Terenziani Francesca, Painelli Anna, Katan Claudine, Charlot Marina, Blanchard-Desce Mireille
Dipartimento di Chimica GIAF, Università di Parma and INSTM-UdR Parma, Parco Area delle Scienze 17/a, 43100 Parma, Italy.
J Am Chem Soc. 2006 Dec 13;128(49):15742-55. doi: 10.1021/ja064521j.
We present a joint theoretical and experimental work aimed to understand the spectroscopic behavior of multipolar dyes of interest for nonlinear optics (NLO) applications. In particular, we focus on the occurrence of broken-symmetry states in quadrupolar organic dyes and their spectroscopic consequences. To gain a unified description, we have developed a model based on a few-state description of the charge-transfer processes characterizing the low-energy physics of these systems. The model takes into account the coupling between electrons and slow degrees of freedom, namely, molecular vibrations and polar solvation coordinates. We predict the occurrence of symmetry breaking in either the ground or first excited state. In this respect, quadrupolar chromophores are classified in three different classes, with distinctively different spectroscopic behavior. Cases of true and false symmetry breaking are discriminated and discussed by making resort to nonadiabatic calculations. The theoretical model is applied to three representative quadrupolar chromophores: their qualitatively different solvatochromic properties are connected to the presence or absence of broken-symmetry states and related to two-photon absorption (TPA) cross-sections. The proposed approach provides useful guidelines for the synthesis of dyes for TPA application and represents a general and unifying reference frame to understand energy-transfer processes in multipolar molecular systems, offering important clues to understand basic properties of materials of interest for NLO and energy-harvesting applications.
我们展示了一项理论与实验相结合的工作，旨在理解用于非线性光学（NLO）应用的多极染料的光谱行为。特别地，我们关注四极有机染料中破缺对称态的出现及其光谱后果。为了获得统一的描述，我们基于对表征这些系统低能物理的电荷转移过程的少态描述开发了一个模型。该模型考虑了电子与慢自由度之间的耦合，即分子振动和极性溶剂化坐标。我们预测了基态或第一激发态中对称破缺的出现。在这方面，四极发色团被分为三类，具有明显不同的光谱行为。通过非绝热计算区分并讨论了真对称破缺和假对称破缺的情况。将理论模型应用于三种代表性的四极发色团：它们在溶剂化显色性质上的定性差异与破缺对称态的存在与否相关，并与双光子吸收（TPA）截面有关。所提出的方法为用于TPA应用的染料合成提供了有用的指导方针，并代表了一个通用且统一的参考框架，以理解多极分子系统中的能量转移过程，为理解NLO和能量收集应用中感兴趣材料的基本性质提供了重要线索。
