ELECTRONIC SPECTROSCOPY OF SIMPLE PORPHYRINS AND BACTERIORHODOPSIN

本提案中所述的研究是一种延续、延伸和 修改我们目前的MBRS赠款下正在进行的工作。 这是一个简单的卟啉在固态在5K的研究， 它们的电子基态和激发态性质， 激发，光学烧孔和斯塔克效应。 根本 推动这项研究的假设是，激发态和 低能量Npi * 跃迁的存在。 在我们工作的这一阶段， 将研究这些分子的游离碱和金属络合物形式：例如， 卟吩二氢卟酚四氮杂菲 这些简单的卟啉是 生物医学上重要部分的化合物（例如血红素，细胞色素， 叶绿素和光动力光敏剂）。 卟啉是并且具有 然而，大多数光谱数据都来自室内， 温度解决方案，只产生宽带。 我们的做法是 将分子置于正烷烃基质晶体中;在液氦中 温度高分辨率（约2cm-1）的光谱。 的 然后，在特定晶体环境中的分子的光谱可以被 通过使用单点激励来隔离。 这种高分辨率可以 通过使用光学烧孔技术得到了进一步的改进。 当一个分子 溶解在基质中，其电子光谱是不均匀的， 当窄带宽激光器用于激发时， 有时可能在不均匀加宽的带中烧孔; 空穴由光化学、瞬时存储或分子 重新定位 当单点光谱的窄带，或光学 空穴与斯塔克效应相结合，它们提供了一个敏感的问题， 分子电子态 我们的总体方法包括 单混合晶体（卟啉/正烷烃）或低温 玻璃状溶液 将样品浸入液氮或氦中， 获得的吸收或发射光谱。 单点光谱是由或 用窄带激光烧蚀和扫描光学孔。 为了斯塔克 在实验中，将一个圆锥形取向的晶体放置在 个电极 电场可以是直流的或脉冲的 取决于需要。 该项目的主要长期目标是 使用这些技术来提取详细的激发态信息 (e.g.,振动能，偶极矩，π π * 和npi * 原点 能量、耦合等） 从这些重要的生物医学发色团中分离出来。 (Of现在特别有趣的是，我们似乎找到了有力的证据， 对于其中一些中存在低能量pi * 较小的-n跃迁， 简单卟啉）。 这项研究将涉及两名MBRS学生。 每个 一个将负责一个单独的发色团，并将执行其 制备、纯化和运行低和中分辨率光谱。 激光 斯塔克实验将由私家侦探完成 大多数光谱 目前关于这些发色团的数据分辨率很低，因为 电子能带的显著不均匀加宽。 光学 空穴燃烧、单点激发和斯塔克效应将提供一种 更清楚地了解这些生物医学上重要的 分子。

The research described in this proposal is a continuation, extention and modification of the work being carried out under our current MBRS grant. It is a study of simple porphyrins in the solid-state at 5K with respect to their electronic ground and excited state properties using single site excitation, optical hole-burning and the Stark effect. The fundamental hypothesis driving this research is that the excited states and the presence of low energy Npi* transitions. In this phase of our work both free base and metal complex forms of these molecules will be studied: e.g. porphin, chlorin, tetraazaporphin. These simple porphyrins are the parent compounds of biomedically important moieties (e.g. hemes, cytochromes, chlorophylls and photodynamic photosensitizers). Porphyrins are and have been actively studied, however most of the spectroscopic data sis from room temperature solutions which yield only broad bands. Our approach is to place the molecules in n-alkane host crystals; at liquid helium temperatures highly resolved (about 2 cm-1) spectra are obtained. The spectrum of molecules in a particular crystal environment can then be isolated by using single site-excitation. This high resolution can be improved even more by using optical hole-burning. When a molecule is dissolved in a matrix, its electronic spectrum is inhomogeneously broadened; when a narrow bandwidth laser is employed for excitation it is sometimes possible to burn holes in the inhomogeneously broadened bands; holes result from photochemistry, transient storage or molecular reorientation. When the narrow bands of single site spectra, or optical holes are coupled with the Stark effect, they provide a sensitive proble of molecular electronic states. Our overall methodology involves the growth of single mixed crystals (porphyrin/n-alkane) or making low temperature glassy solutions. The sample is immersed in liquid N2 or He and an absorption or emission spectrum obtained. Single site spectra are made or optical holes burned and scanned with a narrow band laser. For Stark effect experiments, a coniscopically oriented crystal is placed between electrodes. The electric field can be applied either DC or pulsed depending on the need. The primary long-term objective of this project is to use these techniques to extract detailed excited state information (e.g., vibrational energies, dipole moments, pi pi* and npi* origin energies, coupling, etc.) from these biomedically important chromophores. (Of particular interest now is that we seem to be finding strong evidence for the presence of low energy pi* lesser--- n transitions in some of these simple porphyrins). This research will involve two MBRS students. Each one will be responsible for a separate chromophore and will carry out its preparation, purification and run low and medium resolution spectra. Laser and Stark experiments will be done with the PI. Most of the spectroscopic data now available on these chromophores is low resolution because of substantial inhomogeneous broadening of the electronic bands. Optical hole-burning, single site excitation and the Stark effect will provide a clearer picture of the electronic states of these biomedically important molecules.