Angular dependence of the u.v. absorption maximum wavelength in exciton coupling systems

It is shown from the u.v. data for various bis[(p-dimethlamino)benzoates] that in exciton coupling systems if the angle between two electric transition moments is larger than 90°, the u.v. λmax is shifted to longer wavelengths relative to that of the mono[(p-dimethylamino)benzoate], while if the angle is less than 90°, the u.v. λmax is shifted to shorter wavelengths.