Synthesis and fluorescent properties of conjugated co-oligomers containing maleimide and carbazole units at the main chain

Abstract

Yamamoto coupling polymerizations of 2,3-diiodo-N-cyclohexylmaleimide (DICHMI) with dihalide carbazole derivatives (DXRCz) (3,6-dibromo-N-methylcarbazole (3,6-DBrMCz), 3,6-diiodo-N-hexylcarbazole (3,6-DIHCz) and 2,7-dibromo-N-hexylcarbazole (2,7-DBrHCz)) were performed using a nickel complex. The number-average molecular weights (Mn) of poly(N-cyclohexylmaleimide-co-N-substituted carbazole)s (poly(CHMI-co-RCz)) were in the range of 600–7300, as determined by gel permeation chromatography analyses. The fluorescence emissions of the poly(CHMI-co-RCz) solution showed two emission maxima in the 417–426 and 581–595 nm regions. The fluorescence peaks of co-oligomers at long wavelengths (581–595 nm) were attributable to the conjugated neighboring CHMI-RCz units of polymer main chains. The intensities of fluorescence emissions were significantly affected by the polarity of organic solvents such as tetrahydrofuran and N,N-dimethylformamide. The solvatochromic fluorescence phenomenon may be attributable to the twisting of CHMI-RCz bonds in an excited state in polar solvents. π-Conjugated polymers attract attention from showing not only an interesting electric and optical property but also workability. The random co-oligomers with N-cyclohexylmaleimide and N-substituted carbazole in the main chain were carried out by Yamamoto coupling reaction. The co-oligomers showed the fluorescence color of red from blue. Especially, when 2,7-dibromo-N-hexylcarbazole was used as the monomer, the fluorescence color of the resulting co-oligomer changed from magenta to blue by the difference of polarity of solvent.