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Metal‐Induced Supramolecular Chirality in an Optically Active Polythiophene Aggregate
Author(s) -
Goto Hidetoshi,
Okamoto Yoshio,
Yashima Eiji
Publication year - 2002
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 - 10.1002/1521-3765(20020902)8:17<4027::aid-chem4027>3.0.co;2-q
Subject(s) - chirality (physics) , circular dichroism , cotton effect , polythiophene , supramolecular chirality , zinc , chemistry , crystallography , metal , supramolecular chemistry , thiophene , polymer chemistry , photochemistry , materials science , polymer , organic chemistry , conductive polymer , crystal structure , physics , chiral symmetry breaking , quantum mechanics , nambu–jona lasinio model , quark
Chiral polythiophenes (PTs), in sharp contrast to other optically active polymers, exhibit optical activity in the π–π* transition region which is derived from the chirality of the main chain when they self‐assemble to form a supramolecular π‐stacked aggregate with intermolecular interactions in a poor solvent or in a film. We now report that the regioregular, optically active PT poly[( R )‐3‐{4‐(4‐ethyl‐2‐oxazolin‐2‐yl)phenyl}thiophene] (poly‐ 1 ) exhibits unique split‐type induced circular dichroism (ICD) in the π–π* transition region of the main chain upon complexation with various metal salts such as trifluoromethanesulfonates of copper( I ), copper( II ), silver( I ), and zinc( II ), and iron( II ) perchlorate in chloroform, which is a good solvent for poly‐ 1 . The appearance of ICD and slight changes in the UV/Vis spectra (no color change), except for the zinc salts, indicated that the chirality may not be induced by chiral π‐stacked aggregates of poly‐ 1 , but by the chirality of the main chain, for example, a predominantly one‐handed helical structure induced by intermolecular coordination of the oxazoline groups to metal ions. The sign of the Cotton effect depends on the metal salt; most metal salts induced ICDs with similar Cotton‐effect patterns, while zinc salts caused an inversion of the signs of the Cotton effect of poly‐ 1 accompanied by a gradual red shift in the absorption of up to 125 nm. The changes in the conformation and the size of the poly‐ 1 aggregates induced by different metal salts were also investigated by 1 H NMR titrations, static light scattering (SLS), atomic force microscopy (AFM), and membrane filtration. On the basis of these results, we propose a possible model for the chiral supramolecular aggregates of poly‐ 1 with metal salts.