Concentration-induced discoloration properties of poly(alkoxynaphthalene)s synthesized by solid-state oxidative coupling polymerization

Abstract

Poly(alkoxynaphthalene)s were synthesized by grinding 2-alkoxynaphthalenes with FeCl3 as the oxidant at room temperature via solid-state oxidative coupling polymerization. Based on the structural characterization and analysis, the condensed structure of 1,4-linked polynaphthalenes is the dominant structure of the polymer, accompanied with the formation of intramolecular coupling. The polymers not only exhibit perfect heat-resistant property, but also show the concentration-induced discoloration property. With the continuously increasing polymer concentrations, the maximum fluorescence bands were observed from the ultraviolet region to 520nm, eventually red shifting to 620nm at the polymer concentration above 0.1mgmL−1. Moreover, the choice of solvent and the extended side-chains can affect the fluorescence spectral changes. In combination with the fluorescence spectral changes of poly(alkoxynaphthalene)s in PMMA films, the concentration-induced discoloration property is mainly dependent on a transition from twisted conformations to planar structures and the formation of polymer aggregates. Moreover, these polymers exhibit obvious enhanced emissions and on/off fluorescent switching which sense THF vapor. It is suggested that poly(alkoxynaphthalene)s are potential materials for fabrication of fluorescence sensors to detect THF efficiently.