Proton transfer 2- benzothiazole

As in the case of benzothiazoles and benzimidazoles, the excited-state proton transfer in 2-(2 -hydroxyphenyl)benzoxazole was studied both experimentally and computationally. The results closely resemble the observations for the other species The cw-enol form is preferred in the Sq ground state and the cw-keto form in the 5i excited state. Moreover, the proton transfer appears to be due to vibrational relaxation rather than thermal activation, suggesting that the aromatic ring has an impact on the transfer reaction of these systems [95JPC12456, 99JST255]. 

Chou PT, Martinez ML, Studer SL (1992) The role of the cw-keto triplet state in the proton transfer cycle of 2-(2 -hydroxyphenyl)benzothiazole. Chem Phys Lett 195 586-590... 

Brewer WE, Martinez ML, Chou PT (1990) Mechanism of the ground-state reverse proton transfer of 2-(2-hydroxyphenyl)benzothiazole. J Phys Chem 94 1915-1918... 

Cheng YM, Pu SC, Hsu CJ et al (2006) Femtosecond dynamics on 2-(2 -hydroxy-4 -diethylaminophenyl)benzothiazole solvent polarity in the excited-state proton transfer. ChemPhysChem 7 1372-1381... 

Rate coefficients in the expected range have been observed in excited state intramolecular proton transfers involving 2-(2-hydroxyphenyl)benzothiazole (Barbara et al., 1980a) and salicylideneaniline (Barbara et al., 1980b). In the former, the observation of fluorescence was explained by Scheme 2 and the... 

Qian Y, Li S, Zhang G, Wang Q, Wang S, Xu H, Li C, Li Y, Yang G (2007) Aggregation-induced emission enhancement of 2-(2 -hydroxyphenyl)benzothiazole-based excited-state intramolecular proton-transfer compounds. J Phys Chem B 111 5861-5868... 

F. Laermer, T. Elsaeser, and W. Kaiser, Femtosecond spectroscopy of excited-state proton-transfer in 2-(2 -hydroxyphenyl)benzothiazole, Chem, Phys. Lett. 148, 119(1988). 

Time-resolved electron paramagnetic resonance served to detected the short-lived triplet state of the keto tautomer (238) of 2-(2-hydroxyphenyl)benzothiazole (239) generated by excited state intramolecular proton transfer (92CC641). 

RISC has been observed by two-color irradiation for a series of photo-tautomers generated by photoinduced proton transfer [40-46]. [The parent molecules, 3-hydroxyflavone (63), 2, 3, 4, 5, 6 -pentamethylphenyl-3-hydroxyflavone (64), 7-hydroxy indanone (65), 2-(2 -hydroxyphenyl)benzothiazole (66), and 2,2 -bipyridine-3,3 -diol (67), are shown in Chart 3.] Following proton transfer in the... 

Several molecules which can undergo intramolecular proton transfer in the excited state have been found to be unusually photostable. Thus, for example, 2-hydroxybenzophenone is used as a photostabilizer in polymers while benzophenone itself is photoactive (Kysel, 1969). In crystalline 2-(2 -hydroxyphenyl)benzothiazole and its derivatives [3] a proton is transferred in the excited state from an... 

Semi-empirical AMI-SCI calculations have been performed to rationalize the photophysical behavior of two series of compounds one comprising of 2-(2 -hydroxyphenyl)benzoxazole, 2-(2 -hydroxyphenyl)benzimidazole (HBI), and 2-(2 -hydroxyphenyl)benzothiazole, and the other of 2-(2 -hydroxyphenyl)oxazole (HPO), 2-(2 -hydroxyphenyl)imi-dazole (HPI), and 2-(2 -hydroxyphenyl)thiazole (HPT). These compounds exhibit intramolecular rotation as well as excited state intramolecular proton transfer (ESIPT). The results suggested that for the first series of compounds two rotational isomers are present in the ground state of HBO and HBI while HBT has a single conformer under similar circumstances. For the other series, existence of rotamers depends very much on the polarity of the environment <2003IMS335, 2002JST(604)87>. 

AMI semi-empirical MO calculations in both gaseous and condensed phases were employed to study excited-state intramolecular proton transfer from 2-(2 -hydroxyphenyl) benzothiazole <2000CPL(327)23, 2000PCP203>. 

