Department of Chemistry, Pohang University of Science and Technology, Pohang, 790-784, Korea.
J Phys Chem A. 2010 May 13;114(18):5618-29. doi: 10.1021/jp909438p.
Excited state intramolecular proton transfer (ESIPT) and subsequent intramolecular charge transfer (ICT) dynamics of a 2-(2'-hydroxyphenyl)benzoxazole derivative conjugated with an electron withdrawing group (HBOCE) in solutions and a polymer film has been investigated by femtosecond time-resolved fluorescence (TRF) and TRF spectra measurements without the conventional spectral reconstruction method. TRF with high enough resolution (<100 fs) reveals that the ESIPT dynamics of HBOCE in liquids proceeds by at least two time constants of approximately 250 fs and approximately 1.2 ps. The relative amplitude of the slower picosecond component is smaller in the polymer film than that in solution. Conformational heterogeneity in the ground state originating from the dispersion of the dihedral angle between the phenolic and benzoxazole groups is invoked to account for the dispersive ESIPT dynamics in liquids. From the TRF spectra of both the enol and keto isomers, we have identified the ICT reaction of the keto isomer occurring subsequent to the ESIPT. The ICT proceeds also by two time constants of near instantaneous and 2.7 ps. Since the ICT dynamics of HBOCE is rather close to the polar solvation dynamics, we argue that the ICT is barrierless and determined mostly by the solvent fluctuation.
激发态分子内质子转移 (ESIPT) 和随后的分子内电荷转移 (ICT) 动力学的 2-(2'-羟基苯基)苯并恶唑衍生物共轭与一个电子吸电子基团 (HBOCE) 在溶液和聚合物膜已经研究了飞秒时间分辨荧光 (TRF) 和 TRF 光谱测量而没有传统的光谱重建方法。TRF 具有足够高的分辨率 (<100 fs) 表明 ESIPT 动力学的 HBOCE 在液体中进行至少两个时间常数约 250 fs 和大约 1.2 ps。较慢的皮秒组件的相对幅度较小聚合物薄膜比在解决方案中。构象异质性在起源于酚和苯并恶唑基团之间的二面角的分散的基态被调用来解释在液体中的弥散 ESIPT 动力学。从烯醇和酮异构体的 TRF 光谱，我们已经确定了酮异构体的 ICT 反应发生在 ESIPT 之后。ICT 也通过两个时间常数的近瞬时和 2.7 ps。由于 HBOCE 的 ICT 动力学是相当接近的极性溶剂化动力学，我们认为 ICT 是无势垒的，主要由溶剂波动决定。
