Abstract Two polycyclic aromatics having a phenyl-substituted pentahelicene moiety, 13, 14- diphenyldibenzo [c, g] chrysene (19) and 14, 15-diphenyldibenzo [f, j] picene (38) have been obtained by irradiation of the appropriate diarylethylenes (13 and 18). Further irradiation of 19 in benzene yields mainly dibenzo [a, g] coronene (21) by cyclodehydrogenation with simultaneous loss of a phenyl substituent. The side products of this reaction are probably ...