Very fast singlet and triplet energy transfers in a tri-chromophoric porphyrin dyad aided by the truxene platform

A trichromophoric dyad composed of an octa-beta-alkyl-palladium(II)porphyrin (donor) and two tri-meso-aryl-zinc(II)porphyrins (acceptors) held by a truxene spacer exhibits very fast rates for triplet energy transfers at 77 (k(ET)(T-1) = 1.63 x 10(8) s(-1)) and 298 K (k(ET) (T-1) = 3.44 x 10(8) s(-1)), whereas the corresponding singlet energy transfer rates, k(ET)(S-1) = 3.9 x 10(10) s(-1) (77 K) and k(ET) (S-1) = 6.0 x 10(10) s(-1) (298 K), are also considered fast. The interpretation for these results is that the energy transfer processes proceed via a through bond Dexter mechanism (i.e. double electron exchange) supported by comparison with literature data and evidence for a moderate MO coupling between the donor and acceptor chromophores in the frontier MOs.