Synthesis of regioregular pi-conjugated poly(thienyleneethynylene) with a hindered phenolic substituent

Pd-catalyzed C-C coupling reaction between an acetylenic compound and acryl halide provides a useful route for the preparation of poly(aryleneethynylene) (PAE) 3-substituted thiophene due to the difference in chemical reactivity between the 2- and 5- positions of 3-substituted regioregular PAE polymer. The CH3 signal of the t-Bu group appears as a singlet both in the H-nuclear magnetic resonance (NMR) and in the C{H}-NMR spectra which suggests free rotation of the hindered phenolic group on the NMR time scale. Lowering the temperature slows down the rotation, giving rise to several H-NMR peaks for the t-Bu protons at low temperature. Hindered phenolic group often generate a stable radical.