Effects of mono-substituents on the polarity-sensitive fluorescent probe properties of pyrene

This study investigates the effects of mono-substituents (i.e., hydroxyl, methyl, amino and nitro groups) on the polarity-sensitive fluorescent probe properties of pyrene (Pyr) using fluorescence, UV–vis, and circular dichroism absorption spectroscopy. The results indicate that the four mono-substituents altered the fluorescence spectral characteristics of Pyr to varying degrees, with the most to least influential order being: nitro, amino, hydroxyl, and methyl. 1-Aminopyrene (1-APyr) and 1-nitropyrene (1-NPyr) are deemed unsuitable for use as polarity-sensitive fluorescent probes due to their limited or absent spectral characteristics. The I 386 /I 406 and I 376 /I 396 ratios of 1-HPyr and 1-MPyr decrease as solvents polarity increases, contrasting with the I 372 /I 384 ratio of Pyr. Thus, 1-hydroxypyrene (1-HPyr) and 1-methylpyrene (1-MPyr) also exhibit polarity-sensitive characteristics similar to Pyr, and their solubility in PBS buffer surpasses that of Pyr at 298 K. Moreover, 1-HPyr and 1-MPyr are practicable for detecting the polarity of human serum albumin (HSA) under simulated physiological conditions. The results underscore the potential of the polarity-sensitive mono-substituents of Pyr in biological applications, particularly in probing protein polarity and conformational changes, and further providing a potential tool for the related research in biochemistry and pathology.