Association Complexes between Cationic Metallophthalocyanines and Anionic Metalloporphyrins I: Spectrometric Studies of Electronic Interactions

Abstract

The formation and spectroscopic properties of several metalloporphyrin−metallophthalocyanine complexes have been investigated. The complexes consist of negatively charged tetrasulfonatophenyl or tetracarboxyphenyl porphyrins in ion pairs with positively charged crown ether substituted metallophthalocyanines. The positive charge was delivered to the modified phthalocyanine molecules by inserting potassium ions into the crown ether cavities. The complexes were formed by mixing the constituent tetrapyrrole compounds in DMSO or ethanol. UV−vis spectrophotometric studies of the ground-state complexes showed loss of the metallophthalocyanine spectrum and the appearance of new spectral bands at longer wavelengths, indicating strong electronic coupling between the components. Analysis of the porphyrin−phthalocyanine complex by the method of continuous variations revealed formation of dimeric and trimeric species. Cyclic voltammetric and spectroelectrochemistry experiments indicated a degree of partial charge transfer character for the ground-state complexes. The free-base/free-base complex showed emission only from the charge transfer state, regardless of the excitation wavelength. The lifetime of the charge transfer state was 3.65 ns. Ultrafast transient absorption studies of the free-base/free-base complex showed that the charge transfer state was fully formed in less than 5 ps after excitation at either 400 or 720 nm. The observed transients were independent of the excitation wavelength and showed little decay on the 500 ps time scale, consistent with the observed fluorescence lifetime.