Hewett Daniel M, Tabor Daniel P, Fischer Joshua L, Sibert Edwin L, Zwier Timothy S
Department of Chemistry, Purdue University , West Lafayette, Indiana 47907, United States.
Department of Chemistry and Chemical Biology, Harvard University , Cambridge, Massachusetts 02138, United States.
J Phys Chem Lett. 2017 Nov 2;8(21):5296-5300. doi: 10.1021/acs.jpclett.7b02276. Epub 2017 Oct 16.
An ultraviolet-infrared (UV-IR) double-resonance method for recording conformation-specific excited-state infrared spectra is described. The method takes advantage of an increase in fluorescence signal in phenylalkanes produced by infrared excitation of the S origin levels of different conformational isomers. The shorter lifetimes of these IR-excited molecules, combined with their red-shifted emission, provides a way to discriminate the fluorescence due to the infrared-excited molecules from the S origin fluorescence, resulting in spectra with high signal-to-noise ratios. Spectra for a series of phenylalkanes and a capped phenylalanine derivative (Ac-Phe-NHMe) demonstrate the potential of the method. The excited-state spectrum in the alkyl CH stretch region of ethylbenzene is well-fit by an anharmonic model developed for the ground electronic state, which explicitly takes into account stretch-bend Fermi resonance.
本文描述了一种用于记录构象特异性激发态红外光谱的紫外-红外（UV-IR）双共振方法。该方法利用了不同构象异构体的S起始能级的红外激发在苯基烷烃中产生的荧光信号增强。这些红外激发分子的较短寿命，再加上它们红移的发射，提供了一种方法来区分红外激发分子产生的荧光与S起始荧光，从而得到具有高信噪比的光谱。一系列苯基烷烃和一种封端苯丙氨酸衍生物（Ac-Phe-NHMe）的光谱证明了该方法的潜力。乙苯在烷基CH伸缩区域的激发态光谱可以很好地用为基态电子态开发的非谐模型拟合，该模型明确考虑了伸缩-弯曲费米共振。
