Using Luminescence To Show Intramolecular and Intermolecular Hydrogen Bonding: An Activity for General Chemistry or Physical Chemistry

Abstract

A hands-on activity for students in general chemistry and physical chemistry courses has been designed to facilitate study of intramolecular (IntraHB) and intermolecular (InterHB) hydrogen bonding in biomolecules using luminescence. 3-Hydroxyflavone (3-HF), the backbone of all flavonols, is a promising model molecule, for it possesses an excited-state intramolecular proton transfer (ESIPT) effect that can serve as a fluorescent probe for studying many biological systems. The luminescence of 3-HF has one or two bands, whose intensities are dependent on temperature and solvent. In this activity, molecular models are used to illustrate hydrogen bonding of 3-HF in the ground state in two solvents, ethanol and hexane. Then students perform an activity to enable them to observe the luminescence of 3-HF in ethanol and in hexane, at room temperature and at 77 K, respectively, followed by discussion of the luminescence of 3-HF in ordinary filter paper. The project allows students to relate the idea of hydrogen bon...