Triplet Energy Transfers in Well-Defined Host Guest Porphyrin-Carboxylate/Cluster Assemblies

摘要

The dyes (5-(4-carboxylphenyl)-10,15,20-tritolylporphyrinato)zinc(II) (MCP) and (5,15-bis(4-carboxylphenyl)-15,20-ditolylporphyrinato)zinc(II) (DCP), as their sodium salts, were used to form assemblies with the unsaturated cluster Pd-3(dppm)(3)(CO)(2)+ ([Pd-3(2+)], dppm = (Ph2P)(2)CH2) via ionic CO2-Pd-3(2+) interactions. The photophysical properties in their triplet states were studied. The position of the T-1 state of [Pd-3(2+)] (similar to 8190 cm(-1)) has been proposed using DFT computations and was corroborated by the presence of a T-n -700 nm arising from a T1-T1 annihilation process at 77 K. The static quenching of the near-IR phosphorescence of the dyes at 785 nm (T1 -> S-0) was observed. Thermodynamically poor reductive and oxidative driving forces render the photoinduced electron transfer quenching process either inoperative or very slow in the T-1 states. Instead, slow to medium T-1-T-1 energy transfer ((3)dye*...[Pd-3(2+)] -> dye...3[Pd-3(2+)]*) operates through a Forster mechanism exclusively with k(ET) values of similar to 1 X 105 s(-1) on the basis of transient absorption measurements at 298 K.