University of East Anglia - Equipment Account

超快激光技术已经发展到了这样的程度，几年前还无法想象的复杂实验现在属于可能的领域，并有可能成为例行公事。现代固体激光光源产生的超稳定脉冲宽度只有几百万亿分之一秒，在大多数电磁频谱上都具有极高的稳定性。这使几乎所有的原子或分子过程都可以进行实时讯问。在这项建议中，我们描述了三个在先进激光光谱学前沿的实验。我们的目标是发展和应用这些实验来解决分子和生物分子科学中的重要问题，以证明它们在材料表征中的实用性，并将它们确立为材料表征的重要新工具。为此，我们与世界领先的分子和生物分子材料科学实验室建立了合作关系，这些实验室将成为新方法的第一批用户。第一个实验，2D电子光谱(ES)，是研究(生物)分子组装中电子耦合和能量传输的独特工具。这些过程对太阳能的收集和利用以及光激活纳米材料的运行至关重要。在三脉冲四波混频实验中，测量了光谱可见光区相干激发和发射频率的相关性。这种测量可以被认为是二维核磁共振的光学模拟，因为它揭示了线性吸收光谱中被遮挡的电子跃迁之间的耦合。这种耦合是天然和人造太阳能收集器中能量和电荷传输的基本机制，因此需要描述和理解。此外，该实验还通过改变脉冲间的时间间隔，以飞秒分辨率解决了分子组装中能量流的时间演化问题。这项实验的扩展包括偏振分辨数据，将引入2D光谱和分子结构之间的关联，从而揭示生色团的空间排列。我们将应用2DES来阐明多血红素蛋白质和人工卟啉阵列中的激发动力学，这两者都在太阳能转换方案中扮演着重要的角色，后者可以作为分子电子学中的分子导线。2DES将首次提供对这些分子材料中能量传输路径和机制的直接测量。这一点与结构的关联如何将为未来的设计策略提供参考。此外，许多血红素蛋白具有未知或有争议的结构，因此2DES将提供新的结构数据。简而言之，2DES对电子结构的影响就像2D核磁共振对核结构的影响一样。接下来的两个实验报告了激发后电子激发分子的拉曼光谱和红外光谱随时间的变化。激发态动力学是光激活分子器件的重要组成部分，它们通过形状或电荷的变化在光能和机械能之间转换。振动光谱学提供了原子核结构的详细图像，这种实时测量使我们能够跟踪作为分子机器运动驱动力的结构变化。建立了时间分辨相干拉曼实验(FSRS)。我们将开发的瞬时红外测量将允许在可见光区域进行红外检测，使用与拉曼相同的检测设备。这种新方法克服了传统红外探测器有限的光谱分辨率，并将允许观察到伴随着单一电子表面结构变化的键长和键角的细微变化。这些工具将被用于研究分子马达和分子开关在各种环境中的运行机制。

Ultrafast laser technology has advanced to the extent that experiments of a complexity which was unimaginable only a few years ago now fall within the realms of the possible, and have the potential to become routine. Modern solid state laser sources produce ultrastable pulses a few million billionths of a second wide with extreme stability over most of the electromagnetic spectrum. This opens up almost any atomic or molecular process to real time interrogation. In this proposal we describe three experiments at the cutting edge of advanced laser spectroscopy. Our objective is to develop and apply these experiments to important problems in molecular and biomolecular science, with a view to demonstrating their utility in, and with the objective of establishing them as important new tools for, materials characterisation. To this end we have established collaborations with world leading laboratories in molecular and biomolecular materials science who will be the first users of the new methods.The first experiment, 2D electronic spectroscopy(ES), is a unique tool for the study of electronic coupling and energy transport in (bio-)molecular assemblies. These processes are central to the collection and utilization of solar energy and in the operation of photoactivated nanomaterials. The experiment measures the correlation of the coherent excitation and emission frequencies in the visible region of the spectrum in a three pulse four wave mixing experiment. The measurement can be thought of as the optical analog of 2D NMR, in that it reveals couplings between electronic transitions that are obscured in the linear absorption spectrum. Such couplings are the underlying mechanism for energy and charge transport in both natural and artificial solar energy collectors, and thus need to be characterised and understood. In addition the same experiment resolves the temporal evolution of the energy flow in the molecular assembly with femtosecond resolution by varying the inter-pulse timings. An extension of this experiment to include polarization resolved data, will introduce a correlation between 2D spectra and molecular structure, and thus reveal the spatial arrangement of the chromophores. We will apply 2DES to elucidate excitation dynamics in multi-heme proteins and artificial porphyrin arrays, both of which figure prominently in solar energy conversion schemes and the latter can act as molecular wires in molecular electronics. The 2DES will provide the first direct measurement of the route and mechanism of energy transport in these molecular materials. How this correlates with structure will inform future designs strategies. In addition many heme proteins have unknown or disputed structures, so 2DES will provide new structural data. In short, 2DES has the power do for electronic structure what 2D NMR has done for nuclear structure.The next two experiments report Raman and IR spectra of electronically excited molecules as a function of time after excitation. Excited state dynamics are a critical component of photoactivated molecular devices, where they act as transducer between optical and mechanical energy, by means of changes in shape or charge. Vibrational spectroscopy yields a detailed picture of the nuclear structure, and such measurements in real time allow us to track the structural changes which act as the driving force for motion in molecular machines. The time resolved coherent Raman experiment (FSRS) is well established. The transient IR measurement we will develop will permit IR detection in the visible region, using the same detection apparatus as Raman. This new method overcomes the limited spectral resolution of traditional IR detectors, and will permit the observation of subtle changes in bond lengths and angles which accompany structural change on a single electronic surface. These tools will be applied to investigate the mechanism of operation of molecular motors and molecular switches in a variety of environments.