Unusual strong fluorescence of a hyperbranched phosphate: discovery and explanations

Abstract

The unusual strong fluorescence of a hyperbranched molecule (3-hydroxyphenyl) phosphate (HHPP), which does not possess a rigid planar structure or obvious large π system, was discovered for the first time. The effects of the solvent polarity, pH value, concentration, and end group modification on the absorption and the fluorescence spectra of HHPP solutions were investigated. The terminal phenol groups and triphenyl phosphate (TPP) structures in HHPP were found to be responsible for two strong fluorescence peaks. The greatly enhanced fluorescence is explained by three factors. In particular, the special bridging effects of the phosphate groups in the hyperbranched molecules, which can form extended π electron systems, play an important role. It is suggested that the phosphate groups in the hyperbranched molecule could serve as effective bridging groups to connect various other fluorescence groups to form a new type of fluorescence molecule which does not have a rigid planar structure. In addition, the systematic colour changes with changing solvent polarity, mass concentration, and pH value make it a new potential probe in various applications.