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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Excited-state proton transfer through water bridges and structure of hydrogen-bonded complexes in 1H-pyrrolo[3,2-h] quinoline: Adiabatic time-dependent density functional theory study
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Excited-state proton transfer through water bridges and structure of hydrogen-bonded complexes in 1H-pyrrolo[3,2-h] quinoline: Adiabatic time-dependent density functional theory study

机译：1H-吡咯并[3,2-h]喹啉中水的激发态质子转移和氢键配合物的结构：绝热时间依赖性密度泛函理论研究

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摘要

Proton transfer reaction is studied for 1H-pyrrolo[3,2-h]quinoline-water complexes (PQ-(H2O)(n), n = 0-2) in the ground and the lowest excited singlet states at the density functional theory (DFT) level. Cyclic hydrogen-bonded complexes are considered, in which water molecules form a bridge connecting the proton donor (pyrrole NH group) and acceptor (quinoline nitrogen) atoms. To understand the effect of the structure and length of water bridges on the excited-state tautomerization in PQ, the potential energy profile of the lowest excited singlet state is calculated adiabatically by the time-dependent DFT (TDDFT) method. The S-0 -> S-1 excitation of PQ is accompanied by significant intramolecular transfer of electron density from the pyrrole ring to the quinoline fragment, so that the acidity of the N-H group and the basicity of the nitrogen atom of the quinoline moiety are increased. These excited-state acid-base changes introduce a driving force for the proton transfer reaction. The adiabatic TDDFT calculations demonstrate, however, that the phototautomerization requires a large activation energy in the isolated PQ molecule due to a high energy barrier separating the normal form and the tautomer. In the 1:1 cyclic PQ- H2O complex, the energy barrier is dramatically reduced, so that upon excitation of this complex the tautomerization can occur rapidly in one step as concerted asynchronous movements of the two protons assisted by the water molecule. In the PQ-(H2O)(2) solvate two water molecules form a cyclic bridge with sterically strained and unfavorable hydrogen bonds. As a result, some extra activation energy is needed for initiating the proton dislocation along the longer hydrogen-bond network. The full tautomerization in this complex is still possible; however, the cooperative proton transfer is found to be highly asynchronous. Large relaxation and reorganization of the hydrogen-bonded water bridge in PQ-( H2O) 2 are required during the proton translocation from the pyrrole NH group to the quinoline nitrogen; this may block the complete tautomerization in this type of solvate.
机译：在密度泛函理论下研究了1H-吡咯并[3,2-h]喹啉-水络合物（PQ-（H2O）（n），n = 0-2）和最低激发单重态的质子转移反应（DFT）级别。考虑到环状氢键结合的配合物，其中水分子形成连接质子供体（吡咯NH基）和受体（喹啉氮）原子的桥。为了了解水桥的结构和长度对PQ中激发态互变异构的影响，通过时变DFT（TDDFT）方法绝热计算了最低激发单重态的势能分布。 PQ的S-0-> S-1激发伴随着电子密度从吡咯环到喹啉片段的明显分子内转移，因此NH基团的酸度和喹啉部分的氮原子的碱性是增加。这些激发态酸碱变化引入了质子转移反应的驱动力。绝热TDDFT计算证明，由于高能垒将正常形式和互变异构体分开，光互变异构在分离的PQ分子中需要较大的活化能。在1：1环状PQ-H2O络合物中，能垒显着降低，因此在激发该络合物时，互变异构化可以一步一步快速发生，这是两个质子在水分子协助下协调一致的异步运动。在PQ-（H2O）（2）溶剂化物中，两个水分子形成具有空间应变和不利氢键的环状桥。结果，需要一些额外的活化能来引发沿较长氢键网络的质子位错。在这种复合物中完全互变异构仍然是可能的。然而，发现合作质子转移是高度异步的。在质子从吡咯NH基团转移到喹啉氮的过程中，PQ-（H2O）2中的氢键水桥需要大量弛豫和重组。这可能会阻止这类溶剂化物中的完全互变异构。

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