Picosecond dynamics of intramolecular singlet excitation energy transfer and photoinduced electron transfer in covalently-linked carotenoid—porphyrin and carotenoid—porphyrin—pyromellitimide molecules

Abstract

Intramolecular singlet excitation energy transfer from the carotenoid to the free base porphyrin takes place in a 1,4-phenylenebridged carotenoid-free base porphyrin in competition with rapid internal conversion (<10 ps) of the singlet excited state of carotenoid, while efficient excitation transfer from the zinc porphyrin to the carotenoid has been observed in the corresponding zinc complex. Photoexcitation of a carotenoid-free base porphyrin—pyromellitimide triad molecule (CH 2PI) leads to the formation of a charge separated state ((C) +H 2P(I) −) with a lifetime of 15 ns. Rapid accumulation of this charge separated state with 40–50 ps time constant indicates the long-distance electron transfer from the singlet excited state of carotenoid to the pyromellitimide.