Effects of Chain Orientation and Packing on the Photoluminescence and Photothermal Properties of Polybenzimidazole Fibers with Meta-Linkage.

We herein report the influences of chain orientation and packing on the photoluminescent (PL) and photothermal properties of polybenzimidazole fibers with meta-linkage under different excitation wavelengths (λex) and powers of laser sources. For the purpose, poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole] (PmBI) was synthesized and then processed into fibers via solution spinning and heat treatment. The chain orientation and packing of the as-spun PmBI fiber decreased and increased owing to the heat treatment, respectively, which resulted from the nonlinear chain conformation of PmBI with meta-linkage. It was found that the visible PL intensity under λex = 325 nm, which is associated with an efficient interchain photorelaxation between benzimidazole rings, was much higher for the as-spun fiber with higher chain orientation, while the infrared PL intensity under λex = 514 nm, which is dominated by an intrachain photorelaxation, was far higher for the heat-treated fiber with higher chain packing. Accordingly, the heat-treated PmBI fiber exhibited excellent photothermal heating behavior by attaining maximum temperature increments (ΔTmax) of ~31.7 °C under λex = 405 nm and 18.4 mW, which was even higher than the as-spun fibers (ΔTmax ~ 27.5 °C). For the PmBI fibers, the ΔTmax values were also found to increase with the decrease of λex. [ABSTRACT FROM AUTHOR]