We have examined the microstructure, solution processing, thermal transitions, and
mechanical properties of regioregular poly(nonylbithiazole) (PNBT). PNBT can adopt three distinct colors
in the solid stateyellow, red, and metallic greendepending on processing conditions such as polymer
concentration, solvent evaporation rate, temperature, and pressure. Microstructural variations were
observed between samples of different colors, including the intensification of optical absorption with the
degree of crystalline order and/or crystal size. Yellow samples lacked well-developed three-dimensional
order, whereas red and green samples were semicrystalline. The development of a lyotropic mesophase
was observed at intermediate concentrations in a “diffusion couple” geometry. A crystal model with two
planar, π-stacked chains per unit cell was shown to be consistent with the experimental diffraction data.
The simulated orthorhombic unit cell parameters are a = 2.38 nm, b = 0.72 nm, and c = 0.79 nm.