Two-dimensional electronic spectra of symmetric dimers: Intermolecular coupling and conformational states.
We study the information content of two-dimensional (2D) electronic photon-echo (PE) spectra, with special emphasis on their potential to distinguish, for waiting times T=0, between different conformations of electronically coupled symmetric dimers. The analysis is performed on the basis of an analytical formula for the frequency-domain 2D PE signal. The symmetric dimers are modeled in terms of two identical, energy-degenerate, excitonically coupled pairs of electronic states in the site representation. The spectra of conformationally weighted ensembles, composed of either two or four dimers, are compared with their one-dimensional linear absorption counterparts. In order to provide a realistic coupling pattern for the ensemble consisting of four dimers, excitonic couplings are estimated on the basis of optimized geometries and site-transition dipole moments, calculated by standard semiempirical methods for the bridged bithiophene structure 1,2-bithiophene-2-yl-ethane-1,2-dion (T2[CO]2). In the framework of our model, the highly readable 2D PE spectra can unambiguously identify spectral doublets, by relating peak heights and positions with mutual orientations of site-localized transition dipoles.
Szöcs
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Institute of Chemistry, Comenius University, Mlynská dolina CH2, 842 15 Bratislava, Slovakia. szocs@fns.uniba.sk
Pálszegi
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T
Lukes
V
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Sperling
J
J
Milota
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Jakubetz
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Kauffmann
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