Remarkably <i>Stretched Cis–Transoid</i> Helices Generated in Solid Phase and Solution of Poly(carbazole acetylene) Prepared Using an Organorhodium Catalyst in Toluene

Abstract

A helical π-conjugated poly­(<i>N</i>-isobutyl-3-carbazole acetylene), P­(<i>i</i>BCzA) was stereoregularly prepared using an [Rh­(norbornadine)­Cl]₂–triethylamine catalyst in toluene at 25 °C to determine the detailed geometrical and spatial structures in a tetrahydrofuran (THF) solution and the solid phase. P­(<i>i</i>BCzA), which has a bright orange color, was obtained in a yield of 90%. The 2D NMR spectrum of P­(<i>i</i>BCzA) in THF-<i>d</i>₈ at 50 °C indicated that an extraordinarily extended helix was produced. The WAXS pattern of P­(<i>i</i>BCzA) showed the formation of a tetragonal crystal packed with a remarkably <i>stretched cis–transoid</i> (REST^CT) helix similar to that observed in the solution state. This REST^CT helix was confirmed not to be an energetically stable but a metastable structure using MMFF94 program. The solid phase UV–vis spectrum of P­(<i>i</i>BCzA) showed the formation of a radical cation called a polaron because of the very large red shifts compared to that observed in solution without the doping