Fluorescence

This chapter surveys some of the main capabilities, techniques, and measurements that are enabled by fluorescence. It covers spectra, quantum yield, lifetime, quenching, anisotropy, and microscopy, in each case citing topical review articles, many of the original references, underlying theory and modern day applications. Measuring absorption and fluorescence spectra is usually the first place to start in any fluorescence study. In order to illustrate how absorption and fluorescence spectra often interplay in tandem, the chapter considers the example of the auto-oxidation of 3,4-dihydroxy-l-phenylalanine (l-DOPA) to produce melanin. Lifetime measurement has emerged in recent years as the most powerful and versatile technique in fluorescence spectroscopy. The basis of fluorescence anisotropy techniques is to use polarized excitation to create a spatially selected, non-random, distribution of excited fluorescent molecules which then randomize, most commonly by Brownian rotation, but also at times by energy migration depending on the system.