You can append on me! Porphyrin-appended polynorbornenes derived from 5,6-endo-fused N-arylpyrrolidenonorbornenes have been shown to have coherently aligned pendant groups that exhibit exciton coupling and fluorescence quenching in the absorption and emission profiles (see figure).
Six different kinds of coherently aligned porphyrin-appended polynorbornenes derived from 5,6-endo-fused N-arylpyrrolidenonorbornenes have been synthesized. π–π interactions between the pendant groups are essential for dictating the photophysical properties of the polymers and the mechanism for the stereoselective formation of polymers. Splitting of the Soret band of polymers 2 a–c, which have alkyl-substituted porphyrin pendant groups, suggests strong exciton coupling between chromophores. No splitting of the Soret band is observed for polymers 2 d–f, which have tetraaryl substituents on the porphyrin moiety. Significant fluorescence quenching is found in polymers 2 a–e, whereas only slightly reduced quantum yield is observed for 2 f. Time-resolved fluorescence measurements also indicate a similar trend. The AFM image of 2 d on graphite shows aggregation to form a two-dimensional, ordered pattern.