The theory of the electronic spectra of aromatic hydrocarbon dimers

The changes of the electronic transition energies which occur on dimerization of naphthalene, anthracene, pyrene and perylene, have been calculated. It has been found that the observed spectral changes cannot be understood unless the overlap of orbitals of the two monomers is included in the calculation. Good agreement between the observed and calculated fluorescence spectrum is obtained if it is assumed that in the fluorescent state of the dimer the interplanar separation of the monomers is approximately 3 å.