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Thursday, November 17, 2011
2:00 PM - 3:00 PM
CNLS Conference Room (TA-3, Bldg 1690)

Postdoc Seminar

A Quasiparticle View of Electronic Excitations in Branched Conjugated Oligomers

Hao Li
T-1 and CNLS

The electronic excitations in low-dimensional macromolecules have been attributed to standing waves that represent quantum quasiparticles (excitons) scattered at molecular vertices. We develop the exciton scattering (ES) approach as an efficient theoretical tool to design macromolecules with desired optical and electronic properties. Within the ES approach, molecular repeat units, which form linear segments, are characterized by the exciton dispersion, whereas scattering at vertices is determined by the energy-dependent scattering matrices. These energetic ES parameters allow one to find the excitation energies by solving a generalized “particle in the box” problem on the graph that represents the molecule. The picture of molecular building blocks is also useful for the oscillator strength calculations. The molecular transition dipoles consist of charge and dipole contributions generated by repeat units and molecular vertices. Linear relations between the transition dipolar contributions and the exciton wave amplitudes are determined by energy-dependent dipole parameters of the building blocks. Exciton properties on different building blocks (e.g., dispersion relations, scattering matrices, and transition dipole parameters), which are necessary for the prediction of optical spectra, have been retrieved from the reference quantum chemical (QC) computations (TDDFT/TDHF) in relatively simple molecules (poly-phenylacetylenes and ladder poly-para-phenylenes). The tabulated ES parameters enable the real-time calculation for the spectrum of any molecule consists of the characterized

Host: Kipton Barros, T-4 and CNLS