solvent, temperature, and viscosity on the phototautomerization processes of a series of o-hydroxyarylbenzazoles was studied by means of ultraviolet-visible (UV-vis) absorption spectroscopy and steady-state and time-resolved fluorescence spectroscopy. The compounds studied were 2-(2'-hydroxyphenyl)benzimidazole (HBI), 2-(2'-hydroxyphenyl)benzoxazole (HBO), 2-(2'-hydroxyphenyl)benzothiazole (HBT), 2-(3'-hydroxy-2'-pyridyl)benzimidazole (HPyBI), and the new derivative 2-(3'-hydroxy-2'-pyridyl)benzoxazole (HPyBO), this one studied in neutral and acid media. All of these compounds undergo an excited-state intramolecular proton transfer (ESIPT) from the hydroxyl group to the benzazole N3 to yield an excited tautomer in syn conformation. A temperature- and viscosity-dependent radiationless deactivation of the tautomer has been detected for all compounds except HBI and HPyBI. We show that this radiationless decay also takes place for 2-(3-methyl-1,3-benzothiazol-3-ium-2-yl)benzenolate (NMeOBT), the N-methylated analog of the tautomer, whose ground-state structure has anti conformation. In ethanol, the radiationless decay shows intrinsic activation energy for HPyBO and HBO; however, it is barrierless for HBT and NMeOBT and controlled instead by the solvent dynamics. The relative efficiency of the radiationless decay in the series of molecules studied supports the hypothesis that this transition is connected with a charge-transfer process taking place in the tautomer, its efficiency being related to the strength of the electron donor (dissociated phenol or pyridinol moiety) and electron acceptor (protonated benzazole). We propose that the charge transfer is associated with a large-amplitude conformational change of the tautomer, the process leading to a nonfluorescent charge-transfer intermediate. The previous ESIPT step generates the structure with the suitable redox pair to undergo the charge-transfer process; therefore, an excited-state intramolecular coupled proton and charge transfer takes place for these compounds.

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“…In benzotriazole species, the elements of donor (phenol) 28 and acceptor (triazole) 29 are present, and so the possibility also exists for TICT states in these species. 5 Therefore, we explored the effects of structural modification on the photophysics of various 2-arylbenzotriazoles.…”

Section: Introductionmentioning

confidence: 99%

Twisted Intramolecular Charge Transfer States in 2-Arylbenzotriazoles: Fluorescence Deactivation via Intramolecular Electron Transfer Rather Than Proton Transfer

et al. 2002

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Ultraviolet absorbers such as Tinuvin P (2-(2-hydroxy-5-methylphenyl)benzotriazole), 1, achieve their exceptional photostabilities as a result of deactivation of excited singlet states through excited state intramolecular proton transfer (ESIPT). Adding a methyl group to the 6′ position of 2-arylbenzotriazoles reveals an additional excited singlet state deactivation mechanism in this class of molecules which does not require intramolecular hydrogen bonding. Steady state fluorescence and fluorescence lifetime measurements for a series of 6′-methyl-2-arylbenzotriazoles provides compelling evidence for a twisted intramolecular charge transfer (TICT) mechanism of excited singlet state deactivation. Due to the steric requirements of the 6′-methyl group, conformations are favored in which the phenyl and triazole rings are no longer coplanar. In the case of compound 11 (2-(6-methoxy-2,3-dimethylphenyl)-2H-benzotriazole), the presence of a 2′-methoxy group enhances nonplanarity and results in large deactivation rates. Compound 12 (2-(6-methoxy-2,3-dimethylphenyl)-5-(trifluoromethyl)-2H-benzotriazole), which possesses both twist and enhanced donor/acceptor properties, undergoes the most efficient fluorescence quenching for the methoxyarylbenzotriazoles. Compounds with both a 6′-methyl and a hydroxy group on the phenyl ring exhibit diffusion controlled quenching (k q ) 2 × 10 10 M -1 s -1) by DMSO. This quenching appears to result from either partial or complete excited state proton transfer to DMSO, which enhances TICT deactivation of the singlet excited state.

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Deactivation processes of ultraviolet stabilizers of the 2-(hydroxyphenyl)benzotriazole class with intramolecular hydrogen bonds

Cited by 56 publications

References 8 publications

Excited-State Intramolecular Proton Transfer of Naphthalene-Fused 2-(2′-Hydroxyaryl)benzazole Family

Excited-State Intramolecular Proton Transfer of Naphthalene-Fused 2-(2′-Hydroxyaryl)benzazole Family

Excited-State Intramolecular Proton Transfer in 2-(3‘-Hydroxy-2‘-pyridyl)benzoxazole. Evidence of Coupled Proton and Charge Transfer in the Excited State of Some o-Hydroxyarylbenzazoles

Twisted Intramolecular Charge Transfer States in 2-Arylbenzotriazoles: Fluorescence Deactivation via Intramolecular Electron Transfer Rather Than Proton Transfer

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