Department of Chemistry, University of Central Florida, P. O. Box 162366, Orlando, FL 382616, USA.
Molecules. 2011 Apr 18;16(4):3315-37. doi: 10.3390/molecules16043315.
Many phenomena, including life itself and its biochemical foundations are fundamentally rooted in chirality. Combinatorial methodologies for catalyst discovery and optimization remain an invaluable tool for gaining access to enantiomerically pure compounds in the development of pharmaceuticals, agrochemicals, and flavors. Some exotic metamaterials exhibiting negative refractive index at optical frequencies are based on chiral structures. Chiroptical activity is commonly quantified in terms of circular dichroism (CD) and optical rotatory dispersion (ORD). However, the linear nature of these effects limits their application in the far and near-UV region in highly absorbing and scattering biological systems. In order to surmount this barrier, in recent years we made important advancements on a novel non linear, low-scatter, long-wavelength CD approach called two-photon absorption circular dichroism (TPACD). Herein we present a descriptive analysis of the optics principles behind the experimental measurement of TPACD, i.e., the double L-scan technique, and its significance using pulsed lasers. We also make an instructive examination and discuss the reliability of our theoretical-computational approach, which uses modern analytical response theory, within a Time-Dependent Density Functional Theory (TD-DFT) approach. In order to illustrate the potential of this novel spectroscopic tool, we first present the experimental and theoretical results obtained in C(2)-symmetric, axially chiral R-(+)-1,1'-bi(2-naphthol), R-BINOL, a molecule studied at the beginning of our investigation in this field. Next, we reveal some preliminary results obtained for (R)-3,3'-diphenyl-2,2'-bi-1-naphthol, R-VANOL, and (R)-2,2'-diphenyl-3,3'-(4-biphenanthrol), R-VAPOL. This family of optically active compounds has been proven to be a suitable model for the structure-property relationship study of TPACD, because its members are highly conjugated yet photo-stable, and easily derivatized at the 5- and 6-positions. With the publication of these outcomes we hope to motivate more members of the scientist community to engage in state-of-the-art TPACD spectroscopy.
许多现象，包括生命本身及其生化基础，都从根本上根植于手性。组合方法在发现和优化催化剂方面仍然是获得手性纯化合物的宝贵工具，这些化合物在手性药物、农用化学品和香料的开发中有着广泛的应用。一些具有负折射率的奇特超材料是基于手性结构的。圆二色性（CD）和旋光色散（ORD）通常用于量化手性活性。然而，这些效应的线性性质限制了它们在手性吸收和散射生物系统的远和近紫外区域的应用。为了克服这一障碍，近年来，我们在一种新的非线性、低散射、长波长 CD 方法，即双光子吸收圆二色性（TPACD）方面取得了重要进展。本文介绍了实验测量 TPACD 的光学原理，即双 L 扫描技术，及其使用脉冲激光的重要意义。我们还对我们的理论计算方法进行了有指导意义的检查和讨论，该方法使用了现代分析响应理论，并结合了时间相关密度泛函理论（TD-DFT）方法。为了说明这种新型光谱技术的潜力，我们首先介绍了在 C(2)对称、轴向手性 R-(+)-1,1'-双(2-萘酚)、R-BINOL 中获得的实验和理论结果，这是我们在该领域开始研究时研究的分子。接下来，我们揭示了一些初步结果，这些结果是在(R)-3,3'-二苯基-2,2'-联-1-萘酚、R-VANOL 和(R)-2,2'-二苯基-3,3'-(4-联二萘酚)、R-VAPOL 中获得的。这些具有光学活性的化合物已被证明是研究 TPACD 结构-性质关系的合适模型，因为其成员高度共轭但光稳定，并且易于在 5-和 6-位进行衍生化。随着这些结果的发表，我们希望激励更多的科学家参与到最先进的 TPACD 光谱学中来。
