QUENCHING EFFICIENCY 



'83 



The experiments of Li\'ingston and Ke (1949) dealt largely with what 

 appears to be true chemical quenching: changes due to reversible reactions 

 of excited chlorophyll molecules with certain organic and a few inorganic 

 molecules. In some cases, at least, this interpretation was confirmed by 

 observations of the constancy of the absorption spectrum, and by the in- 

 stantaneous character of the change. 



Table 23.IIID 



NONQUENCHERS OF CHLOROPHYLL FLUORESCENCE IN METHANOL, EtHANOL OR AcETONE" 



(after Livingston and Ke, 1949) 



Reagent Solvent [Q], m./I. Fo/F 



Nitropropane MeOH .09 1 .00 



Nitropropane MeOH 0.2 1.02 



Butvl nitrate MeOH 0.9 1 .02 



Butvl nitrite MeoCO 0. 138 101 



Phenvlhvdroxvlamine MeOH 0.021 1 .02 



Phenvlhydroxylamine MeOH . 07 1 . 05 



Aniline Et.OH 0.16 1 .02 



Hydrazine MeoCO 1 .05 1.0 



Urethan MejCO .07 1.0 



Thiourea Me.CO 0.02 1 .0 



2-Aminopvridine MeOH .08 1 .00 



Phenvlurea MeOH 0.05 1.01 



Urea^ MeOH 0.19 1.00 



Guanidine carbonate MeOH (Satd.) 1.0 



Phenol MeOH 0.09 1.0 



Hvdroqninone* MejCO 0.03 1.0 



Phenolphthalein MeOH .04 1.0 



Dimethvlo;lvoxime MeOH . 07 1.0 



/e/7-Hexvlmercaptan MeOH 0.11 1 . 00 



Benzaldehvde MeOH 0.38 1.0 



Benzoic acid Me.CO 0.08 1.0 



Camphor MeOH 0.15 1.0 



Boric acid MeOH (Satd.) 1 .00 



Sodium methoxide MeOH 0.05 1.0 



Sodium cyanide MeOH 0. 15 1 .01 



Sodium oxide MeOH 0.11 1.0 



Nitrous oxide EtOH (605 mm.) 1.0 



Carbon dioxide EtOH (576 mm.) 1.0 



Carbon monoxide MeOH (640 mm.) 1 .00 



Potassium thiocyanate MeOH 05 1 . 02 



Potassium thiocyanate MejCO . 004 . 92 



" Other nonquenchers: a^^corbic acid; alkali iodide (Evstigneev and Krasnovsky, 

 1948): allylthiourea(r/. naffe789). 



^ The measurements of Evstigneev and Krasnovsky (1948) indicate that hydroquin- 

 one at much higher concentrations has some quenching action, but is less efficient than 

 2-diaminopyridine, the weakest quencher in Table 23.IIIC. 



Li\nngston and Ke used a 1.2 X 10~^ molar solution of chlorophyll a 

 in methanol, ethanol, ether or acetone, which they excited by the mercury 

 line 435.8 mju, or bj^ a red band centered at 645 m/z. Tables 23.IIIC and 

 D show that quenching was similar for both types of excitation. The 

 quenchers are listed in the first table in order of declining efficiency; it is 



