The Spectral Signatures of Frenkel Polarons in H- and J-Aggregates

作者：Frank C. Spano · 发表于：Accounts of Chemical Research · 年份：2009 · DOI：10.1021/ar900233v · 被引用次数：1722 · 研究领域：Organic Electronics and Photovoltaics、Spectroscopy and Quantum Chemical Studies、Photochemistry and Electron Transfer Studies

Electronic excitations in small aggregates, thin films, and crystals of conjugated organic molecules play a fundamental role in the operation of a wide array of organic-based devices including solar cells, transistors, and light-emitting diodes. Such excitations, or excitons, are generally spread out over several molecules: a balance between the delocalizing influence of resonant intermolecular coupling and the localizing influence of static and dynamic disorder determines the coherence range of the exciton. Because of the "soft" nature of organic materials, significant nuclear relaxation in the participating molecules also accompanies the electronic excitations. To properly understand energy or charge transport, one must treat intermolecular (excitonic) coupling, electron-vibrational coupling, and disorder on equal footing. In this Account, we review the key elements of a theoretical approach based on a multiparticle representation that describes electronic excitations in organic materials as vibronic excitations surrounded by a field of vibrational excitations. Such composite excitations are appropriately called Frenkel excitonic polarons. For many conjugated molecules, the bulk of the nuclear reorganization energy following electronic excitation arises from the elongation of a symmetric vinyl stretching mode with energy approximately 1400 cm(-1). To appreciate the impact of aggregation, we study how the vibronic progression of this mode, which dominates the isolated (solva...