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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Photoinduced Proton Transfer Promoted by Peripheral Subunits for Some Hantzsch Esters
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Photoinduced Proton Transfer Promoted by Peripheral Subunits for Some Hantzsch Esters

机译：某些汉茨酯的外围亚基促进的光诱导质子转移

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摘要

It is noted that, for a small series of 3,5-diacetyl-1,4-dihydrolutidine (DDL) derivatives and the corresponding Hantzsch esters, the presence of methyl groups at the 2,6-positions serves to extinguish fluorescence in solution but not in the solid state. Emission is weakly activated and affected by changes in solvent polarity. The latter situation arises because the optical transition involves intramolecular charge transfer. Calculations, both semiempirical and DFT, indicate that, in all cases, rotation of the carbonyl function is facile and that the dihydropyridine ring is planar. These calculations also indicate that the 2,6-methyl groups do not affect the generic structure of the molecule. It is proposed that illumination increases the molecular dipole moment and pushes electron density toward the carbonyl oxygen atom. Proton transfer can now occur from one of the methyl groups, leading to formation of a relatively low-energy, neutral intermediate, followed by a second proton transfer step that forms the enol. Reaction profiles computed for the ground-state species indicate that this route is highly favored relative to hydrogen transfer from the 4-position. The barriers for light-induced proton transfer are greatly reduced relative to the ground-state process but such large-scale structural transformations are hindered in the solid state. A rigid analogue that cannot form an enol is highly emissive in solution, supporting the conclusion that proton transfer is in competition to fluorescence in solution.
机译：值得注意的是，对于少量的3,5-二乙酰基-1,4-二氢二甲基吡啶（DDL）衍生物和相应的Hantzsch酯，在2,6-位上存在甲基用于消除溶液中的荧光，但不是固态。发射微弱地激活，并受溶剂极性变化的影响。由于光学跃迁涉及分子内电荷转移，因此出现后一种情况。半经验和DFT的计算表明，在所有情况下，羰基官能团的旋转都很容易，并且二氢吡啶环是平面的。这些计算还表明2，6-甲基基团不影响分子的通用结构。提出照明可以增加分子偶极矩并将电子密度推向羰基氧原子。现在可以从一个甲基发生质子转移，导致形成相对低能量的中性中间体，然后进行第二个形成烯醇的质子转移步骤。计算的基态物质的反应曲线表明，相对于氢从4位转移而言，该路线非常受青睐。相对于基态过程，光诱导质子转移的壁垒大大降低，但这种大规模的结构转变在固态中受到阻碍。不能形成烯醇的刚性类似物在溶液中具有高发射率，支持以下结论：质子转移与溶液中的荧光竞争。

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