title: Chain folding controlled by an isomeric repeat unit: helix formation versus random aggregation in acetylene-bridged carbazole-bipyridine co-oligomers.
abstract: An unprecedented, positional effect of the isomeric repeat unit on chain folding in donor–acceptor-linked oligomers, which contain alternating bipyridine and carbazole moieties that are connected through an acetylinic linkage, is reported. 4,4′-Linked oligomer 1 adopts an intrachain helical conformation (CD-active) in CHCl3/MeCN (20:80 v/v), whereas oligomer 2, which contains an isomeric 6,6′-linkage, forms interchain randomly coiled aggregates (CD-inactive). The substitution position plays a significant role in controlling the variations in electronic effects and dipole moments around the bipyridyl moiety, which are responsible for this observed phenomenon. Two model compounds of oligomers 1 and 2 (3 and 4, respectively) were prepared and their properties were compared. A systematic investigation of the photophysical and CD properties of these structures, as well as theoretical studies, support our conclusions.
authors: Photosciences and Photonics Group, Chemical Sciences and Technology Division, CSIR-National Institute for Interdisciplinary Science and Technology (CSIR-NIIST), Trivandrum-695 019, Kerala, India.
authors: Kizhmuri P
authors: KP
authors: Divya
authors: Sivaramapanicker
authors: S
authors: Sreejith
authors: Cherumuttathu H
authors: CH
authors: Suresh
authors: Divya S
authors: DS
authors: Philips
authors: Ayyappanpillai
authors: A
authors: Ajayaghosh
mesh_terms: D000114:Acetylene / Q000737:chemistry*; D002227:Carbazoles / Q000737:chemistry*; D002942:Circular Dichroism; D007536:Isomerism; D011108:Polymers / Q000138:chemical synthesis / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry
chemical_list: D002227:Carbazoles; D011108:Polymers; D011725:Pyridines; D012997:Solvents; C041514:carbazole; C023666:pyridine; D000114:Acetylene