Structural, photophysical, and conductive properties of n-hexyl substituted hybrid polysilylene-polysilyne networks

Structural, photophysical, and charge transport properties of n-hexyl substituted polysilylenes containing 5, 33 or 67% n-hexylsilyne branching points were investigated. According to WAXD, DSC, and vibrational studies, introduction of branching points partially reduces the high degree of crystallinity of linear poly(di-n-hexylsilylene). A thermal transition occurs in all polymers, which leads to solid state thermochromic behavior. Solution thermochromism is also observed. It is shown that in the partially branched polymers the narrow band gap of polysilynes is accompanied by an exciton delocalization approaching that of linear polysilylenes. In the solid state, charge carrier mobilities, determined with the pulse-radiolysis time-resolved microwave conductivity technique, are high but decrease with increasing branching. They range from 1.5 x 10(-5) for the linear polymer to 7.6 x 10(-7) m(2) V-1 s(-1) for the polymer with 67% branching sites. At the thermal transition an abrupt drop in the mobility is observed, of which the magnitude decreases with increasing branching. The branching points appear to act as scattering points for both exciton and charge carrier migration.