Coherent Multidimensional Optical Spectroscopy of Excitons in Molecular Aggregates; Quasiparticle versus Supermolecule Perspectives

Coherent multidimensional optical spectroscopy of excitons in molecular aggregates was reported. It was found that molecular aggregates formed spontaneously in concentrated solutions and on surfaces, and can be synthesized using supramolecular chemistry techniques. Various types of structure of aggregates included one-dimensional strands, two-dimensional layers, circular complexes, cylindrical nanotubes, multiwall cylinders and supercylinders, branched fractal structures, dendrimers, and disordered globular complexes. It was also reported that aggregates could be fabricated on substrates by 'dip-pen' technology. Their absorption spectra had two bands, whose intensities and Davydov splitting were related to the intermolecular interaction strength and the relative orientation. It was concluded that excitons in large aggregates can be delocalized across many chromophores.