Quantum chemical parametrization and spectroscopic characterization of the Frenkel exciton Hamiltonian for a J-aggregate forming perylene bisimide dye.

Quantum chemical and quantum dynamical calculations are performed for a bay-substituted perylene bisimide dye up to its hexameric aggregate. The aggregate structure is determined by employing the self-consistent charge density functional tight-binding (SCC-DFTB) approach including dispersion corrections. It is characterized by a stabilization via two chains of hydrogen bonds facilitated by amide functionalities. Focusing on the central embedded dimer, the Coulomb coupling for this J-aggregate is determined by means of the time-dependent density functional theory (TDDFT) to be -514 cm(-1). Exciton vibrational coupling is treated within the shifted oscillator model from which five strongly coupled modes per monomer are selected for inclusion into a minimal dynamic model. Performing wave packet propagations for a model employing up to 7 electronic states and 30 vibrational modes using the multiconfiguration time-dependent Hartree method, aggregate absorption spectra are obtained and compared to experiment.