PREFACE V 



In their paper on luminescence spectroscopy, Becker and Kasha 

 deal with the primary step for the utilization of energy by the chloro- 

 phyll system, and in particular, the question of which electronic state 

 of chlorophyll is involved in the primary step. Omitting unessential 

 details of tlie physical theory, they consider chiefly the role of n-n-- 

 transitions in the chlorophylls, the importance of intercombinations in 

 these molecules, and the possible interaction of the ethylenic potential 

 function with the electronic transitions in the chlorophylls. 



In the first of the two papers that follow, Arnold briefly presents 

 some new data on delayed light production in green plants, together 

 with a hypothesis to account for the observation that light saturation 

 of the delayed light emission occurs at lower intensities than light 

 saturation of photosynthesis. French then gives a summary discussion 

 of fluorescence spectrophotometry of major photosynthetic pigments, 

 including phycoerythrin, bacteriochlorophyll, chlorophylls a, b, and 

 c, protochlorophyll, phycobilins and chlorophylls in the red algae, and 

 a new leaf pigment that was discovered with a fluorescence micro- 

 scope. An apparatus for automatically plotting the spectral energy 

 distribution of weakly emitting light sources, and its application to the 

 study of pigments in living cells as well as in solution, is described 

 and illustrated in adequate detail. 



The kinetic approach to the mechanism of chemiluminescence of 

 the 2,3-dihydrophthalazine-l,4-diones (DPD's or phthalic hydrazides, 

 of which luminol is probably the best known derivative ) is stressed in 

 the paper by Wilhelmsen, Lumry, and Eyring. The theory of absolute 

 reaction rates is applied in interpreting the rates of excitation, radia- 

 tion, and quenching of the molecules involved in light emission. New 

 data are included in regard to the relationships of the reaction to 

 oxygen, and the nature of intermediary compounds and end products 

 is discussed. 



Chemiluminescent, fluorescent, and absorption spectra in relation to 

 molecular structure, with particular reference to DPD and naphtho- 

 quinone derivatives, as well as dimethylbisacridinium nitrate, are dis- 

 cussed in the joint paper by Spruit and Spruit-van der Burg. The in- 

 fluence of factors such as temperature and pH is included, and the 

 significance of the photochemical inactivation of bioluminescence in 



