Highly efficient and stable blue-light-emitting binaphthol-fluorene copolymers: A joint experimental and theoretical study of the main-chain chirality

Abstract

In a quest for the main-chain chiral and highly stable blue-light-emitting π-conjugated polymers, a novel series of soluble conjugated random and alternating copolymers (PF-BN) derived from fluorene and axially chiral 1,1'-binaphthol (BINOL) were successfully synthesized by Suzuki coupling polymerization. The polymer structures, optical properties, and their electrochemical properties were investigated by 1 H NMR, TGA/DSC, UV-Vis absorption, photoluminescence, cyclic voltammetry, circular dichroism spectroscopy, and DFT calculations. The blue-light-emitting BINOL-containing copolymers with proper content of BINOL show highly efficient photoluminescence and ultra highly stable light-emission with almost unchanged fluorescent spectra after annealing at 200 °C in air for 10 h. The joint experimental and theoretical study of the main-chain chirality reveals that (1) the chirality of BINOL can be transferred to the polymer backbone, (2) the effective conjugation length is about one BINOL and three fluorenes, (3) the main active chiral block in the copolymers is probably composed by one BINOL with the other two or three fluorenes, and (4) the dihedral angle in the PF-BN copolymers should be larger than 105°. The incorporation of BINOL into the polyfluorene backbone is an effective way to produce highly efficient and stable blue-light-emitting main-chain chiral conjugated polymer with interesting optoelectronic properties.