An Amorphous Polyurethane Exhibiting Colorless Transparency and Efficient Yellow Emission

A polyurethane soluble in organic solvents was synthesized via polyaddition of dicyclohexylmethane-4,4’-diisocyanate with a newly designed diol monomer containing 2-(3,5-dialkynyl-2-hydroxyphenyl)-5-tert-pentylbenzoxazole as an excited-state intramolecular proton transfer (ESIPT) luminophore. The resulting polyurethane is amorphous with a high glass transition temperature of 164 °C. Spin-coated thin films were colorless and transparent and exhibited efficient yellow emission with a fluorescence quantum yield of 0.46. The presence of two alkynyl groups and a tert-pentyl substituent on the benzoxazole-based ESIPT luminophore is key to the simultaneous realization of high solubility in organic solvents and the formation of colorless, transparent thin films exhibiting efficient visible-light emission.