University of East Anglia - Equipment Account

超快激光技术已经发展到这样的程度：几年前还难以想象的复杂实验，现在已经成为可能，并有可能成为常规。现代固体激光源产生的超稳定脉冲宽度为几百万亿分之一秒，在大多数电磁波谱上都具有极高的稳定性。这使得几乎任何原子或分子过程都可以进行实时查询。在这个提议中，我们描述了在先进激光光谱学前沿的三个实验。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方面的效用，并将它们作为重要的新工具。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，他们将成为新方法的首批用户。第一个实验，二维电子能谱（ES），是研究（生物）分子组件中电子耦合和能量传递的独特工具。这些过程对太阳能的收集和利用以及光活化纳米材料的操作至关重要。在三脉冲四波混频实验中，测量了光谱可见区相干激发频率与发射频率的相关性。测量可以被认为是二维核磁共振的光学模拟，因为它揭示了在线性吸收光谱中模糊的电子跃迁之间的耦合。这种耦合是自然和人工太阳能集热器中能量和电荷传输的潜在机制，因此需要表征和理解。此外，该实验通过改变脉冲间时间，以飞秒分辨率解决了分子组装中能量流的时间演变。将该实验扩展到包括偏振分辨数据，将引入二维光谱与分子结构之间的相关性，从而揭示发色团的空间排列。我们将应用2DES来阐明多血红素蛋白和人工卟啉阵列的激发动力学，这两者在太阳能转换方案中都占有重要地位，后者可以作为分子电子学中的分子线。2DES将首次直接测量这些分子材料中能量传输的途径和机制。这与结构的关系将为未来的设计策略提供信息。此外，许多血红素蛋白存在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 NMR对核结构的影响一样。接下来的两个实验报告了电子激发分子的拉曼和红外光谱作为激发后时间的函数。激发态动力学是光激活分子器件的关键组成部分，它们通过形状或电荷的变化充当光能和机械能之间的换能器。振动光谱学产生了核结构的详细图像，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。时间分辨相干拉曼实验（FSRS）已经建立。我们将开发的瞬态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，并将允许在单个电子表面上观察伴随结构变化的键长和角度的细微变化。这些工具将被应用于研究分子马达和分子开关在各种环境中的运作机制。

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.