Fluorescence Quenching of CdSe Quantum Dots by Para-Substituted Anilines: An Undergraduate Exploration of Nanocrystal Surface Chemistry and Photodynamics

TCE

The Chemical Educator

ISSN: 1430-4171 (electronic version)

Table of Contents

Abstract Volume 25 (2020) pp 119-128

Fluorescence Quenching of CdSe Quantum Dots by Para-Substituted Anilines: An Undergraduate Exploration of Nanocrystal Surface Chemistry and Photodynamics

Mary E. Salyards and Martin R. McPhail*

Department of Chemistry, University of West Georgia, 1601 Maple Street, Carrollton, Georgia 30118, mmcphail@westga.edu
Received January 9, 2020. Accepted May 2, 2020.

Published: 1 June 2020

Abstract. Research into colloidal quantum dots (QDs) has been driven by their potential to couple light energy to the motion of electrons. Key photodynamics of these nanocrystals are often probed by tracking photoinduced charge transfer from the QD to an adsorbed molecular acceptor. While much of this work relies on ultrafast laser spectroscopy, simple measurements of fluorescence quenching of QDs in the presence of molecular charge acceptors can provide useful insight into the electronic and chemical interactions between quenchers and the nanocrystal surface. This report describes a three-week laboratory module for upper-level undergraduate students, where they compare the ability of different para-substituted anilines to quench the fluorescence of cadmium selenide QDs. CdSe QDs of various sizes are synthesized by the students and subsequently functionalized with quenchers. Photoluminescence intensity is measured as a function of the quencher:QD ratio to show that anilines with an electron-donating substituent are more effective at quenching QD fluorescence than anilines with an electron-withdrawing substituent. Students use a simple binding equilibrium to determine the average number and distribution of bound quenchers per QD and verify this binding by ¹H-NMR spectroscopy. Based on this data, students build a case that differences in quenching efficiency with QD size and quencher type are primarily caused by a change in the intrinsic rate of hole transfer rather than a change in the average number of bound quenchers per QD.

Key Words: Laboratories and Demonstrations; physical chemistry; surface chemistry; nanomaterials; quantum dots; fluorescence; charge transfer; upper-division undergraduate

(*) Corresponding author. (E-mail: mmcphail@westga.edu )

Article in PDF format (1040 KB) HTML format

Supporting Materials:

The supporting materials document contains handouts provided to students during each of the three weeks of the laboratory module. These handouts contain detailed background, procedures, example calculations, and discussion prompts pertaining to each week’s experiments. (1010 KB)