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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Electronic Spectra of Two Long-Lived Photoproducts: Double-Proton Transfer in7-Hydroxyquinoline Dimer in a 2-Methyltetrahydrofuran Glass Matrix
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Electronic Spectra of Two Long-Lived Photoproducts: Double-Proton Transfer in7-Hydroxyquinoline Dimer in a 2-Methyltetrahydrofuran Glass Matrix

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摘要

Photoreactions of 7-hydroxyquinoline (7-HQ) in low-temperature (77-100 K) 2-methyltetrahydrofuran glassmatrices are investigated using electronic spectroscopy. We have observed fluorescence excitation andfluorescence spectra of two long-lived species generated by irradiation of UV light (230-400 nm). Thedominant species responsible for the fluorescence spectrum between 470 and 600 nm was assigned to theS1fS0 (ππ*) transition of the keto form of cyclic 7-HQ dimer (7-HQ)2 produced by excited-state doubleprotontransfer, the corresponding S1-S0 fluorescence excitation spectrum of which was detected between360 and 510 nm. Temperature dependence of the fluorescence excitation spectra showed the occurrence ofketo f enol isomerization in the S0 state of (7-HQ)2 due to a back double-proton transfer. A very slow ratefor the keto f enol isomerization implies that the potential barrier height for the back double-proton transferreacion is substantially high. Theoretical calculations at the MP2/aug-cc-pVDZ level of theory indicate thatthe enol and keto forms of cyclic (7-HQ)2 are nonplanar, therefore a large change in the geometry is necessaryfor the back double-proton transfer. A second long-lived species that emits between 410 and 600 nm hasbeen tentatively assigned to the D3(2A′′) f D0(1A′′) transition of the 7-quinolinoxyl radical on the basis ofcalculated electronic transition energies for possible candidates obtained by MS-CASPT2/aug-cc-pVDZ levelcalculations as well as IR study of 7-HQ in argon matrices Sekine, M.; Nagai, Y.; Sekiya, H.; Nakata, M.J. Phys. Chem. A 2009, 113, 8286. Photoreaction processes leading to the two long-lived species have beendiscussed.
机译：利用电子光谱研究了7-羟基喹啉（7-HQ）在低温（77-100 K）2-甲基四氢呋喃玻璃基质中的光反应。我们观察到紫外光照射（230-400nm）产生的两种长寿命物种的荧光激发和荧光光谱。负责 470 至 600 nm 之间荧光光谱的优势物质被分配到激发态双质子转移产生的环状 7-HQ 二聚体 [（7-HQ）2] 酮形式的 S1fS0 （ππ*） 跃迁，其相应的 S1-S0 荧光激发光谱在 360 至 510 nm 之间检测到。荧光激发光谱的温度依赖性表明，由于反向双质子转移，在（7-HQ）2的S0态下发生了酮f烯醇异构化。酮 f 烯醇异构化的速率非常慢，这意味着后双质子转移反应的潜在势垒高度非常高。MP2/aug-cc-pVDZ理论水平的理论计算表明，环状（7-HQ）2的烯醇和酮形式是非平面的，因此对于反向双质子转移，几何形状的大幅变化是必要的。根据通过MS-CASPT2/aug-cc-pVDZ能级计算以及氩基质中7-HQ的IR研究获得的可能候选物的电子跃迁能，暂定将发射波长在410至600 nm之间的第二个长寿命物种分配给7-喹啉氧基自由基的D3（2A′′）f D0（1A′′）跃迁[Sekine， M.;永井，Y.;关谷，H.;中田， M. J. Phys. Chem.A 2009， 113， 8286]。已经讨论了导致两种长寿物种的光反应过程。

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