Luminescence
Luminescence is defined as the emission of light that is not a direct result
of applying an electrical current to a filamenti. There are many forms of
luminescence such as fluorescence, phosphorescence, bioluminescence,
triboluminescence, and chemiluminescence.
Fluorescence is the absorption of light of one energy and the immediate
release of light at the same or more commonly at a slightly different energy. This
is seen in fluorescent paint. Phosphorescence is the absorption of light at one
energy and the delayed release of light. This is seen in glow in the dark paint and
dyes.
Bioluminescence is the release of light by plants or animals. Fireflies,
algae, and deep sea organisms produce light. Mosquito Bay in Vieques, Puerto
Rico has such a high concentration of bioluminescent algae, that is commonly
called “bioluminescent bay” and tourist tours are regularly scheduledii.
iii
Firefly
iv
Kayaking in Mosquito Bay, PR Light emitting sea creatures
Chemiluminescence
The most common way in which chemical reactions dispose of excess energy is
by releasing heat. This is exothermicity. Some chemical reactions dispose of
excess energy by releasing it in the form of light. This is called
chemiluminescence. This is normally done by electrons in an excited state
cascading to lower energy molecular orbitals with the simultaneous emission of
light.v
In today’s demonstration luminol
will be reacted with sodium
hydroxide, hydrogen peroxide and Fe(III) to produce a triplet excited state
dianion, which will proceed first to the singlet state and then go onto the ground
state. The energy released will be light with a lambda max of approximate 450
nmvi. What color do you expect? (What is the color of 450 nm light?)
Mechanism:
A reasonable progression of the reaction mechanism is listed.vii
Electron excitation and decay cascade
viii
In today’s demonstration a sodium hydroxide solution will be mixed with the
luminol, hydrogen peroxide, Fe(III) solution.
Luminol is also used by forensic detectives. It is sprayed at a darkened crime
scene, if iron is present from the hemoglobin of blood, it will glow.
ix
Triboluminescence
Triboluminescence is when light is produced by materials being crushed, rubbed,
or mechanically stressed. You can examine this phenomena on your own with a
dark room and Wint-O-Green Lifesavers.x Let your eyes adjust to the dark.
Chomp down, with your mouth open (like a monster), and see the sparks (also
like a monster). We would do this in lab, but eating is not allowed in any lab,
especially organic chemistry lab.
Today’s lab is a demonstration lab. No pre-lab notebook is required. It will not be
included on the final exam.
Revised November 18, 2013, S.L. Weaver
i
Webster’s New Collegiate Dictionary, G. & C. Merriam Co., Springfield MA, 1980 p 574,678
Abe’s Snorkel and Bio-Bay Tours, Vieques PR http://www.abessnorkeling.com/bio_bay_tour.shtml, (April 6,
2011)
iii
National Geographic Article on Fireflies, http://animals.nationalgeographic.com/animals/bugs/firefly/ (April
6, 2011)
iv
Deep water bioluminescent organisms. Photo: HBOI Image courtesy of Islands in the Sea
2002, NOAA/OER.
v
nd
Skoog, D. A, West D. M., Principles of Instrumental Analysis,2 Ed, Saunders, 1980, p 280-286
vi
The Chemiluminescence of Luminol, T.G. Chasteen, www.shsu.edu/~chm_tgc/JPPdir/JPP1999/ (April 6,
2011)
vii
nd
McRitchie-Ticknor, D., Gabrielsen, B., Organic Chemistry in the Laboratory, 2 Edition, Kendall Hunt
Publishing, Dubuque Iowa, 1983, p 247-251 and The Chemiluminsence of Luminol
http://www.chm.bris.ac.uk/webprojects2002/fleming/mechanism.htm (April 7, 2011)
viii
Luminescence http://web.me.com/dtrapp/eChem.f/labP17-Luminescence.html
(November 16, 2011)
ii
ix
Bureau of Criminal Aprehension, Minesota of Public Safety
https://dps.mn.gov/divisions/bca/bca-divisions/forensic-science/Pages/forensic-programs-crimescene-luminol.aspx (November 18, 2013)
x
Wintergreen Candy and other Tribololuminescent Materials, Linda M. Sweeting,
http://pages.towson.edu/ladon/wg/candywww.htm (April 6, 2011)