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

TL;DR

This paper evaluates the accuracy of the coherent exciton scattering (CES) approximation in modeling dye aggregate spectra, showing it generally agrees with direct calculations except in specific coupling regions, and explains previous experimental agreement due to dissipative effects.

Contribution

It provides a detailed comparison of the CES approximation with direct diagonalisation, clarifying its validity range and explaining prior experimental correlations.

Findings

CES agrees with direct diagonalisation for aggregates with N≥6 in most coupling regimes.

Discrepancies occur in the intermediate positive coupling (H-band) region.

Previous experimental agreement is due to implicit dissipative effects in measured spectra.

Abstract

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\gtrsim 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, 376]. This is shown to arise from use of the measured monomer spectrum which includes implicitly dissipative effects not present in the model calculation.