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Electron Spin Exchange in Linked Phenothiazine–Viologen Charge Transfer Complexes Incorporated in “Through‐Ring” (Rotaxane) α ‐Cyclodextrins
Author(s) -
Yonemura Hiroaki,
Forbes Malcolm D. E.
Publication year - 2015
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/php.12436
Subject(s) - chemistry , acceptor , electron paramagnetic resonance , photochemistry , crystallography , moiety , rotaxane , electron transfer , photoinduced electron transfer , phenothiazine , electron donor , ring (chemistry) , excited state , stereochemistry , nuclear magnetic resonance , supramolecular chemistry , atomic physics , medicine , physics , organic chemistry , pharmacology , condensed matter physics , biochemistry , crystal structure , catalysis
A series of covalently bound phenothiazine ( PHZ ) donor and methylviologen (V) acceptor compounds with polymethylene chain spacers (C 8 , C 10 , C 12 ) were incorporated in a “through‐ring” (rotaxane) fashion to α ‐cyclodextrin ( α ‐ CD ) hosts such that the alkyl chains were fully extended, with the donor and acceptor on opposite sides of the α ‐ CD cylinder. Photoexcitation of the PHZ unit induces electron transfer from the PHZ first excited triplet state to the V moiety, forming a biradicaloid charge‐separated state. Time‐resolved electron paramagnetic resonance ( TREPR ) spectroscopy at the X‐band and Q‐band microwave frequencies was used to investigate the spin exchange interaction, J , in these biradicaloids. Simulation of the spectra using a “static” model for spin‐correlated radical pairs allows extraction of the J values, which are negative in sign and have absolute values range from 2 to 1000 Gauss. Comparison of the PHZ n V ( n  = 8, 10, 12) spectra to those obtained using phenyl ether spacers indicates that π ‐bonds may assist the electronic coupling. The results are discussed in terms of through‐bond vs through‐space electronic coupling mechanisms.

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