In order to tune the optical properties of poly(3-alkylthiophene)s, varying amounts of phenyl groups were incorporated more or less randomly along the backbone of this polymer. Because a living random copolymerization of thiophene and phenyl monomers is not possible in standard conditions, a specially designed biaryl monomer was used. The degree of randomness of this incorporation could be estimated by an in-depth H-1 NMR analysis. The effect on the bandgap was remarkable, since a linear relation between the bandgap and the percentage of introduced phenyl rings was observed. This enables the synthesis of conjugated polymers with tunable and predictable bandgaps. Aggregation and crystallization behavior were also affected by the introduction of phenyl rings. Aggregation was still possible with 20% of phenyl rings, albeit to a small extent, while crystallization was already completely inhibited at that point.