Premium
Dendritic Porphyrin–Fullerene Conjugates: Efficient Light‐Harvesting and Charge‐Transfer Events
Author(s) -
Schlundt Sebastian,
Kuzmanich Gregory,
Spänig Fabian,
de Miguel Rojas Gustavo,
Kovacs Christian,
GarciaGaribay Miguel A.,
Guldi Dirk. M.,
Hirsch Andreas
Publication year - 2009
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200902161
Subject(s) - intramolecular force , photochemistry , chemistry , porphyrin , ultrafast laser spectroscopy , conjugate , singlet state , benzonitrile , excited state , stereochemistry , spectroscopy , mathematical analysis , physics , mathematics , quantum mechanics , medicinal chemistry , nuclear physics
A novel dendritic C 60 ‐H 2 P‐(ZnP) 3 (P=porphyrin) conjugate gives rise to the successful mimicry of the primary events in photosynthesis, that is, light harvesting, unidirectional energy transfer, charge transfer, and charge‐shift reactions. Owing, however, to the flexibility of the linkers that connect the C 60 , H 2 P, and ZnP units, the outcome depends strongly on the rigidity/viscosity of the environment. In an agar matrix or Triton X‐100, time‐resolved transient absorption spectroscopic analysis and fluorescence‐lifetime measurements confirm the following sequence. Initially, light harvesting is seen by the peripheral C 60 ‐H 2 P‐ *(ZnP) 3 conjugate. Once photoexcited, a unidirectional energy transfer funnels the singlet excited‐state energy to H 2 P to form C 60 ‐*(H 2 P)‐(ZnP) 3 , which powers an intramolecular charge transfer that oxidizes the photoexcited H 2 P and reduces the adjacent C 60 species. In the correspondingly formed (C 60 ) .− ‐(H 2 P) .+ ‐(ZnP) 3 conjugate, an intramolecular charge‐shift reaction generates (C 60 ) .− ‐H 2 P‐(ZnP) 3 .+ , in which the radical cation resides on one of the three ZnP moieties, and for which lifetimes of up to 460 ns are found. On the other hand, investigations in organic media (i.e., toluene, THF, and benzonitrile) reveal a short cut, that is, the peripheral ZnP unit reacts directly with C 60 to form (C 60 ) .− ‐H 2 P‐(ZnP) 3 .+ . Substantial configurational rearrangements— placing ZnP and C 60 in proximity to each other—are, however, necessary to ensure the required through space interactions (i.e., close approach). Consequently, the lifetime of (C 60 ) .− ‐H 2 P‐(ZnP) 3 .+ is as short as 100 ps in benzonitrile.