Optical corrective retardation films are widely used in the display industry to compensate for a variety of imperfections such as off-axis contrast reduction, grey-scale inversion and colour shifts in LCDs and backplane reflections in OLEDs. A wide variety of these films have been produced by multiple methods, however, obtaining ideal wavelength dispersion remains difficult and costly to achieve in thin, single-layer systems. In this work, we report the synthesis of a novel series of reactive mesogen materials designed to exhibit negative wavelength dispersion birefringence. This series of photopolymerisable materials based on a benzodithiophene core exhibiting either an ‘X’-shaped or ‘T’-shaped geometry were synthesised. Their negative wavelength dispersion birefringence properties were investigated in aligned films prepared from photo-polymerised reactive mesogen host mixtures. The nature of the substituents on the BDT core was found to have a significant impact on performance, and materials with an X-shaped geometry were found to exhibit much higher performance than those with a T-shape.