Study on the catalytic role of hydrogen-bond in the phtoinduoed cis【tautomer】trans isomerization of napththol

根据羟基相对于萘环的取向不同，萘酚有两种异构体形式，分别称为顺式和反式。这两种旋转异构体的存在是由伊藤及其同事利用激光光谱技术结合超音速射流首次提出的。后来，普拉特和同事通过分析喷射冷却萘酚的旋转分辨电子光谱来分配它们。从那时起，一些研究人员开始讨论激光操纵顺式【互变异构体】反式异构化的可能性。然而，到目前为止，它还没有实现。在这项研究中，我们旨在利用紫外-红外逐步激发在超音速射流中操纵顺式【互变异构体】反式异构化。首先，用可调紫外激光脉冲选择性地将一个特定的异构体激发到S_1态。红外激光脉冲进一步激发S_1中的分子或团簇产生X- h拉伸振动，其中X表示C、O或N原子。投入到X-H伸缩振动中的能量立即被IVR重新分配到其他振动模式中，其中一部分会流入到异构化坐标中。如果能量大到足以克服异构化势垒，反应就会发生，产物就会发出荧光。我们不仅研究了裸分子，还研究了氢键团簇，发现裸分子在3510 cm^<-1>的能量范围内不发生反应。另一方面，氢键团簇的反应发生在2900 cm^<-1>。如此大的还原表明，氢键起到了催化反应的作用。此外，我们发现在低红外频率下，簇中顺反异构化发生得非常有效，但由于与同一异构体内氢键解离的竞争，产率随着能量的增加而迅速下降。1-和2-萘酚氢键簇均发生异构化，它们之间的势垒高度相似。在实验的基础上，我们进行了DFT和时间相关的DFT计算，以获得异构化势垒高度，并研究了S_0、S_1和S_2态氢键的影响。虽然计算预测了S_1的势垒高度会大幅增加，但没有预测到氢键形成时势垒高度会下降。进一步的计算正在进行中。少

There are two isomeric forms in naphthol, depending on the orientation of hydroxyl group with respect to the naphthalene ring, which are called cis and trans. The existence of the two rotational isomers was first proposed by Ito and coworkers by uses of laser spectroscopic technique combined with a supersonic jet. Later, Pratt and coworkers assigned them by analyzing rotationally resolved electronic spectrum of jet cooled naphthol. Since then, the possibility of the laser manipulation of cis【tautomer】trans isomerization has been discussed by several researchers. Up to now, however, it has not been realized yet. In this research, we aimed to manipulate the cis【tautomer】trans isomerization for electronically excited by use of UV-IR stepwise excitation in a supersonic jet. First, a specific isomer was selectively excited to the S_1 state with a tunable UV laser pulse. The molecule or cluster in S_1 is further excited to its X-H stretching vibration by the IR laser pulse, where X refers to … More the C,O or N atom. The energy put in to the X-H stretching vibration is immediately redistributed into other vibrartional modes by IVR, and part of them will flow into the iromerization coordinate. If the energy is large enough to overcome the isomerization barrier, the reaction will occur and the product emits fluorescence.We investigated not only bare molecule but also the hydrogen-bonded clusters and found that the reaction does not occur for bare molecule within the examined energy region up to 3510 cm^<-1>. On the other hand, the reaction occurred at 2900 cm^<-1> for hydrogen-bonded clusters. Such a larger reduction indicates that H-bond acts as a catalyst for the reaction. Furthermore, we fond in the clusters the cis-trans isomerization occurs very efficiently at low IR frequency but the yield decrease rapidly with the energy due to the competition with the dissociation of H-bond within the same isomer. The isomerization occurred both 1- and 2-napthol H-bonded clusters and the barrier height seems to be similar between them. Parallel to the experiments, we performed DFT and time-dependent DFT calculation to obtain the isomerization barrier height and to investigate the effect of H-bond in S_0, S_1 and S_2 states. Thought the calculation predicted large increase of the barrier height in S_1, it failed the decrease of the height upon the H-bond formation. Further calcuation is in progress. Less