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The dual fluorescence in polar solvents of 9,9'-bianthryl (BA) and of the electronically perturbed BA-derivatives 10-chloro-BA (BACI), BA-10carboxaldehyde (BAA) and N-(9-anthryl)-carbazole (C9A) as well as of N-(4-cyanophenyl)-carbazole (CBN) is analysed and interpreted in terms of a simplified microstructural solvent interaction model. Dipole moments pT relative to pT (CBN) of the fluorescent charge transfer state have been derived from the solvatochromic band shifts in nitrile and alcohol homologous solvent series and are similar for BA, BACI and C9A. This implies that the charge transfer in the excited state occurs to a maximum degree even in the symmetric molecule BA. -QCFFIPI-potential energy curves have been calculated and are used to discuss these findings. BAA fluoresces in alcohols only, pT compared to the other compounds studied being somewhat smaller probably because of specific H-bond interactions with the solvent. -Using relative fluorescence quantum yields and energetic considerations the dependence of the excited states equilibrium on both solvent polarity and solute perturbation is discussed.

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By E. CLAR and M. ZANDER.An improved synthesis of 2 : 3-10 : ll-dibenzoperylene (11) is described. This reacted easily with maleic anhydride to give the adduct (111) which was dehydrogenated to the anhydride (IV) . Decarboxylation yielded the tribenzoperylene (V). The unusually low reactivity of this hydrocarbon is related to formula (Va), which consists exclusively of benzenoid rings interlinked by quasi-single bonds.2 : 3-10 : ~~-DIBENZOPERYLENE (11) was obtained from 9 : 9'-diphenanthryl (I) in a sodium chloride-aluminium chloride melt.1 However the method gives very low yields and sometimes fails completely.2 We obtained yields of not less than 50% when the cyclisation was carried out in boiling benzene with aluminium chloride and stannic chloride as dehydrogenating agent.Recently we assumed the existence of a dissociable adduct between perylene and maleic anhydride preceding the formation of 1 : 12-benzoperylenedicarboxylic a n h ~d r i d e . ~ The two " external " benzene rings in dibenzoperylene (11) stabilise the analogous adduct