The Aggregation and Disaggregation Behavior of Chain Aromatic Hydrocarbon Derivatives Modulated by pH and act as Efficient Fluorescence Quencher for Polycyclic Aromatic Hydrocarbons.

Abstract

In this work, two chain aromatic hydrocarbon derivatives 1-2, which are constructed by linking two 3 H-imidazo[4,5-b]pyridine moieties through phenyls and oxygen bridges, were designed and synthesized. The aggregation and disaggregation behavior of these sensors could be modulated by pH, as evidenced by H¹ NMR, fluorescence spectrum and DLS, attributable to the altered deprotonation of the 3 H-imidazo[4,5-b]pyridine cores. An increase in the sensor concentration leads to the reemergence of aggregation, correspondingly diminishing the fluorescence intensity. Polyaromatic aromatic hydrocarbons (PAHs), known for their luminescent characteristics, demonstrate sustained luminescence even at high concentrations of 10^- 3 M. Notably, the fluorescence of PAHs are effectively quenched upon mixed with 7 × 10^- 5 M aggregated sensor 1 or 10^- 4 M aggregated sensor 2. Aggregation is identified as the predominant mechanism for fluorescence quenching, the finding corroborated by fluorescence spectroscopy and DLS measurements. Based on computational studies and mechanistic evaluations, sensors 1 and 2 emerge as promising candidates for serving as efficient fluorescence quenchers for polycyclic aromatic hydrocarbons.