Poly­(thiophene)­s have an inherently large third-order nonlinear optical (TONO) response, but applications are not straightforward due to unoptimized materials. Therefore, several structure–property relationships (molar mass, branching, regioregularity) are investigated to unravel which structural modifications give the highest TONO response. Poly­(3-hexylthiophene) with different molar masses, poly­[3-(2-ethylhexyl)­thiophene] with different molar masses, and random copolymers with different degrees of regioregularity are synthesized and measured by UV–vis spectroscopy and the third harmonic scattering technique. Every structural modification that leads to an increase in π–π interactions in poly­(thiophene)­s leads to an increase in the TONO response of the material. Therefore, a material with a high molar mass, an unbranched alkyl side chain, and a high regioregularity degree is preferably tested as a promising TONO material.

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The organizational behaviour of block copolymers consisting of two helical blocks with opposite chiral expression is investigated.