The photophysics of a 3-hydroxychromone dye, 2-(2-furyl)-3-hydroxychromone (FHC) was explored in different types of protic solvents by steady-state and time-resolved fluorescence spectroscopy. FHC exhibits a dual emission, attributable to the excited normal (N*) and tautomer (T*) forms resulting from an excited state intramolecular proton transfer (ESIPT) reaction (N*→T*). The ESIPT rate decreases with an increase in the hydrogen-bond donating ability of protic solvents. The proton-transfer dynamics is found to be unusually slow (∼10³ times slower than 3-hydroxyflavone) in strong hydrogen-bond donating solvents like methanol, trifluoroethanol or formamide, where it occurs on a time scale of ∼100–260 picoseconds. This slow dynamics is likely to be related to the intermolecular solvent–solute H-bonding interactions that compete with the intramolecular H-bond in FHC required for the ESIPT reaction. These data provide a physical background for recent applications of this dye as a fluorescence probe of the microenvironment in biomolecules.

Oral delivery of drugs is the most common method of drug administration. However, the poor bioavailability of drugs in the systemic circulation makes achieving therapeutic levels via the gastrointestinal (GI) tract challenging. Polymeric nanoparticle drug carriers can shield drugs from degradation and deliver them in the upper intestinal region of the GI tract. In this regard, we have developed a nanocarrier from a naturally occurring polymer, chitosan, to investigate its efficacy in a pH-responsive environment to be used as a potential drug delivery vehicle. We have monitored the encapsulation of an anti-tuberculosis drug, rifampicin (RF), to investigate its pH-responsive delivery activity. Although RF is poorly soluble in aqueous media, it is a clinically effective drug due to its ability to inhibit bacterial RNA polymerase. The inescapable necessity and poor solubility automatically necessitate an alternative drug delivery/carrier system. The chitosan nanoparticle system ensures a burst delivery efficiency of 75% of rifampicin at a simulated intestinal pH over a period of 24 hours. Our studies have successfully established the chitosan nanocarrier as a promising oral drug delivery vehicle.