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Controlling Conformations in Alternating Dialkylsilylene‐Spaced Donor–Acceptor Copolymers by a Cooperative Thorpe–Ingold Effect and Polymer Folding
Author(s) -
Chen ChihHsien,
Huang YenChin,
Liao WeiChih,
Lim TsongShin,
Liu KuanLin,
Chen IChia,
Luh TienYau
Publication year - 2012
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.201102032
Subject(s) - chromophore , acceptor , chemistry , moiety , copolymer , photochemistry , folding (dsp implementation) , polymer , crystallography , stereochemistry , organic chemistry , physics , condensed matter physics , engineering , electrical engineering
Abstract A series of dialkylsilylene‐spaced copolymers 6 and 7 , which contain Me 2 Si and i Pr 2 Si spacer groups, respectively, and have alternating donor and acceptor chromophores, have been designed and regioselectively synthesized by hydrosilylation. The ratio of the donor and acceptor chromophores for each repeat unit is 2:1, and the two donor chromophores are linked by a trimethylene bridge. A 4‐aminostyrene moiety is used as the donor and a series of acceptor chromophores with different reduction potentials are employed. Both steady‐state and kinetic measurements reveal that the photoinduced electron transfer (PET) in 6 obeyed the Marcus theory in which normal and inverted regions are observed. On the other hand, the i Pr 2 Si‐spaced copolymers 7 exhibit absorption and emission from the charge‐transfer complexes exclusively due to ground‐state interactions between the donor and acceptor chromophores. The discrepancy in photophysical behavior may have arisen from the difference in distance between the adjacent donor and acceptor chromophores. The bulkiness of the substituents on the silicon atom (i.e., Me versus i Pr) may exert the Thorpe–Ingold effect on the local conformation around the silicon atom. The differences in the small energetic barriers for each of the conformational states may be amplified by extending the distance of the folding structure, which results in perturbing the conformation of the polymers. These results suggest that the electronic interactions between adjacent donor–acceptor pairs in these copolymers are controlled by the synchronization of the substitution effect and corresponding polymeric structures.