Frenkel excitons in disordered chromophore complexes: Theory of optical absorption of Langmuir–Blodgett layers including pheophorbide-a

Abstract

Absorption spectra of dye molecules embedded in a Langmuir–Blodgett layer are simulated within a Frenkel-exciton theory. The spectra are determined in using a time-dependent formulation based on the exciton density matrix. Disorder with respect to the positions and the excitation energy of the dye molecules is accounted for within a numerical Monte Carlo treatment. The approach is used to interpret recent measurements on behenic acid layers including pheophorbide-a in a monomeric as well as dimeric form. The concrete type of aggregation and the degree of diagonal disorder can be clarified. Multilayer systems are also discussed.