On the Splittings of J-Aggregate Band in Pseudoisocyanine

The observation of J-band splittings in the Fano–DeVoe type calculations of pseudoisocyanine aggregates is reported. Based upon the monoclinic structure of pseudoisocyanine iodide crystal, we build four models which respectively assume the lattice constants of the crystal structure. The one-dimensional (1D-) single polymer model is selected along a particular direction from the crystal structure. As we diminish the lattice constants uniformly, the 1D-single-polymer model comes to reproduce single J-bands, while two kinds of 2D-two-inter-polymer interaction models resolve the single J-bands into doublet through multiplet structures for the corresponding parameters. The 3D-four-inter-polymer interaction model brings about doubly split J-bands, but the shortening of the parameters resolves the doublet J-bands into quartet through multiplet structures. However, a single J-band is obtained by the assumption of an orthorhombic 3D-four-inter-polymer model which has the same parameters as those of the monoclinic iodide crystal except for the angle. The shapes calculated are found to be extremely sensitive to the geometrical values as well as the monomer spectroscopic parameters. The cause of the J-band splittings is ascribable to the excitonic interactions between at least two column polymers.