Photophysical properties of polyphenylphenyl compounds in aqueous solutions and application of their nanoparticles for nucleobase sensing

Abstract

Abnormal photoluminescent properties of polyphenylphenyl compounds 6,7-dicyano-2,3-di-[4-(2,3,4,5-tetraphenylphenyl)phenyl]quinoxaline (CPQ) and 6,7-dimethyl-2,3-di-(4-(2,3,4,5-tetraphenylphenyl)phenyl)quinoxaline (MPQ) in aqueous solutions have been investigated. Photoluminescent emissions of CPQ and MPQ in tetrahydrofuran (THF)–water mixtures do not change monotonously with increasing their effective concentration in solution. This phenomenon is different from both aggregation-induced emission quenching and aggregation-induced emission enhancement, and can be ascribed to the results of combinational effects of intramolecular rotation, intermolecular hydrogen bonds, and solvent viscosity and hydration. We also observed that organic nanoparticles of CPQ and MPQ are formed in the aqueous solutions. Based on detection of the fluorescence of CPQ nanoparticles in aqueous solutions when introducing nucleobases, we report for the first time the application of organic nanoparticles for nucleobase sensing and found that CPQ nanoparticles can recognize the nucleobases with a sensitivity of guanine > adenine > thymine ≥ cytosine. These findings elucidate the photoluminescent behavior of polyphenylphenyl compounds in aqueous solutions and provide an approach to apply fluorescent organic nanoparticles for biosensing instead of metal and inorganic nanoparticles.