Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.
J Phys Chem A. 2011 Aug 11;115(31):8630-7. doi: 10.1021/jp204416m. Epub 2011 Jul 15.
Heterodyne-detected transient grating (TG) and two-dimensional photon echo (2DPE) spectroscopies are extended to the mid-UV spectral range in this investigation of photoinduced relaxation processes of adenine in aqueous solution. These experiments are the first to combine a new method for generating 25 fs laser pulses (at 263 nm) with the passive phase stability afforded by diffractive optics-based interferometry. We establish a set of conditions (e.g., laser power density, solute concentration) appropriate for the study of dynamics involving the neutral solute. Undesired solute photoionization is shown to take hold at higher peak powers of the laser pulses. Signatures of internal conversion and vibrational cooling dynamics are examined using TG measurements with signal-to-noise ratios as high as 350 at short delay times. In addition, 2DPE line shapes reveal correlations between excitation and emission frequencies in adenine, which reflect electronic and nuclear relaxation processes associated with particular tautomers. Overall, this study demonstrates the feasibility of techniques that will hold many advantages for the study of biomolecules whose lowest-energy electronic resonances are found in the mid-UV (e.g., DNA bases, amino acids).
在这项关于腺嘌呤在水溶液中光诱导松弛过程的研究中，将外差探测瞬态光栅 (TG) 和二维光子回波 (2DPE) 光谱学扩展到中紫外光谱范围。这些实验首次将一种新的产生 25 fs 激光脉冲的方法（在 263nm 处）与基于衍射光学的干涉测量提供的被动相位稳定性结合在一起。我们确定了一组条件（例如，激光功率密度、溶质浓度），适用于研究涉及中性溶质的动力学。结果表明，在激光脉冲的峰值功率较高时，会发生不需要的溶质光电离。通过 TG 测量检查了内部转换和振动冷却动力学的特征，信噪比高达 350，在短延迟时间内。此外，2DPE 线形状揭示了腺嘌呤中激发和发射频率之间的相关性，这反映了与特定互变异构体相关的电子和核弛豫过程。总的来说，这项研究证明了这些技术的可行性，这些技术将在研究中具有许多优势，因为其最低能量的电子共振处于中紫外区（例如，DNA 碱基、氨基酸）。
