Photophysical Investigationof Coumarin Solubilizationin Polyethylene Glycol Mediated by a 1,2,4-Triazolium Protic IonicLiquid

Abstract Polymers are remarkable macromolecules that can be fabricated with ease for the required potential applications, including biotechnology, medicine, engineering, and nanotechnology. Biocompatible and biodegradable polymers are now widely adopted in pharmaceutical formulations, since they offer better solubilization and enhanced bioavailability. One of the biggest challenges to pharmaceutical research is the poor aqueous solubility of hydrophobic drug molecules, which results in limited bioavailability and reduced therapeutic performance. In this work, well-established biocompatible polymer polyethylene glycol (PEG) is employed as the pharmaceutical excipient for the hydrophobic drug coumarin (COU). Along with PEG, a synthesized room-temperature triazolium-based protic ionic liquid (PIL) was incorporated as an additive, and their synergetic effect on COU solubilization was studied by exploring the photophysical properties of COU using steady-state and time-resolved fluorescence techniques. The experiments reveal that incorporation of COU into the PEG/IL system significantly alters the emission intensity, spectral position, and excited-state lifetime, indicating strong nanoenvironmental modulation. Quenching studies indicate the controlled accessibility of COU, suggesting that it is partially confined within PEG rather than entirely encapsulated. A 1,2,4-triazolium-based PIL/polymer platform enhances COU solubilization, where the polymer provides a confined environment for improved solubility and stability and the PIL enables fine control over local polarity, structural organization, and molecular accessibility. Overall, these results demonstrate that PEG/IL systems provide a versatile and reliable platform for enhancing the solubility, stability, and photophysical properties of hydrophobic drug molecules, which underscores their promise for advanced pharmaceutical formulations and sensing applications.