Molecular Fluorescence

Principles and Applications

Bernard Valeur, Mário Nuno Berberan-Santos

• Publisher: Wiley-VCH
• Year: 2013
• Print ISBN: 9783527328468
• eBook ISBN: 9783527650026
• Edition: 2
• Topic: Physical Sciences
• Subtopic: Industrial & Technical Chemistry

Molecular Fluorescence

This second edition of the well-established bestseller is completely updated and revised with approximately 30 % additional material, including two new chapters on applications, which has seen the most significant developments.

The comprehensive overview written at an introductory level covers fundamental aspects, principles of instrumentation and practical applications, while providing many valuable tips.

For photochemists and photophysicists, physical chemists, molecular physicists, biophysicists, biochemists and biologists, lecturers and students of chemistry, physics, and biology.

1

Introduction

… ex arte calcinati, et illuminato aeri seu solis radiis, seu flammae fulgoribus expositi, lucem inde sine calore concipiunt in sese; …

[… properly calcinated, and illuminated either by sunlight or flames, they conceive light from themselves without heat; …]

Licetus, 1640 (about the Bologna stone)

1.1 What Is Luminescence?

The word luminescence, which comes from the Latin (lumen = light) was first introduced as luminescenz by the physicist and science historian Eilhardt Wiedemann in 1888, to describe “all those phenomena of light which are not solely conditioned by the rise in temperature,” as opposed to incandescence. Luminescence is often considered as cold light whereas incandescence is hot light.

Luminescence is more precisely defined as follows: spontaneous emission of radiation from an electronically excited species or from a vibrationally excited species not in thermal equilibrium with its environment.¹⁾ The various types of luminescence are classified according to the mode of excitation (see Table 1.1).

Table 1.1 The various types of luminescence.

Phenomenon	Mode of excitation
Photoluminescence (fluorescence, phosphorescence, delayed fluorescence)	Absorption of light (photons)
Radioluminescence	Ionizing radiation (X-rays, α, β, γ)
Cathodoluminescence	Cathode rays (electron beams)
Electroluminescence	Electric field
Thermoluminescence	Heating after prior storage of energy (e.g., radioactive irradiation)
Chemiluminescence	Chemical reaction (e.g., oxidation)
Bioluminescence	In vivo biochemical reaction
Triboluminescence	Frictional and electrostatic forces
Sonoluminescence	Ultrasound

Luminescent compounds can be of very different kinds:

• Organic compounds: aromatic hydrocarbons (naphthalene, anthracene, phenanthrene, pyrene, perylene, porphyrins, phtalocyanins, etc.) and derivatives, dyes (fluorescein, rhodamines, coumarins, oxazines), polyenes, diphenylpolyenes, some amino acids (tryptophan, tyrosine, phenylalanine), etc.
• Inorganic compounds: uranyl ion (
  
  ), lanthanide ions (e.g., Eu³⁺, Tb³⁺), doped glasses (e.g., with Nd, Mn, Ce, Sn, Cu, Ag), crystals (ZnS, CdS, ZnSe, CdSe, GaS, GaP, Al₂O₃/Cr³⁺ (ruby)), semiconductor nanocrystals (e.g., CdSe), metal clusters, carbon nanotubes and some fullerenes, etc.
• Organometallic compounds: porphyrin metal complexes, ruthenium complexes (e.g.,
  
  ), copper complexes, complexes with lanthanide ions, com­plexes with fluorogenic chelating agents (e.g., 8-hydroxy-quinoline, also called oxine), etc.

Fluorescence and phosphorescence are particular cases of luminescence (Table 1.1). The mode of excitation is absorption of one or more photons, which brings the absorbing species into an electronic excited state. The spontaneous emission of photons accompanying de-excitation is then called photoluminescence which is one of the possible physical effects resulting from interaction of light with matter, as shown in Figure 1.1. Stimulated emission of photons can also occur under certain conditions (see Chapter 3, Box 3.2). Additional processes, not shown, can take place for extremely high intensities of radiation, but are not relevant for luminescence studies.

