Stokes formed the solar spectrum by means of a prism. When he moved the solution of quinine through the visible part of the spectrum, there was

Paper No. : 06 Atomic Spectroscopy Module :08 History of Fluorescence

Principal Investigator: Dr.NutanKaushik, Senior Fellow

The Energy and Resouurces Institute (TERI), New Delhi Co-Principal Investigator: Dr. Mohammad Amir, Professor of Pharm. Chemistry,

JamiaHamdard University, New Delhi

Paper Coordinator: Dr. MymoonaAkhtar, Associate professor, Dept. of Pharm.

Chemistry, JamiaHamdard, New Delhi.

Content Writer: Dr. MymoonaAkhtar, Associate professor, Dept. of Pharm.

Description of Module

Subject Name Analytical Chemistry / Instrumentation Paper Name Atomic Spectroscopy

Module Name/Title History of Fluorescence

Module Id 08

Pre-requisites

Objectives Basic concept

Various phases in the discovery of fluorescence

Early observation of the phenomena and its understanding The discovery of fluorescent compounds

Some milestones in discovery of fluorescent compounds.

Early applications and Instrumentation

Keywords Photoluminescence, History, fluorescence, Stokes, L. nephriticum

Introduction

Photoluminescence, is a phenomenon of emission of light from excited electronic states after the species has absorbed light of definite wavelength. The field of photoluminescence has become an important tool in many scientific and technological fields, like biology, chemistry, physics, materials science and even medicine. Photoluminescence makes basis of many important applications such as fluorescent tubes, plasma screens, fluorescence microscopy and lamps, optical brighteners, fluorescent and phosphorescent paints, forensics, tracers in hydrogeology, phosphorescent labels, safety signs, and counterfeit detection in bank notes, security documents, art works,

Luminescence is different from incandescence and can be distinguished from it, as incandescence is light emitted by bodies heated at high temperatures.

The term luminescence has Latin root and comes from the word “lumen” which means light. German physicist and science historian Eilhard Wiedemann was the first person to introduced luminescence in 1888 for all other phenomena of light that do not result by the rise in temperature like incandescence.

Fluorescence, phosphorescence, and delayed fluorescence are well-known forms of photoluminescence. Other types of luminescence known are

 bioluminescence,

 chemiluminescence,

 cathodoluminescence,

 electroluminescence,

 radioluminescence,

 thermoluminescence,

 sonoluminescence,

 triboluminescence

Figure 1: Simplified way of Perrin-Jablonski diagram showing the phenomena of fluorescence and phosphorescence and difference between them

When a molecule losses its extra energy absorbed in the form of radiation from the first excited singlet state S1 the phenomenon is called fluorescence whereas when the emission takes place from the triplet state T1 after intersystem crossing from S1 the phenomenon is called phosphorescence. The term fluorescence was first coined by scientist G. G. Stokes in the middle of the 19th century. The distinction between fluorescence and phosphorescence was based on the duration of emission after the end of excitation. An emission of light that stops/disappears simultaneously with the end of excitation is known as fluorescence, whereas the phosphorescence is the emitted light that persists even after the end of excitation. But such a criterion is insufficient because there are long-lived fluorescence (e.g., divalent europium salts) and short-lived phosphorescence (e.g., violet luminescence of zinc sulfide) whose durations are comparable (several hundreds of nanoseconds).

The usual condition for an emission to be considered as phosphorescence is that the excited species must pass through an intermediate state i.e. form singlet to triplet state before emission. This observation was made and as stated for the first time in 1929 by Francis Perrin. More precisely, in the frame of molecular photochemistry, it is now said that the phosphorescence involves change in spin multiplicity i.e. from singlet to triplet or vice versa, where as the in the case of fluorescence spin multiplicity is retained . Discovery and early observation of the phenomena and its understanding

In Middle Ages, the term phosphor was therefore used to designate materials that glow/radiate light in the dark after being exposed to light. Many ancient reports can be found related to glow-in- the- dark minerals, and Bolognian phosphor (impure barium sulfide) is the most famous of them. It was discovered in 1602 by a cobbler from Bologna, Vincenzo Cascariolo.

Nicolas Monardes (1565) a Spanish physician and botanist, under certain conditions of observation reported the peculiar blue color from an infusion of a wood from Mexico and used to treat urinary and kidney diseases.

Monardes work was translated in 1574 by Charles de L’Écluse a Flemish botanist. He proposed Lignum Nephriticum (kidney wood) name to the wood used by Monrade to obtain the extract. This extended awareness of its strange optical properties in Europe. Because of the medicinal virtues of this wood for treating kidney ailments, it was very popular in XVI - XVII Europe. Around the same time, a Franciscan missionary, Bernardino de Sahagún (1499- 1590), independently described the wood– called “coatli” by the Aztecs in the Florentine Codex.

