This ppt conains the history,introduction,theory and factors affecting fluorescence.This can me most helpful for the analysis students who were looking for the fluorescence topic with easily understandable way.

1. By,
Jaswanth Gowda B H
1st year M.Pharm(Pharmaceutics)
Vivekananda college of
pharmacy

2. The term fluorescence comes from the mineral
fluorspar(calcium fluoride) when Sir George
G.Stokes observed in 1852 that fluorspar would
give off visible light(fluorescence) when exposed to
electromagnetic radiation in the ultraviolet
wavelenth.

3. Introduction:
(#)Many substances are able to absorb uv (or) visible
Light energy but soon they lose energy as heat
through collisions with neighbouring atoms.
(#)Only few substances that lose part of energy as
heat and emit the remaining energy as EMR of a
wavelengh longer than that absorbed.
(#)The following process of emitting radiation is
called as luminescence.

4. Luminescence is of two types:-
1)Fluorescence
2)Phosphorescence
 FLUORESCENCE:-
*When a beam of light is incident on certain
substances, they emit visible radiations.This phenomenon is
known as fluorescence and the substances shows this
phenomenon are known as fluorescent substances.
*This is instantaneous and starts immediately after the
absorption of light and stops as soon as the incident light cut
off.
*They re-emit radiations generally within 10¯⁶ to 10¯⁴
second of absorption.

5. PHOSPHORESCENCE:-
*When light radiation is incident on certain
substances,they emit light continuously even after the
incident light cut off and substances showing this
phenomenon is known are known as phosphorescent
substances.
*They re-emit excess radiation within 10¯⁴ to 20
seconds or longer.
*Thus,the life-time of phosphorescence is much
longer than fluorescence.

6. THEORY OF FLUORESCENCE:-
*In order to understand the theory of
fluorescence, one should understnd the meaning of
singlet and triplet state.
*Ground singlet state:- electrons are paired.
*Triplet state :- unpaired electrons of same spin.
*Singlet excited state:- unpaired electrons but of
opposite spin.

7. *When the molecules or atoms absorb uv or
visible radiations of a proper frequency,one or more of
the paired electrons get raised to an EXCITED
SINGLET STATE from GROUND SINGLET STATE.
*In this excited state,the spin of the electron
doesn’t undergo any change and the net spin is still
zero.
*One more possibility is that one set of the
electron spin may have undergone unpairing
resulting in two unpaired electrons,which makes an
excited triplet state.
*small possibility of direct tansition from SGS
to TES.

8. *When molecules are irradiated with light of
appropriate frequency,it will be absorbed in about
10¯¹⁵ Seconds,then it moves from ground to first
excited singlet state.
*From excited singlet state,one of the following 3
phenomenon will probably occur,depending on the
molecule.
( 1)excited molecule may return to ground state
by collisional deactivation without emitting any
radiation.

9. (2)excited molecule may emit uv or visible light
photon,this is known as fluorescence.
(3)excited molecule are quite stable so it will
undergo transition from singlet excited state to triplet
state and later return to ground state with emission of
uv or visible light photon.this is known as
phosphorescence.
*process of crossing from singlet state to triplet
state is termed as intercrossing system.

11. Factors affecting fluorescence:-
 Nature of molecules
 Nature of substituents
 Effect of concentration
 Adsorption
 Light
 Oxygen
 Photodecomposition
 Temparature and viscosity

12. Nature of molecules:-
*Not all molecules can show the phenomenon of
fluorescence ,only few which are able to absorb uv or
visible can show.
*Greater the absorbance of molecule,more the
intense of its luminescence.
*molecules containing conjugated double
bonds(ex:-1,3 pentadiene etc..) are much suitable for
this.
*aliphatic and saturated cyclic compounds(ex:-
butane,cycloalkanes etc..) are not sutable for this study.

13. Nature of substituents:-
*Electron donating groups like –NH2, -OH often
enhance fluorescence, but –SO3H, -NH4 and alkyl
group donot have much effect on fluorescence
*Electron withdrawing groups like –COOH,
-NO2, -N=N- and halides decrease or even destroy
fluorescence.
*If high atomic number atom is introduced into a
π electron system,it decreases fluorescence but
enhances phosphorescence.

14. Effect of concentration:-
*It’s already stated that fluorescence is
proportional to concentration but it must be
highlighted that the equation aplies only to small
values
*If greater the concentration then there won’t
be linearity in calibration curve,leads to self
quenching.

16. Adsorption:-
*extreme sensitiveness of method requires
very dilute solution,10-100 times weaker than those
employed in spectrofluorimetry.
*adsorption of fluorescent substance on
container walls can cause major problems.
*strong stock solutions are diluted.
ex:- quinine.

17. Light:-
*Monochromatic light is required for
excitation.
Oxygen:-
*it oxidises the fluorescent to non fluorecent
substances.
*due to paramagnetic property of molecular
energy,it decreases fluorescence.

18. Temperature and Viscosity:-
*increase in temparature leads to collissional deactivation
thus results in decreased fluorescence.
*increased viscosity leads to decreased collisional deactivation
which in turn results increased fluorescence.
pH of solution:-
*alteration in ph of solution show significant effect on
fluorescence.
Phenols:- acidicundissiciate formNo fluorecence.
alkalinedissociated formgood fluorescence.

19. Reference:-
1.Instrumental Methods of Chemical Analysis
by G.R. Chatwal
2.Instrumental Methods of Chemical Analysis
by B.K. Sharma

20. THANK YOU