Transient absorption spectroscopy of a monofullerene C60-bis-(pyropheophorbide a) molecular system in polar and nonpolar environments

• Published in: Applied physics. B, Lasers and optics Lasers and optics, 2004-09, Vol.79 (5), p.617-622
• Main Authors: AL OMARI, S, ERMILOV, E. A, HELMREICH, M, JUX, N, HIRSCH, A, RÖDER, B
• Format: Article
• Language: English
• Subjects: Atomic and molecular physics; Atomic properties and interactions with photons; Buckminsterfullerene; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Effects of atomic and molecular interactions on electronic structure; Electronic structure of atoms, molecules and their ions: theory; Environmental and solvent effects; Exact sciences and technology; Excitation; Fluorescence; Fluorescence, phosphorescence (including quenching); Fullerenes; Fullerenes and related materials; Ground state; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Physics; Quenching; Solvents; Toluene; Visible and ultraviolet spectra
• ISSN: 0946-2171; 1432-0649
• DOI: 10.1007/s00340-004-1570-y

The population dynamics of the excited and ground states of the monofullerene-bis (pyropheophorbide a) complex (FP1) were studied in polar (DMF) and nonpolar (toluene) solvents using picosecond transient absorption techniques. A strong quenching of the fluorescence signal of FP1 was observed in both solvents, in comparison to the fluorescence of bis (pyropheophorbide a) (P2). This quenching is due to an intramolecular photoinduced electron transfer from the pyropheophorbide a (pyroPheo) moiety to the fullerene C60 monoadduct. In DMF the charge-separated (CS) state of FP1 has a lifetime of 0.32 ns and undergoes a direct transition to the ground state, resulting in a very low value of photosensitised singlet oxygen generation. In toluene, energy transfer from the first excited triplet state of pyroPheo, which has been populated via relaxation of the CS state, generates a considerable amount of singlet oxygen. The lifetime of the CS state in the nonpolar solvent was estimated to be 0.29 ns. It was also shown that in both DMF and toluene the first excited singlet state as well as the triplet state of the fullerene moiety in FP1 are not occupied.