Investigation of the photophysical and eletrochemical properties of a free base tetrapyridyl porphyrin with meso carbon linked ruthenium (II) groups

Here a systematic investigation on a regular type of porphyrin with outlying ruthenium groups, ({H2TPyP [Ru(terpy)(PPh3)(2)](4)}8PF(6)), and the isolated ruthenium substituent ([RuCl(terpy)(PPh3)(2)]PF6) is reported. Steady state as well as time-resolved fluorescence and absorbance were employed in association with cyclic voltammetry. The steady state spectroscopy data suggest that the outlying ruthenium groups mostly interact with the second excited singlet state orbitals of the porphyrin ring, while the lowest singlet excited state electronic properties are weakly perturbed. Moreover, attachment of peripheral groups highly suggests the appearance of additional vibrational modes in the molecule, which leads to new internal conversion decay pathways that quenches both the radiative deactivation and the intersystem crossing to form the porphyrin triplet excited states. Transient absorption and electrochemical data reveal the absence of charge transfer between the porphyrin ring and ruthenium moieties. Energy transfer to the porphyrin ring is possible but not enough to efficiently quench the excited state of the ruthenium sites. Finally, our results shine light about future molecular engineering strategies that can be employed with the aim to obtain efficient light harvesting tetraruthenated porphyrin molecules. (C) 2015 Elsevier B.V. All rights reserved.