BTDF shows a similar electronic structure to the PFBT polymer with the BT excitation and fluorene-related transition around 320 nm as well as a band from their interaction around 420 nm, both of these transitions are retained in the polymer but red-shifted due to the increased electron delocalization in the large conjugated system of the PFBT polymer (Figure ). In comparison to the PFBT polymer, the redox behaviour of BTDF is very clear with two reversible reductions at 1.89 and -2.49 V vs F c/F c + , and a linear scan rate dependence of the square root of the current as would be expected of a freely diffusing molecule. The two reversible reductions of BTDF are similar to that of the molecule BTDN (600 mV in between reductions as compared to 800 mV in BTDN) , however, shifted to more negative potentials due to the difference in electron richness between the side groups. The electrondonating dioctylfluorene units make the BT unit more difficult to be reduced as compared to the electron-withdrawing nitrile groups in BTDN .