The dependence of intramolecular proton transfer on solvent friction has been established for 2-(2 -hydroxy-5-methylphenyl) benzotriazole in alcohol and other solvents. Excited-state proton transfer in 2-(2 -hydroxyphenyl) benzothiazole has also been studied 2 Photophysical properties and laser performance of w, w -bis ( oxazol-2-yl)- -oligophenylenes in dioxane have been measured at room temperature. +p increases with the number of phenyl rings between terminally positioned oxazoyl groups. 

Kinetics of an intramolecular proton-transfer cycle of 2-(2 -hydro-xyphenyl)benzothiazole (HBT) was investigated by the degenerative four wave mixing [47] (Scheme 2). After a preexcitation of the enol form to the... 

Light-induced intramolecular proton transfer has long been suspected to play an important role in the mechanism for photochromism in both crystals and solutions. One class of compounds that has been extensively studied is the A -salicylidene anilines. The main evidence for invoking an excited-state proton-transfer step in the photochromic mechanism comes from the observation that the colored species exists as the keto amine tautomer (in the ground state) while the bleached form exists as an enol imine (in the ground state). Replacement of the labile hydrogen with a methyl group prevents the photochemical reaction that leads to the colored species. Picosecond transient spectroscopy was used to study iV-salycylidene-o-toluidine (NST) and the related compound 2-(o-hydroxyphenyl)benzothiazole (HBT). ... 

Molecular materials, such as 2-(2-hydroxyphenyl)benzoxazole and 2-(2-hydroxyphenyl)-benzothiazole, which contain intramolecular hydrogen bonds are known to undergo excited state (charge transfer) intramolecular proton transfer upon photo-excitation. 

Jenckhe at al., explored the effects of molecular size, extent of conjugation, concentration quenching, and competition with excimer formation on intramolecular proton transfer as well as on the electro-luminescent device potential of polymeric materials. Materials like 2-(2-hydroxyphenyl)-benzoxazole and 2-(2-hydroxyphenyl)benzothiazole contain intramolecular hydrogen bonds and are known to undergo excited state charge transfer reactions and intramolecular proton transfer upon excitation. They reported, however, that the results of their studies with model compounds and several polymers, whose structure ... 

Lochbrunner S, Wurzer AJ, Riedle E (2003) Microscopic mechanism of ultrafast excited-state intramolecular proton transfer a 30-fs study of 2-(2 -hydroxyphenyl)benzothiazole. J Phys Chem A 107 10580... 

Da Silva et performed a joint experimental and theoretical work giving support to a bioluminescence mechanism in which the reactive benzothiazole hydroryl group of the firefly dioxetanone (reactant) is not deprotonated prior to the reaction. Instead, the deprotonation is suggested to take place through and excited-state proton transfer with the... 

The vast majority of papers devoted to tautomerization dynamics deal with ESIPT reactions. Since Weller s suggestion that the large Stokes shift he measured for salicyhc acid fluorescence was caused by rapid proton transfer in the excited state [62], and the development of techniques to study this on a femtosecond timescale, the field has blossomed. Most of the 2000 papers on tautomerization dynamics is on ESIPT, from both an experimental and a theoretical point of view. The number of compounds exhibiting ESIPT is far too large to discuss here. It ranges from molecules as simple as malonaldehyde to systems as complicated as 3-hydroxyflavone or 2-(2 -hydroxyphenyl)benzothiazole. In particular, substituted salicylic acids and ortho-hydroxybenzaldehydes have attracted much attention from both experimentalists and theoreticians. Weller s idea is depicted in Figure 1.10. 

Frey W, Laermer F, Elsaesser T (1991) Femtosecond studies of excited-state proton and deuterium transfer in benzothiazole compounds. J Phys Chem 95 10391-10395... 

The additional double bond in the corresponding allenyl 2-nitrophenyl sulphides causes a significant preference of the oxygen transfer to carbon88. The dominant ions correspond to the radical cations of 2[3//]-benzothiazolone and protonated benzothiazole, respectively88. Both ions require the transfer of two oxygens to carbon in the side-chain as well as extensive rearrangements of the molecules see Scheme 22. The transfer of... 

Raubenheimer et al. have developed a third route for transition metal NHC complexes with thiazol-2-ylidene, benzothiazol-2-yUdene and even isothiazol-5-ylidene ligands [45 9]. This method uses a thiazolyl transfer from lithium to a transition metal with subsequent protonation [47,49-54] or alkylation [41,45,46,48,51-56] of the nitrogen atom to generate the transition metal NHC complex. In this way, carbene complexes of copper(I)... 

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