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

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. (C) 1999 Elsevier Science B.V. All rights reserved.