Photoinduced intramolecular charge separation in an anthraquinone-linked all-cis 5, 10, 15, 20-meso-tetrakis (2-aminophenyl)porphyrin derivative studied by picosecond and nanosecond laser spectroscopy

Abstract

Picosecond and nanosecond laser photolyses of an acetyl-linked all-cis 5, 10, 15, 20-meso-tetrakis(2-aminophenyl) porphyrin derivative (XTAPP–Ac) in acetonitrile and N,N-dimethylacetamide at room temperature reveal that the lowest excited singlet state of XTAPP–Ac is the locally excited singlet state of the porphyrin moiety; this locally excited singlet state not only decays to the ground state (via radiative and non-radiative transitions) but also undergoes intersystem crossing to the lowest excited triplet state of XTAPP–Ac. For an anthraquinone-linked compound (XTAPP–AQ), however, it is proposed that a rapid interconversion between the locally excited singlet state (¹XTAPP*–AQ) of the porphyrin moiety and the charge-separated singlet state [¹(XTAPP^˙+–AQ^˙–) produced by electron transfer from the porphyrin to anthraquinone moieties] is reached within a delay time of ca. 10 ps, although the centre-to-centre distance between these two moieties is 8.8 Å. No effective intersystem crossing from ¹(XTAPP^˙+–AQ^˙–) to its triplet state is observed.