Premium
Precise Control of Intramolecular Charge‐Transport: The Interplay of Distance and Conformational Effects
Author(s) -
Schubert Christina,
Wielopolski Mateusz,
Mewes LarsHendrik,
de Miguel Rojas Gustavo,
van der Pol Cornelia,
Moss Kathryn C.,
Bryce Martin R.,
Moser Jacques E.,
Clark Timothy,
Guldi Dirk M.
Publication year - 2013
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.201204055
Subject(s) - intramolecular force , chemistry , photochemistry , moiety , ultrafast laser spectroscopy , conjugated system , radical ion , acceptor , electron transfer , photoexcitation , electron acceptor , crystallography , stereochemistry , ion , spectroscopy , excited state , polymer , atomic physics , organic chemistry , physics , quantum mechanics , condensed matter physics
A new series of donor–bridge–acceptor (D–B–A) compounds consisting of π‐conjugated oligofluorene (oFL) bridges between a ferrocene (Fc) electron‐donor and a fullerene (C 60 ) electron‐acceptor have been synthesized. In addition to varying the length of the bridge (i.e., mono‐ and bi‐fluorene derivatives), four different ways of linking ferrocene to the bridge have been examined. The Fc moiety is linked to oFL: 1) directly without any spacer, 2) by an ethynyl linkage, 3) by a vinylene linkage, and 4) by a p ‐phenylene unit. The electronic interactions between the electroactive species have been characterized by cyclic voltammetry, absorption, fluorescence, and transient absorption spectroscopy in combination with quantum chemical calculations. The calculations reveal exceptionally close energy‐matching between the Fc and the oFL units, which results in strong electronic‐coupling. Hence, intramolecular charge‐transfer may easily occur upon exciting either the oFLs or Fcs. Photoexcitation of Fc–oFL–C 60 conjugates results in transient radical‐ion‐pair states. The mode of linkage of the Fc and FL bridge has a profound effect on the photophysical properties. Whereas intramolecular charge‐separation is found to occur rather independently of the distance, the linker between Fc and oFL acts (at least in oFL) as a bottleneck and significantly impacts the intramolecular charge‐separation rates, resulting in beta values between β CS 0.08 and 0.19 Å −1 . In contrast, charge recombination depends strongly on the electron‐donor–acceptor distance, but not at all on the linker. A value of β CR (0.35±0.01 Å −1 ) was found for all the systems studied. Oligofluorenes prove, therefore, to be excellent bridges for probing how small structural variations affect charge transport in D–B–A systems.