Deactivation processes of 2‐hydroxyphenyl‐1,3,5‐triazines — polymeric and monomeric UV absorbers of the benzotriazole and triazine class

Keck, Juergen; Stüber, Guido J.; Kramer, Horst E. A.

doi:10.1002/apmc.1997.052520109

Cited by 14 publications

(10 citation statements)

References 52 publications

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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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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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“…Bigger et al as well as Stueber et al − have presented photophysical studies on several 2-(2-hydroxyaryl)-1,3,5-triazines and discussed how various functional groups influence the quantum yield for the proton-transferred fluorescence. Keck et al , have investigated both monomeric and polymeric UV absorbers of the benzotriazole and the triazine class with either one or two intramolecular hydrogen bridges. They have determined activation energies of 4−5 kJ mol -1 for the radiationless deactivation process from the temperature dependence of the proton-transferred fluorescence.…”

Section: Introductionmentioning

confidence: 99%

“…The radiationless deactivation process thence is concluded to originate from the proton-transferred level S 1 ‘. , Barbara et al ,, have suggested a slow, large-amplitude torsional motion for the temperature-dependent radiationless deactivation of the S 1 ‘ fluorescence of, for example, 2-(2-hydroxy-5-methylphenyl)benzotriazole (Tinuvin P (TIN P), trade name of Ciba Specialty Chemicals, Inc., see Chart 1). Elsaesser and co-workers 37 have concluded from their femtosecond experiments that the highly anharmonic in-plane deformation mode at 470 cm -1 modulates the separation between proton donor and acceptor atom, and thus plays a key role in the proton-transfer reaction of TIN P. Several comprehensive reviews deal with proton transfer in the excited state. ,,, Catalán et al recently reported results for (2-hydroxyphenyl)pyrazoles; 22a, the authors question whether proton transfer in the excited state is a prerequisite for efficient radiationless deactivation and thus for the suitability of a given compound as UV absorber 22a…”

Section: Introductionmentioning

confidence: 99%

Ultraviolet Absorbers of the 2-(2-Hydroxyaryl)-1,3,5-triazine Class and Their Methoxy Derivatives: Fluorescence Spectroscopy and X-ray Structure Analysis

et al. 1998

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A close to planar conformation is established for 2-(4-methoxyphenyl)-4,6-diphenyl-1,3,5-triazine (M-H-P) by crystal structure determination. For 2-(4-hexoxy-2-methoxyphenyl)-4,6-diphenyl-1,3,5-triazine (H-MeO-P), hydrophobic interaction between the long hexoxy groups enforces rotation of the dialkoxyphenyl ring at C6 and the C2 phenyl ring relative to the plane of the triazine ring. Time-resolved fluorescence measurements demonstrate the existence of a short-lived Franck-Condon (FC) and a longer-lived TICT (twisted intramolecular charge transfer) state, emitting at longer wavelengths, for the O-methyl derivative 2-(4-hexoxy-2-methoxyphenyl)-4,6-bis(2,4,6-trimethylphenyl)-1,3,5-triazine (H-MeO-Ms). The decay of the protontransferred (PT) fluorescence for crystalline powders of 2-(2-hydroxyphenyl)-4-(dimethylamino)-6-aryl-1,3,5triazines is shown, by the same method, to be retarded within the series phenyl f tolyl f xylyl, well in line with the gradation of quantum yields determined by steady-state methods. The high quantum yields of the PT fluorescence for triazines with only one 2-hydroxyaryl moiety on the triazine ring are reduced by 2 orders of magnitude each upon introduction of a second and a third aryl group. Most of the 2-hydroxyaryl-1,3,5triazines with additional aryl moieties at C4 and C6 show PT fluorescence, as long as the 2-hydroxyaryl and the triazine ring are more or less coplanar and the intramolecular hydrogen bond remains intact. In some cases, however, this fluorescence is very weak, or can be detected only in copolymers, in mixtures of the stabilizer with the polymer or in crystalline powders.

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“…However, Tinuvin® 1577, which lacks the methyl groups, has a nearly undetectable rate of loss in a PMMA matrix. The alkyl groups are reported to increase the lifetime of the first excited state [20,21] which leads to faster degradation. Tinuvin® 1577 appears to be the most stable commercially available UVA.…”

Section: Factors Affecting Uva Degradation Ratesmentioning

confidence: 99%

Permanence of UV Absorbers in Plastics and Coatings

Pickett¹

2001

ACS Symposium Series

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Ultraviolet absorbers (UVA's) undergo photo-degradation with quantum yields on the order of 10 -6 even in glassy, unreactive matrices such as poly(methyl methacrylate) (PMMA). The kinetics of UVA loss in a film or coating can be described by the equation: A = log 10 [(1-T 0 )10 (A0-kt) + 1] where A is the absorbance at time t, T 0 is the initial transmission, A 0 is the initial absorbance, and k is a zero order rate constant. The rate constant can be found as the slope of log 10 (10 A -1) plotted vs. exposure. The derivation and implications of these equations and a general review of UVA degradation chemistry are discussed, including the effects of the matrix material, concentration, and hindered amine light stabilizers. The rate of UV absorber loss is of relatively minor consequence when the absorber is used as a bulk additive in a polymer, but is of critical importance in the service lifetime of coatings. The kinetics of photochemical UV absorber loss and use of loss rates in coating lifetime predictions are discussed in detail.

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Deactivation processes of 2‐hydroxyphenyl‐1,3,5‐triazines — polymeric and monomeric UV absorbers of the benzotriazole and triazine class

Cited by 14 publications

References 52 publications

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

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

Ultraviolet Absorbers of the 2-(2-Hydroxyaryl)-1,3,5-triazine Class and Their Methoxy Derivatives: Fluorescence Spectroscopy and X-ray Structure Analysis

Permanence of UV Absorbers in Plastics and Coatings

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