Exploring side-chain length effect on β-phase of polyfluorene derivatives in electrospinning and their optical behavior

Unique coplanar β-conformation of polyfluorene, endowed with long effective conjugated length, is promising to form ordered and oriented structures that can result in improved carrier mobility, polarization emission and excellent spectral stability. Herein, a series of polydiarylfluorenes of different side-chains (PHDPF, PODPF or PNDPF) and poly (9-vinylcarbazole) composite nanofibers were prepared via electrospinning approach. It is observed that β-phase can be obtained in PODPF electrospun nanofibers whereas absent in those of PHDPF and PNDPF systems. It can be demonstrated that the optimal chain length for polydiarylfluorenes to β-conformation is an octyl side chain in electrospinning. In contrast with the electrospun nanofibers, there was no β-phase in the corresponding spin-coated film. For the β-phase electrospun nanofibers, the fluorescence quenching sensitivity on 2, 4-dinitrotoluene (DNT) vapor was obviously higher than that of amorphous electrospun nanofibers and spin-coated film, respectively. Synergistic molecular design and electrospun processing may offer a fascinating strategy for the control of polymer conformation to the adjustment of nano and micro optical devices such as organic fluorescence sensors, lasers and light-emitting diodes.