Chipem Francis A S, Malakar Ashim, Krishnamoorthy Govindarajan
Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati, India.
Photochem Photobiol. 2015 Mar-Apr;91(2):298-305. doi: 10.1111/php.12411. Epub 2015 Jan 20.
The intramolecular proton transfer in a newly synthesized molecule, 2-(2'-hydroxyphenyl)oxazolo[4,5-b]pyridine (HPOP) is studied using UV-visible absorption, fluorescence emission, fluorescence excitation and time-resolved fluorescence spectroscopy. In the ground state, the molecule exists as cis- and trans-enol in all the solvents. However, in dioxane, alcohols, acetonitrile, dimethylformamide and dimethylsulfoxide the keto tautomer is also observed in the ground state. Dual fluorescence is observed in HPOP where the large Stoke shifted emission is due to emission from the excited-state intramolecular proton transfer product, whereas the other emission is the normal emission from enol form. The fluorescence (both normal and tautomer emission) of HPOP is less than those of corresponding benzoxazole and imidazopyridine derivatives. This reveals that the nonradiative decay becomes more efficient upon substitution of electronegative atom on the charge acceptor group. The pH studies substantiate the conclusion that (unlike in its imidazole analog) the third ground state species is the keto tautomer and not the monoanion. The effect of temperature on cis-enol-trans-enol-keto equilibrium and the nonradiative deactivation from the excited state are also investigated.
使用紫外可见吸收光谱、荧光发射光谱、荧光激发光谱和时间分辨荧光光谱对新合成的分子2-(2'-羟基苯基)恶唑并[4,5-b]吡啶(HPOP)中的分子内质子转移进行了研究。在基态下，该分子在所有溶剂中均以顺式和反式烯醇形式存在。然而，在二氧六环、醇类、乙腈、二甲基甲酰胺和二甲基亚砜中，基态下也观察到了酮式互变异构体。在HPOP中观察到双重荧光，其中大斯托克斯位移发射是由于激发态分子内质子转移产物的发射，而另一种发射是烯醇形式的正常发射。HPOP的荧光(正常发射和互变异构体发射)均低于相应的苯并恶唑和咪唑并吡啶衍生物。这表明，在电荷受体基团上取代电负性原子后，非辐射衰变变得更加有效。pH研究证实了以下结论：(与其咪唑类似物不同)第三种基态物种是酮式互变异构体而非单阴离子。还研究了温度对顺式烯醇-反式烯醇-酮平衡的影响以及激发态的非辐射失活。
