2- benzimidazole, excited

Measurement of the influence of different micellar environments on proton transfer from excited states of 3-hydroxyflavone allows estimates to be made of micelle concentrations from measurement of the tautomer emission yield. Proton transfer reactions of benzimidazole excited singlet states have also been studied in ionic micelles. Magnetic fields are found to affect the behaviour of radicals generated by the photodissociation of benzil in micellar media. The starburst dendrites which are formed by anionic macromolecules in interaction with both anionic and cationic surfactants have been examined by pyrene fluorescence. Benzo[k]fluoranthrene fluorescence has served as a probe of the effects of metal salts on bile salt aggregation. The incorporation and distribution of benzoquinone into liposomes containing amphilic Zn(II) porphyrin has been followed by its effect on the quenching of the excited state °. A comparison of the photochromism of spirobenzpyran derivatives in unilamellar surfactant vesicles and solvent cast surfactant films has also been reported. ... 

The photolysis of 1,2-benzisoxazole in the absence of air in acetonitrile gave salicylonitrile and benzoxazole (67AHC(8)277). When air-saturated acetonitrile was employed, 2,2 -dimeriz-ation to (38) occurred, accompanied by benzoxazole. Photolysis of the 2,2 -dimer (38) and benzoxazole did not alter the ratio, thus indicating that neither one arose from the other. Selective excitation also ruled out dimer formation from benzoxazole under the reaction conditions (Scheme 9). This dimerization is similar to that observed for benzimidazole, except that in that series no 2,2 -dimerization was observed (74TL375). 

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]. 

Rodrigues Prieto, F., Rios Rodriguez, M. C., Mosquera Gonzalez, M. and Rios Fernandez, M. A. Ground- and excited-state tautomerism in 2-(3 -Hydroxy-2 -pyridyl)benzimidazole, J. Phys. Chem., 98 (1994), 8666-8672... 

The effects of a-, (3-, y-, and 2,6-di-o-methyl-(3-CDs on the ground- and excited-state properties of 2-(2 -hydroxyphenyl)benzoxazole (HBO), 2-(2 -hydrox-yphenyl)benzothiazole (HBT), and 2-(2 -hydroxyphenyl)benzimidazole (HBI) (42) in aqueous media have been investigated using fluorescence [184], The molecules form 1 1 complexes with a reasonably high association constant, and they enter the cavity axially from the wider-rim side of (3-CD with the benzazole... 

Unsubstituted 5(6)-nitrobenzimidazole has two absorption bands in the field of 230-235 and 300-309 nm [1186, 1190-1192], Its long-wave band, as compared with the initial benzimidazole, is bathochromically moved by approximately 25 nm and does not show vibrational structure. The short-wave band, on the contrary, undergoes a hypsochromic shift (—10 nm) upon mononitration [709, 1193], Band displacement of this kind and the disappearance of vibrational observed for the long-wave band are responsible for essential differences in the localization and, hence, in the nature of, at least, one of the transitions. For example, from CNDO/S calculations it follows that the long-wave transition of benzimidazole is multicon-figurational (Table 3.70) and results in the total molecular excitement [1193],... 

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>. 

Rotational isomerization has been described for the phototautomer formed by proton transfer in the excited singlet state of 2,2 -bipyridin-3-ol in hydrocarbon solvents. At room temperature both the primary phototautomer and its rotamer fluoresce, allowing the activation energy for internal rotation to be determined. Excited state tautomerization has also been described for camp-tothecin in acidic aqueous solution and for derivatives of hypericin. Light-induced keto-enol tautomerism has been invoked to explain the fluorescence behaviour of certain benzimidazole compounds. Interconversion of confor-mers of constrained tryptophan derivatives takes place in the first-excited singlet state.The excited state behaviour has been reported for conformationally-distorted porphyrin derivatives. The lifetimes of the S] states of these... 

Group 11. Paramagnetic (1H, 15N) NMR spectra were used to study a Cu -IDA (=iminodiacetic acid) complex localised on a protein surface. H and 13C NMR spectra were reported for copper(II) bis-benzimidazole complexes.1225 Variable temperature H NMR spectra of copper complexes of p-octafluorinated triarylcorroles reveal a thermally-accessible paramagnetic excited state, i.e. a Cu11 corrole 7i-cation radical.1226 Copper(II) forms of stellacyanin from Rhus vernicifera were characterised by H NMR.1227... 

The tautomerism of 2-(3,-hydroxy-2,-pyridyl)benzimidazole 215 in the ground and first excited singlet states in various solvents has been investigated by UV-vis absorption spectroscopy, by steady-state and time-resolved fluorescence spectroscopy, and by semiempirical AMI and ab initio RHF calculations. In the ground state, the tautomeric equilibrium 215a 215b was observed, the equilibrium shifting toward... 

Shimizu et al report that while [2.2] paracyclophane (55) undergoes two-photon dissociation in low temperature matrices by way of the triplet state, in the gas phase, the efficient two-photon process proceeds via a hot molecule formed by internal conversion from the initially formed singlet excited state. The photocleavage of 2-nitrobenzyl ethers and ester has been widely reported and has now been evaluated as a deprotection methodology for indoles, benzimidazole, and 6-chlorouracil (Voelker et al). The mechanism of the cleavage of such compounds is considered to involve the o-quinonoid intermediate, but previously these had only been deduced from transient electronic spectra produced in flash photolysis experiments. Infrared spectral data from photochemical studies of 2-nitrobenzyl methyl ether in argon and nitrogen matrices have now been published which confirm that the intermediate does indeed have the o-quinonoid structure... 

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