Source: Sahagún, Florentine Codex Vol. III f. 266; CM-RAH, f. 203v Coatli ...patli, yoanaqujxtiloni, matlaticiniayoaxixpatli..

“it is a medicine, and makes the water of blue color, its juice is medicinal for the urine

(A) (B)

A) Absorption and fluorescence colors of infusions of L. nephriticum in daylight.B) mildly alkaline aqueous solution to which chips of Eysenhardtiapolystachia were added. (source: J. Chem. Educ. 2011, 88, 731–738)

Structure of tetrahydromethanobenzofuro[2,3-d]oxacine, which is responsible for the fluorescence of L. nephriticum.

In 1603 a Bolognian shoemaker Vincenzo Casciarolo, discovered that a stone, emitted purple-blue light in the dark after being baked.

The stone was named as lapis solaris, which was later probably, identifies as barium sulfate. The discovery started a lively debate among the scientific community at the time.

In 1612 Galileo Galilei described the emission of light (phosphorescence) from the famous Bolognian stone his concern was that “It must be explained how it happens that the light is conceived into the stone, and is given back after some time.”

This system was investigated fully in 1664 by Robert Boyle after being inspired by Monardes’ report. His observation was that the wood loses its power to give color to the water after many infusions. He concluded that there was some “essential salt” in the wood responsible for the effect. He also discovered colour change with change in pH. He discovered that addition of acid abolished the color and that addition of alkali brought it back.

In 1833 Sir David Brewster, a Scottish physicist reported in his article “ On the Colour of Natural Bodies” the discovery of red fluorescence of chlorophyll. He described in his article that when a beam of white light passed through an alcohol solution of green leaves a red beam could be observed from the side (which was of course chlorophyll fluorescence). He correlated these phenomenawith the blue light coming from a light beam when entering some fluoritecrystals. Like Hauy, he considered the effect due to opalescence (light scattering).

Upon excitation in the UV the emission of light from Calcium sulphate was reported by Edmond Becquerel in 1842. He reported that the wavelength of the emission light was longer than that of the wavelength the incident light. In 1858 the invention of phosphoroscope enabled him to measure the decay times of phosphorescence.

In 1845, Sir John Herschel (son of the famousastronomer and the originator of the word photography)made the first observation of fluorescence from acidic solution of quinine sulfate.He stated

“Though perfectly transparent and colorless when held between the eye and the light, it yet exhibits in certain aspects, and under certain incidences of the light, an extremely vivid and beautiful celestial blue color ”

He termed this phenomenon “epipolic dispersion. (epipolic is a greek work meaning Surface)

(Source: Brewster, D. Philos. Mag. 1848, 32 (16), 401-412 (also published in Trans. R. Soc.

Edinburgh 1849, 16, 111-121)

Sir John Herschel reported his observation and discussed the superficial blue color of green fluorite crystals, also reported the similarity between the color from these crystals to that made with quinine solutions, and considered that it was also a case of epipolic dispersion. In contrast to Brewster theory the blue color of L. nephriticum extracts was attributed to ordinary dispersion by tiny particles in suspension by Sir Hershel.

When Brewster’s came to know about the epipolic theory proposed by Hershel, that contradicted his earlier views, he performed some more experiments in support of his theory proving that the phenomenon was not superficial. Since now Brewster proved Herschel wrong about the concept of superficial it was his challenge to support his concept experimentally. on the basis of polarization measurements, he proposed instead that “...unless this [property] is a new/different property of light, produced by a specific/peculiar action of some solid and fluid bodies...”

The Term Fluorescence and its Invention

In the history of photoluminescence a major event was recorded in 1952 which resulted due to the publication by Sir George Gabriel Stokes (Figure 6), physicist and professor of mathematics at Cambridge. Sir G G Stokes published his famous paper entitled “On the Refrangibility of Light”

explaining various concepts of behavior of light.

Stokes formed the solar spectrum by means of a prism. When he moved the solution of quinine through the visible part of the spectrum, there was

glowed with a blue light.

Stokes wrote,

Principle of Stokes’s experiment showing that a solution of quinine irradiated with UV emits blue light, whereas no effect is observed when it is placed in the visible part of the solar spectrum (Source: J. Chem. Educ. 2011, 88, 731–738)

Stoke experimented with a wide range of substances. He concluded that the dispersed light was always of longer wavelengths than the incident light. Later this statement became the Stokes law.This observations led Stokes to proclaim that fluorescence is of longer wavelength than the exciting light, which led to this displacement being called the Stokes Shift. However it was French physicist Edmond Becquerel to notice first that the emitted light is always of longer wavelength than the incident light. He also noted that the dispersion of light took place in all directions, hence, the fluid behaved as if it were self-luminous. He initially used the term true internal dispersion or “dispersive reflection” to describe this phenomenon but in a footnote, he wrote

In his second paper, Stokes definitely resolved to use the word fluorescence. (source: Stokes, G. G.

