Corrole-Porphyrin Conjugates with Interchangeable Metal Centers

Abstract

Oligoporphyrinoid materials composed of two or three tetrapyrrolic macrocycles have been synthesized by either mono- or disubstitution (SNAr) of a phenolic Zn-AB3-porphyrin on a meso-dichloropyrimidinyl-substituted Cu-AB2-corrole. Selective metallation/demetallation sequences were carried out on these mixed corroleporphyrin conjugates to afford multichromophoric systems with variable metal centers. The absorption spectra of the free-base corroleporphyrin systems were essentially additive, which demonstrates that only weak intercomponent interactions take place in these assemblies and therefore they can be regarded as supramolecular systems. Photophysical studies of the free-base conjugates showed that these species are highly fluorescent, with fluorescence occurring from the lowest-energy singlet state of the porphyrin subunit(s), which is (are) the lowest-energy state(s) of the assemblies. Pump-probe transient absorption spectroscopy experiments demonstrated that very efficient (>95?%) corrole-to-porphyrin singletsinglet energy transfer takes place in these pyrimidinyl-bridged multichromophoric systems by a coulombic mechanism with rate constants on the picosecond timescale.