Laser spectroscopic research on unconventional hydrogen bonds involving borane

1.用激光光谱技术研究了水杨酸（水杨酸和5-甲氧基水杨酸）与水或甲醇的几何结构和激发态质子位错。研究了这些簇在超音速射流中的荧光激发、分散荧光和红外（IR）光谱，包括电子基态和第一激发态。根据羟基拉伸区的红外光谱，借助量子化学计算确定了团簇的几何结构。团簇中水或甲醇部分的羟基与水杨酸部分的羧基形成一个环。水杨酸部分的分子内氢键在团簇形成时仍然保持不变。结合部分氘化研究，分析了电子激发态令人费解的红外光谱。激发态的红外光谱和分散荧光光谱表明，分子内激发态的质子位错几乎不受水或甲醇微溶剂化的影响，而自救赎态的质子位错则受到强烈的抑制。还发现在电子激发下羧基OH的酸度急剧降低。采用电子和红外光谱研究了5-甲氧基水杨酸（5-McOSA）、5-甲基水杨酸（5-MeSA）、5-氟水杨酸（5-FSA）、6-氟水杨酸（6-FSA）和水杨酸甲酯（MS）在水杨酸（SA）框架中激发态质子转移（ESIPT）的取代效应。在3mm范围内测量了电子基态（S_0）和第一激发态（S_1）的红外光谱。5-MeSA和6-FSA的电子激发/发射光谱显示了典型的ESIPT光谱特征，这些特征在SA的光谱中已经发现。另一方面，5-MeOSA和5-FSA的激发和发射光谱呈镜像关系，这被认为是ESIPT抑制的结果。尽管电子光谱之间存在如此显著的差异，但红外光谱显示，在所有取代的sa的电子激发下，酚OH拉伸振动发生了剧烈变化，即所有sa的酚OH带在3mm区域消失，表明S_1中酚O-H键的伸长幅度很大（超过0.1 Å）。这一结果表明，在电子激发作用下，所有取代的sa的分子内氢键强度都显著增强。讨论了二聚体中ESIPT的取代效应。少

1.Geometric structures and the excited-state proton-dislocation in size-selected clusters of salicylic acids (salicylic acid and 5-methoxysalicylic acid) with water or methanol were studied by using laser spectroscopic techniques. Fluorescence excitation, dispersed fluorescence, and infrared (IR) spectra of those clusters in supersonic jets were examined for both the electronic ground and first excited states. The geometric structures of the clusters were determined on the basis of the IR spectra of the OH stretch region with a help of quantum chemical calculations. The hydroxyl group of the water or methanol moiety in the clusters forms a ring involving the carboxylic group of the salicylic acid moiety. The intramolecular hydrogen bond in the salicylic acid moiety is still held upon the cluster formation. The puzzling IR spectra in the electronic excited state were analyzed in combination with a partial deuteration study. The IR spectra in the excited state and dispersed fluorescence … More spectra indicated that the intramolecular excited state proton dislocation is hardly affected by the microsolvation with water or methanol, in contrast with the strong suppression of the dislocation in the self-salvation. A drastic reduction of the acidity of the carboxylic OH upon the electronic excitation was also found.2.Substitution effects on the excited state intramolecular proton transfer (ESIPT) in the salicylic acid (SA) frame were studied by electronic and infrared spectroscopy of jet-cooled 5-methoxylsalicylic acid (5-McOSA), 5-methylsalicylic acid (5-MeSA), 5-fluorosalicylic acid (5-FSA), 6-fluorosalicylie acid (6-FSA), and methyl salicylate (MS). Infrared spectra were measured in the 3 mm region for both the electronic ground (S_0) and first excited (S_1) states. The electronic excitation/emission spectra of 5-MeSA and 6-FSA showed the typical spectral features of ESIPT, which have been found in the spectra of SA. On the other hand, 5-MeOSA and 5-FSA exhibit a mirror-image relation between their excitation and emission spectra, which has been regarded as a result of the suppression of ESIPT. Despite of such a remarkable difference among the electronic spectra, IR spectroscopy exhibits that a drastic change of the phenolic OH stretching vibration does occur upon the electronic excitation of all the substituted SAs, that is, the phenolic OH band of all the SAs disappears from the 3 mm region, indicating a large elongation of the phenolic O-H bond (over 0.1 Å) in S_1. This result represents that the intramolecular hydrogen-bond strength is remarkably enhanced upon the electronic excitation in all the substituted SAs. Substitution effects on ESIPT in dimers are also discussed. Less