edited by
GEORGE L. GILBERT Denison University Granville. Ohio 43023
Phosphorescence: A Demonstration Submitted by:
Checked by:
Fitzgerald B. Bramwell and Mark L. Spinner City University of New York a t Brooklyn College Brooklyn, 11210 Madeline P.Goodstein Central Connecticut State College New Britain, 06050
The studv ~henomenais of basic im- of nhosnhorescence . . portance toward an understanding of photochemistry and nhotonhvsics. . " The teaching of such subiects which are often included in undergraduate-chemistry ~"rricula,can he made more effective through the use of demonstrations. Demonstrations of phosphoresrence phenomena are generally performed at liquid nitrogen temperatures using dilute solutions of aromatir organic molerules trapped in a rigid glass solvent.' Unfortunatelv, such demonstration samples require low tempraturesto maintain the rigidity of thesolid solution, are highly susceptible to quenching by oxygen and other impurities, and must be specially prepared a t the time of demonstration. A method we have found successful for making samples for use in phosphorescence demonstrations is to include them in a polymer matrix. Samples prepared in this manner are esse&ally permanent, relatively inert, and are effective for demonstration purposes at cryogenic temperatures and a t room temneratures. The proredure for making samples consists of preparing a lo-? M solution of a suitable aromatic organic compound in methyl methacrylate.? A minute amount uf benzoyl peroxide is added to the solution as an initiator of polymerization. The methyl methacrylate solutions are then transferred to quartz epr or nmr tuhes and deoxygenated by bubbling gaseous argon or nitrogen through them for several minutes. The solution is frozen and the tuhes dre then sealed under vacuum by a fme point torch. Polymerization of the sample occurs by totally immersing the sealed tuhes in an oil bath a t 60°C to 70% for 48 hr, followed hy sample annealing at 120°C for several hours. Annealing is necessary to remove any residual monomer present after the initial polymerization. Triphenylene and phenanthrene-dlo are solutes found to nroduce extremelv effective Dhas~horescencedemonstrations. more easily obtaked and less expensive practical grade naphthalene or hiphenyl make for leas dramatic but also satisfactory demonstrations. The phosphorescence lifetimes of research made and ~racticalmade samoles are shorn in the in the-above manner produce an intable. ~amGles tense phosphorescence upon short wavelength ultraviolet irradiation and are clearly visible in a darkened room for about six lifetimes a t either 7I0K or room temperature. For room temperature demonstrations of the >>> S . P . H When ~ ~ ~ crystallization finally commences, excess aupersaturation is quickly relieved, as bright orange (or yellow) HgIz precipitates.
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THIS JOURNAL, 32,9 (1955). The formation of orange Hglr was direovered accidentlv. hv. two Princeton underaraduates, Michael Orlando '53, and Jackson Moore '53, in the author's non-science chemistry course, where they were carrying out original research on the inhibition, by Hg2+,of the Landolt reaction. The author thereupan suggested their reducing the Hg2+concentration, believing that after its removal as Hg12, the normal iodine-clockreaction would continue and give blue-black. Nassau Hall ean boast of a colorful history. At the time it was built it was the largest college building in North America. On January 3, 1777 General Washington crossed the Delaware to seize the British ammunition stored there: his victorious Battle of Princeton followed. In 1796 it was perhaps the earliest undergraduate chemistrylaboratory in the world, where Dr. John Maclean, Professor of Chemistry, had the students, themselves, carrying out chemical experiments. At that time Europe still practiced apprenticeship; colleges in the New World gave only lecture demonstrations. In the late 1830s, several years bifore .Samuel Morse sent his first telegraph message, Dean Joseph Henry, using an electromagnet, sent "clicks" from his office in Nassau Hall to his home nearby to alert his servants that he was coming home shortly, and to start heating water for his tea. %ulfurie acid, used in the original Landolt studies, is not required. 6 "Niagara brand" household starch is recommended. Wotice, in the equations and chart which follow, that Hf forms and the p H falls during reaction. Sorum, C. H. et al., J . Amer. Chem. Soc., 74,219 (1952).
