Using Three-Pulse Femtosecond Spectroscopy to Probe Ultrafast Triplet Energy Transfer in Zincmeso-Tetraarylporphyrin−Perylene-3,4-dicarboximide Dyads

Abstract

Linear arrays of zinc meso-tetraarylporphyrin (ZnP), perylene-3,4-dicarboximide (PMI), and either naphthalene-1,8:4,5-bis(dicarboximide) (NI) or pyromellitimide (PI) were synthesized and studied by ultrafast transient absorption spectroscopy. PMI was covalently linked in one of two orientations relative to ZnP. In one set of molecules, the 9 position of the perylene core is connected to the para position of a meso-phenyl in ZnP to give ZnP−PMI−N−X, where X = NI or PI is attached to the imide nitrogen atom of PMI. In the second set of compounds, the imide nitrogen atom of PMI is connected to the meso-phenyl in ZnP to give ZnP−N−PMI−X, where X = PI or H. Selective excitation of ZnP using 420 nm, 110 fs laser pulses in each molecule in toluene produces 1*ZnP, which intersystem crosses (ISC) to 3*ZnP with τ = 2.3 ns. For ZnP−PMI−N−X, triplet energy transfer (TET) from 3*ZnP to PMI is much faster than ISC, so that 3*ZnP is not observed by one-pump−one-probe transient absorption spectroscopy. Following its form...