Exciton scattering approach for optical spectra calculations in branched conjugated macromolecules

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• 作者：Hao Li^a ; Chao Wu^b ; Sergey V. Malinin^c ; Sergei Tretiak^d ; ^e ; ^{serg@lanl.gov} ; Vladimir Y. Chernyak^c ; ^{chernyak@chem.wayne.edu}
• 关键词：Exciton ; Scattering ; Conjugation ; Dendrimers ; Electronic excitations ; Excited states ; Branched structures ; ES approach ; Scattering phase ; Transition dipoles
• 刊名：Chemical Physics
• 出版年：2016
• 出版时间：20 December 2016
• 年：2016
• 卷：481
• 期：Complete
• 页码：124-132
• 全文大小：4120 K
• 卷排序：481

文摘

The exciton scattering (ES) technique is a multiscale approach based on the concept of a particle in a box and developed for efficient calculations of excited-state electronic structure and optical spectra in low-dimensional conjugated macromolecules. Within the ES method, electronic excitations in molecular structure are attributed to standing waves representing quantum quasi-particles (excitons), which reside on the graph whose edges and nodes stand for the molecular linear segments and vertices, respectively. Exciton propagation on the linear segments is characterized by the exciton dispersion, whereas exciton scattering at the branching centers is determined by the energy-dependent scattering matrices. Using these ES energetic parameters, the excitation energies are then found by solving a set of generalized “particle in a box” problems on the graph that represents the molecule. Similarly, unique energy-dependent ES dipolar parameters permit calculations of the corresponding oscillator strengths, thus, completing optical spectra modeling. Both the energetic and dipolar parameters can be extracted from quantum-chemical computations in small molecular fragments and tabulated in the ES library for further applications. Subsequently, spectroscopic modeling for any macrostructure within a considered molecular family could be performed with negligible numerical effort. We demonstrate the ES method application to molecular families of branched conjugated phenylacetylenes and ladder poly-para-phenylenes, as well as structures with electron donor and acceptor chemical substituents. Time-dependent density functional theory (TD-DFT) is used as a reference model for electronic structure. The ES calculations accurately reproduce the optical spectra compared to the reference quantum chemistry results, and make possible to predict spectra of complex macromolecules, where conventional electronic structure calculations are unfeasible.