Thermally removable sidechain stabilized benzodipyrrole as an electron-rich building block used in donor–acceptor conjugated polymers†

Abstract

Developing new structures of conjugated polymers is an important way of exploring the potential of polymeric electronic materials and improving the performance of the corresponding devices. In this work, we present an electron-rich building block, BDPBoc, based on benzodipyrrole with a removable side chain of t-butyloxycarbonyl (Boc) for donor–acceptor conjugated polymers to modulate their energy levels. After polymerization with widely used acceptor fragments of IID, BDOPV, and F₄BDOPV, Boc groups can be easily removed by thermal treatment at 240 °C, yielding BDP-based conjugated polymers. The BDP donor fragment exhibits an extremely electron-rich nature, bearing a HOMO energy level of −4.86 eV, which causes BDP-based polymers to have high HOMO level and local intrachain orbital distributions, resulting in lower polymer bandgaps and tight interchain packing. IID-BDP, BDOPV-BDP and F₄BDOPV-BDP polymers showed well-ordered solid-state structures and excellent charge transporting performances, where F₄BDOPV-BDP exhibited electron mobilities up to 0.20 cm² V⁻¹ s⁻¹ and conductivities up to 0.04 S cm⁻¹ after doping. Furthermore, the BDP-based polymer films spontaneously become porous during the deprotection of the Boc groups, suggesting their potential as thermoelectric and capacitor materials.