Figure 1.1 Position of photoluminescence in the frame of light–matter interactions.

1.2 A Brief History of Fluorescence and Phosphorescence

It is worth giving a brief account of the history of fluorescence and phosphorescence. The major events from the early stages to the middle of the twentieth century are reported in Table 1.2 together with the names of the associated scientists. The story of fluorescence started with a report by N. Monardes in 1565, but scientists focused their attention on light emission phenomena other than incandescence only in the nineteenth century. However, the major experimental and theoretical aspects of fluorescence and phosphorescence were really understood only after the emergence of quantum theory, already in the twentieth century (1918–1935, i.e., less than 20 years). As in many other areas of theoretical physics and chemistry, this was an exceptionally fecund period.

Table 1.2 Milestones in the history of fluorescence and phosphorescence^a).

Year	Scientist	Observation or achievement
1565	N. Monardes	Emission of light by an infusion of the wood later called Lignum nephriticum (first report on the observation of fluorescence)
1602	V. Cascariolo	Emission of light by Bolognese stone (first detailed observation of phosphorescence)
1640	Licetus	Study of Bolognian stone. First definition as a nonthermal light emission
1833	D. Brewster	Emission of light by chlorophyll solutions and fluorspar crystals
1842	J. Herschel	Emission of light by quinine sulfate solutions (epipolic dispersion)
1845	E. Becquerel	Emission of light by calcium sulfide upon excitation in the UV
		First statement that the emitted light is of longer wavelength than the incident light.
1852	G. G. Stokes	Emission of light by quinine sulfate solutions upon excitation in the UV (refrangibility of light)
1853	G. G. Stokes	Introduction of the term fluorescence
1858	E. Becquerel	First phosphoroscope. First lifetime measurements.
1867	F. Goppelsröder	First fluorometric analysis (determination of Al(III) by the fluorescence of its morin chelate)
1871	A. Von Baeyer	Synthesis of fluorescein
1888	E. Wiedemann	Introduction of the term luminescence
1905, 1910	E. L. Nichols and E. Merrit	First fluorescence excitation spectrum of a dye
1907	E.L. Nichols and E. Merrit	Mirror symmetry between absorption and fluorescence spectra
1919	O. Stern and M. Volmer	Relation for fluorescence quenching
1920	F. Weigert	Discovery of the polarization of the fluorescence emitted by dye solutions
1922	S. I. Vavilov	Excitation-wavelength independence of the fluorescence quantum yield
1923	S. I. Vavilov and W. L. Levshin	First study of the fluorescence polarization of dye solutions
1924	S. I. Vavilov	First determination of fluorescence yield of dye solutions
1924	F. Perrin	Quantitative description of static quenching (active sphere model
1924	F. Perrin	First observation of alpha phosphorescence (E-type delayed fluorescence)
1925	F. Perrin	Theory of fluorescence polarization (influence of viscosity)
1925	W. L. Levshin	Theory of polarized fluorescence and phosphorescence
1925	J. Perrin	Introduction of the term delayed fluorescence
		Prediction of long-range energy transfer
1926	E. Gaviola	First direct measurement of nanosecond lifetimes by phase fluorometry (instrument built in Pringsheim’s laboratory)
1926	F. Perrin	Theory of fluorescence polarization (sphere)
		Perrin’s equation
		Indirect determination of lifetimes in solution.
		Comparison with radiative lifetimes
1927	E. Gaviola and P. Pringsheim	Demonstration of resonance energy transfer in solutions...

Table of contents

• Cover
• Further Titles of Interest
• Title page
• Copyright page
• Preface to the First Edition
• Preface to the Second Edition
• Acknowledgments
• Prologue
• 1 Introduction
• Part I: Principles
• Part II: Techniques
• Part III: Applications
• Appendix: Characteristics of Fluorescent Organic Compounds
• Epilogue
• Index