Development of Transient Infrared Spectroscopy

该合同为瞬态红外光谱仪的开发提供了部分支持。辐射诱导的大分子合成和修饰对许多技术至关重要，从涉及特定位点的组合工艺，发色团诱导的聚合物光降解作为激活步骤，到成像，光刻，立体光刻和各种快速干燥印刷/涂层系统。了解大分子组装中发生的能量和电子转移的机制是这项工作的重要组成部分，因为几乎所有类型的光诱导反应都涉及能量转移或电子转移作为基本步骤。监测这些过程动力学的能力对于理解和控制从多肽组装到光激活合成药物等材料中的化学事件是必要的。该项目包括两名高级教师的持续合作，他们分别在聚合物光化学、立体光刻和三维成像以及光过程动力学方面进行广泛的研究，以及一个专注于研究合理合成多肽组装中的电子转移过程的项目。该仪器将通过监测亚微秒时间域内红外吸收的出现和/或消失来研究光诱导过程。一般来说，该仪器将采用激光闪光光解在小分子和大分子薄膜中产生反应性中间体，并将使用红外吸收光谱对其进行动力学分析。该仪器建成后，将允许对聚合物光降解过程的起始步骤进行实时机理研究，并提供导致聚合物性质变化的化学反应的直接评估。该仪器还将用于分析光引发剂系统，为聚合物薄膜的改性开发新的反应功能，并开发新的成像方法。其他用途包括研究质子耦合电子转移（PCET）反应，该反应在生物能量转换中起着重要作用，但其机制仍然知之甚少。这些研究将通过监测光谱中酰胺I （1630 - 1700 cm-1）和酰胺II （1510 - 1560 cm-1）区域内红外信号的动力学响应，研究氢键肽界面在控制合成蛋白质光诱导电子转移速率中的作用。最后，该仪器将用于研究Fe（II）和Co（II）卟啉中NO的光诱导解离。在这些实验中，M-NO键断裂导致游离NO产生的数量可以通过5.87-6.55 um （1525-1690 cm-1）区域（金属依赖）M-NO吸收强度的损失和NO键拉伸频率5.37um （1860 cm-1）强度的增长来监测。总之，该仪器将在适当的情况下用于即时评估形成的化学物质的性质，改进在它们形成时定位分离活性实体的策略，了解聚合物光降解，并检查各种光引发事件的动力学。构建的仪器将使用新合成的聚合物体系进行测试，例如苯乙烯，聚酯和其他含有发色团的聚合物，这些聚合物在溶液中已经详细研究了光化学。%%%***

9803006NeckersThis award provides partial support for the development of a transient infrared spectrometer. Radiation-induced macromolecular synthesis and modification is critical to many technologies, ranging from combinatorial processes that involve site specific, chromophore-induced polymer photodegradation as the activating step to imaging, lithography, stereolithography, and a variety of rapidly drying printing/coating systems. Understanding the mechanisms of energy and electron transfer occurring in macromolecular assemblies is an important component of this work, as virtually every type of photoinduced reaction involves either energy transfer or electron transfer as an elementary step. The ability to monitor the kinetics of such processes is necessary to understand, and control, chemical events in materials ranging from polypeptide assemblies to photoactivated synthetic drugs. This project includes ongoing collaborations involving two senior faculty who, respectively, carry on broad programs in polymer photochemistry, stereolithography and three dimensional imaging, and on photoprocess dynamics, as well as a program focussing on studying electron transfer processes in rationally synthesized polypeptide assemblies. The instrumentation will be used to study photoinduced processes by monitoring the appearance and /or disappearance of infrared absoptions within the sub-microsecond time domain. In general, the instrument will employ laser flash photolysis to produce reactive intermediates in small molecules and films of macromolecules, and will use infrared absorption spectroscopy for their kinetic analysis. When constructed, the instrument will allow mechanistic studies to be conducted of the initiation steps of polymer photodegradation processes in real time, and provide direct assessment of the chemical reactions leading to changes in polymer properties. The instrument will also be used to analyze photoinitiator systems, to develop new reactive functionalities for the modification of polymer thin films, and to develop new imaging methodology. Other uses include the study of proton coupled electron transfer (PCET) reactions which play an important role in biological energy conversion, but whose mechnisms remain poorly understood. These studies will examine the role of a hyrogen-bonded peptide interface in controlling the rates of photoinduced electron-transfer in synthetic proteins by monitoring the kinetic response of the IR signals occurring within the amide I (1630 - 1700 cm-1) and amide II (1510 - 1560 cm-1) regions of the spectrum. Finally, the instrument will be used to study the photoinduced dissociation of NO from Fe(II) and Co(II) porphyrins. In these experiments, the amount of M-NO bond breaking leading to free NO production can be monitored by the loss of intensity of the M-NO absorption in the 5.87-6.55 um (1525-1690 cm-1) region (metal-dependent) and the growth of intensity at the NO bond stretching frequency 5.37um (1860 cm-1).In summary, the instrument will, as appropriate, be used to instantaneously evaluate the properties of formed chemical species, improve strategies to site isolate reactive entities as they are formed, understand polymer photodegration, and examine the kinetics of a variety of photoinitiated events. The constructed instrument will be tested using newly synthesized polymer systems such as styrenes, polyesters and other polymers containing chromophores for which the photochemistry has been studied in detail in solution.%%%***