Photophysical properties of structurally deformed basket-handle porphyrins

The fluorescence properties of a series of structurally deformed basket-handle porphyrins in different solvents are reported. The deformation is induced by the covalent connection of the meso-phenyl groups of meso-5,10,15,20-tetraphenylporphyrin (H2TPP) via bridging groups of varying nature and chain length. The structures calculated using molecular mechanics reveal the deformation in the porphyrin ring created by short bridging groups. The distortion in the macrocycle resulted in red shifts of the emission bands, low quantum yields, high intersystem crossing rates and marked perturbed lifetimes. Maximum effects are observed for the most distorted porphyrin. A possibility for an intramolecular electron transfer is invoked in one of the systems in which the bridging phenyl group acts as an acceptor owing to the presence of electron-withdrawing substituents.