Demonstration 25.
Lightsticks.
The unique properties of the peroxyoxalate chemiluminescent system (described in detail in our next demonstration) permit many applications which cannot be served by electrically powered devices [1]. For example, in areas where the possibility of explosion exists chemical light can be employed safely, since, being a cold luminescent source, it cannot be a source of ignition. An amazing variety of uses has been developed in recent years: emergency lights for use in power failures; small portable lights for camping, backpacking, and jogging; marking lights for life jackets; lures for commercial fishing; and a wide spectrum of novelty uses.
American Cyanamid’s Cyalume products are currently the only chemical light devices being marketed for marking and illumination [2,3]. These products are based on the reaction of bis(2,4,5-trichlorophenyl-6-carbopentoxyphenyl)oxalate (CPPO) with hydrogen peroxide [4]:
This particular oxalate ester was selected from a large number of candidate compounds because of good storage characteristics, high efficiency and adequate solubility in the phthalate ester reaction medium. Under practical conditions CPPO has given quantum yields as high as 17%. Several different fluorescers can be employed to produce different colours [5]: 9,10-diphenylanthracene (blue), 9,10-bis(phenylethynyl)anthracene (green), and 1-chloro-9,10-bis(phenylethynyl)anthracene (yellow). Recently a red-emitting Cyalume lightstick was introduced. This device employs a fluorescent red pigment molded into a plastic tube which absorbs the light emitting from a yellow reaction and re-emits it as red via a trivial energy transfer process. Experiments with a number of red-emitting fluorescers indicated that most of these compounds were much less stable to the peroxyoxalate reaction conditions than fluorescers emitting at lower wavelengths. Thus the energy transfer device actually produced twice the light capacity of the best reaction with a red fluorescer dissolved in the reaction solvent.
Preparation. No specific preparation is needed. The light sticks are propriety devices that can be purchased from ‘outdoor supply’ shops (e.g., ‘Famous Army Stores’). They consist of a plastic outer tube some 15 cm long and 15 mm diameter
Demonstration. Simply follow the instruction on the pack. Bend the outer plastic tube to break the inner glass tube containing hydrogen peroxide. Mix the solutions by shaking the light stick.
You can increase or decrease the brightness of lightsticks by increasing or decreasing the temperature but they cannot be turned off, i.e., they will continue to give out light until the reaction is complete (one of the reactants is used up). Generally the rate of a reaction doubles with each increase of about 10 degrees and is known as Q10. Placing a Light Stick in a domestic deep-freezer would reduce the temperature from ambient, say +20 oC, to -20 oC. These particular sticks last for some 8 hours at 20 oC, so at 10oC we might expect the light intensity to fall to half and last for 16 hours. Similarly at 0oC the light intensity would fall to half again, 1/4 of its original intensity and last for 32 hours. So at -20oC it might emit 1/16 of the original light energy but last 128 hours rather than 8 hours.
References.
1. A.G. Mohan, “Peroxyoxalate chemiluminescence”, in Chemi- and Bioluminescence, ed. J.G. Burr, New York - Basel, Marcel Dekker, Inc., 1985, pp. 245-258.
2. M.M. Rauhut, in Chemiluminescence and Bioluminescence, eds. M.J. Cormier, D.M. Hercules and J. Lee, New York, Plenum, 1973, pp. 451-460.
3. M.M. Rauhut, in Encyclopaedia of Chemical Technology, 3rd ed., ed. Kirk-Othmer, vol. 5, 1980, pp. 437-439.
4. L.J. Bollyky and M.M. Rauhut, U.S. Patent No. 3,597,362 (1971) to American Cyanamid.
P.J. Hanhela and D. Paul, Aust. J. Chem., 1981, 34, 1669-1717.