Synthesis and Spectroscopic and Electrochemical Characterisation of a Conducting Polythiophene Bearing a Chiral β-Substituent: Polymerisation of (+)-4,4′-Bis[(S)-2-methylbutylsulfanyl]-2,2′-bithiophene

A regioregular head-to-head/tail-to-tail poly(b,b'-disubstituted bithiophene) P1 was synthesised by chemical and electrochemical polymerisation of 2,2'-bithiophene that bears (S)-2-methylbutylsulfanyl chains in the b and b'-positions. The polymer was characterised by GPC, NMR and UV/Vis spectroscopy,CD, AFM and by electrochemical and conductivity measurements.The CD spectra of P1 in solutions in which poor solvents are present show interesting features and allow the presenceof different optically active species to be distinguished. Upon varying the casting conditions of P1, different relativeamounts of grainy and homogeneous aggregated phases were observed in AFM micrographies of films and correspondingnegative or positive first Cotton effects were found in the CD spectra. AFM, CD and UV/Vis characterisations were also performed on an electrogenerated optically active polymerPE1, in order to make a comparison with the chemically synthesised one. The interesting, small band gap of P1 allowsfor easy p- and n-electrochemical doping.