Electronic Spectroscopy of Mixed Cyclophanes: [2.2](9,10)Anthraceno(1,4)naphthalenophane

Abstract

The absorption and fluorescence spectra of [2.21(9,10) anthraceno (1,4) naphthalenophane are reported. The anisotropy of the absorption bands was measured by two methods, ( i ) from fluorescence polarization ratios in a rigid glass and (ii) from single crystal absorption spectra at 23 K. The two states arising from the ¹L_a states of the two chromophores were identified together with two states arising from other chromophore ¹B_2u states. Two states arising from the ¹L_a states of the two chromophores were also identified. Whereas a coupled chromophore model accounts reasonably well for the latter two states, the energies and intensities of the bands arising from ¹L_a chromophore states cannot be reconciled with this approach. Long axis polarized absorption intensity lying under the ¹L_a, bands appears to be vibronically induced and not due to the ¹L_b states. The absorption spectrum, fluorescence spectrum and fluorescence polarization ratios of a stable dimer were also observed. Its structure is similar to that of the stable dimer of anthracene in which the molecular long axes are parallel but the short axes make an angle of about 70º with each other.