The J- and H-bands of dye aggregate spectra: Analysis of the coherent exciton scattering (CES) approximation

The validity of the CES approximation is investigated by comparison with direct diagonalisation of a model vibronic Hamiltonian of N identical monomers interacting electronically. Even for quite short aggregates (N≳6) the CES approximation is shown to give results in agreement with direct diagonalisation, for all coupling strengths, except that of intermediate positive coupling (the H-band region). However, previously excellent agreement of CES calculations and measured spectra in the H-band region was obtained [A. Eisfeld, J.S. Briggs, Chem. Phys. 324 (2006) 376]. This is shown to arise from use of the measured monomer spectrum which includes implicitly dissipative effects not present in the model calculation.