Philos. Trans. 1853, 143, 385–396. )

Becquerel, considered that phosphorescence and Stokes’s fluorescence were one and the same emission phenomenon, always with a finite duration that was simply shorter in the case of fluorescence and longer in the case of phosphorescence. He even advocated the term fluorescence to be abandoned, which according to his view was a short-lived phosphorescence.

Development in 20^th century in brief

• 1905 E. Nichols and E. Merrit: first excitation spectrum of a dye

• 1919 Stern and Volmer: fluorescence quenching

• 1923 S.J. Vavilov and W.L. Levshin: fluorescence polarization of dyes Solution

• 1924 S.J. Vavilov: first determination of fluorescence yield

• 1925 F. Perrin: theory of fluorescence polarization

• 1926 E. Gaviola: first direct measurement of nanosecond lifetime

• 1935 A. Jablonski: diagram

• 1948 T. Förster: QM theory of dipole-dipole interaction

THE DISCOVERY OF FLUORESCENT COMPOUNDS

In 1856, at the age of 18, William Henry Perkinset out with idea of making quinine by oxidizing allytoluidineinstead he accidentally produced the synthetic dye, mauve, a derivative of coal tar with an aniline base.

Adolph Von Baeyer Adolph Von Baeyer a German chemist, synthesized Spiro[isobenzofuran-1(3H),9'-[9H]

xanthen] -3-one, 3',6'-dihydroxy. He apparently coined the name “fluorescein”, from

“fluo” and resorcin, (resorcinol) which he reacted with phthalic anhydride. In 1905 he

• Fluorescence of polycyclic aromatic hydrocarbons was first reported by C. Liebermann (1880)

• In 1882 Paul Erlich used uranin (the sodium salt of fluorescein) to track secretion of the aqueous humor in the eye.

First in vivo use of fluorescence.

• K. Noack(1887) published a book listing 660 compounds arranged according to the color of their fluorescence.

• The term “fluorophore” was coined by R. Meyer (1897) to describe chemical groups which were responsible for fluorescence. this word was analogous to “chromophore” which was first used in 1876 by O.N. Witt to describe groups associated with color

Applications

In 1867 F. Goppelsröder introduced the term form"Fluoreszenzanalyse“ He performed the first fluorimetric analysis in history which was the determination of AI(III) by the fluorescence of its morin chelate.

Early Applications Of Photoluminescence

The fluorescent tube was one of the oldest applications of fluorescence. Edmond Becquerel in 1857, conceived the idea of coating the inner surface of an electric discharge tube with a luminescent material.Such tubes are similar to the fluorescent tubes that are made today. In fact, the inner coating is nowadaysmade of Europium (Eu II, Eu III), and Terbium (Tb III), so that addition of blue, red, and green lights yields white light

The first observation of the intense fluorescence of uranium in a NaF matrix was studied by Nichols and Slattery (1929)

• Hieger (1930) found that the fluorescence spectrum (measured photographically) of 1,2- benzanthracene resembled the spectra of some cancer-producing coal tars.

• Albert Coons (1941) the father of immunofluorescence was first to label antibodies with FITC.

• Brodie and Udenfriend(1943) introduce a simple method for the determination of quinine, and its dextro-rotary stereoisomer quinidine, in plasma.

• Saltzman (1948) introduces fluorimetric methods for salicylates in blood.

In 1952 Gregorio Weber synthesized dansyl chloride for attachment to proteins and used polarization to study protein hydrodynamics.

*these studies initiated the field of quantitative biological fluorescence.

The Instrumentation

Otto Heimstaedt and Heinrich Lehmann (1911-1913) developed the first fluorescence microscopes as an outgrowth of the UV microscope (1901-1904). The instrument was used to investigate the autofluorescence of bacteria, protozoa, plant and animal tissues, and bioorganic substances such as albumin, elastin, and keratin. Stanislav Von Prowazek (1914) employed the fluorescence microscope to study dye binding to living cells.

The first commercial instrument came in around 1955 i.e. in world war II. The only drug available at that time for treatment of malariahad huge side effect after certain level in blood.Using fluorescence, Drs.

Bernard Brodie and Sidney Udenfriend of Goldwater developed a special test to check the critical level at which a promising drug, such as Atabrine, would attack the malaria-causing parasites without causing adverse side effects for the patient. Their results determined the standard dosage used by the U.S. armed forces as a preventative for malaria.

In 1955 Aminco-Bowman (Silver Spring, MD) and Farrand Optical Company (Walhalla, NY) during World War II, took the challenge to combat malaria! During this periodfluorometer was developed to check the concentration of drug in patients plasma because of quinine shortage the only drug available for treatment of malaria

Summary

We discussed about the basic concept various phases and milestones of the discovery and the phenomena and its understanding. We also discussed about the discovery of fluorescent compoundsalong with the some early applications and Instrumentation.