Intrinsic Fluorescence Regulation of Aliphatic Hyperbranched Polyphosphate Esters via Steric Hindrance Reduction

Unconventional fluorescent polymers are attracting increasing attention due to their unique optical properties and broad application potential. To investigate their fluorescence behavior, a series of aliphatic hyperbranched polyphosphate esters exhibiting unconventional fluorescence were synthesized in this study. Experimental and theoretical calculation results revealed that inter/intramolecular hydrogen bonds facilitated molecular aggregation and enhanced the n-π interaction between oxygen and P═O groups. These reinforced n-π interactions promoted spatial electronic communication, thereby generating intrinsic fluorescence. Moreover, reducing the steric hindrance between functional groups may have enhanced the spatial electronic communication, which is likely associated with stronger fluorescence intensity and longer emission wavelengths. The obtained polymers were successfully applied in ion sensing and the fabrication of fluorescent hydrogels. Therefore, this work not only provides crucial insights into the origin of unconventional fluorescence but also offers an efficient strategy for developing high-performance unconventional fluorescent polymers.