EXCITATION OF POLYENES AND PORPHYRINS 



111 



above the unsubstituted intensity for bands I and III. Some "negative" 

 values are shown, where it is supposed that the direction of the vectors is 

 just reversed from the direction in adjacent compounds in the figure. 



m 



100 



PHYLLO TYPE 



ETIO TYPE 



150 



224 



RHODO TYPE 



X 



HEMIN 



165 



200 



BAND I 



Fig. 2-22. Observed (o- 



porphyrins. (For meaning of negative values, see text 



-o) and calculated (x-- 



BAND in 



x) total spectroscopic moments for 

 For the diimino compound, 



33, the points have been displaced to the left as indicated.) 



It can be seen that many of the distinctive changes in the spectra are 

 correctly reproduced, such as the differences between "phyllo," "etio," 

 and "rhodo" types described by Stern and Wenderlein (1936, V). The 

 "chlorin"-"rhodin" differences in the compounds examined in Fig. 2-23 

 are reproduced especially well. Chlorins have a positive m^ in Eq. 

 (2-15a), and rhodins and 6-compounds, negative, making their band I 

 moments smaller by 50 units. The theory given here could also be 

 applied to the porphins and chlorins studied by Dorough et al. (1951, 

 1952). 



Discrepancies. The most conspicuous discrepancies are in those por- 

 phins with one strong acid substituent, such as rhodoporphyrin XV, its 



