title: Dissipation of electronic excitation energy within a C60 [6:0]-hexaadduct carrying 12 pyropheophorbide a moieties.
abstract: The synthesis and photophysical studies of a fullerene [6:0]-hexaadduct that carries 12 pyropheophorbide a units are reported. The synthesis started with the malonate 1, which was coupled under template conditions to C(60)() to give the hexaadduct 2. After removal of the protecting group with acid the dodecakis amino-substituted precursor compound 3 was generated. 3 was not isolated but directly reacted with the N-succinimid ester 4 of pyropheophorbide a (5), which delivered the desired fullerene [6:0]-hexaadduct 6 in excellent yield. The photophysical properties of 6 were studied and compared with those of the fullerene [5:1]-hexaadduct 7 with six pyropheophorbide a groups and the bispyropheophorbide a-fullerene [5:1]-hexaadduct 8. The pyropheophorbide a units in 6 undergo after light absorption very efficient energy transfer as well as partly excitonic interaction. The last process results in formation of energy traps, which could be resolved experimentally. Compared to the reference compounds 7 and 8, 6 has a higher probability of trap formation due to a higher local concentration of dye molecules and shorter distances between them. As a consequence, the excitation energy is delivered rapidly (within 23 ps) to the traps, resulting in decreases of the fluorescence, intersystem crossing, and singlet oxygen quantum yields in comparison with the values of the reference compounds.
authors.affiliation: Institut für Organische Chemie, Universität Erlangen-Nürnberg, Henkestrasse 42, D-91054 Erlangen, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Helmreich
authors.forename: Eugeny A
authors.initials: EA
authors.lastname: Ermilov
authors.forename: Matthias
authors.initials: M
authors.lastname: Meyer
authors.forename: Norbert
authors.initials: N
authors.lastname: Jux
authors.forename: Andreas
authors.initials: A
authors.lastname: Hirsch
authors.forename: Beate
authors.initials: B
authors.lastname: Röder
mesh_terms: D040761:Biomimetic Materials / Q000737:chemistry; D002734:Chlorophyll / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry*; D016503:Drug Delivery Systems; D037741:Fullerenes / Q000737:chemistry*; D008958:Models, Molecular; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry; D013050:Spectrometry, Fluorescence
chemical_list: D037741:Fullerenes; D045322:Photosynthetic Reaction Center Complex Proteins; D002734:Chlorophyll; C040298:pyropheophorbide a; C069837:fullerene C60