EXCITATION OF POLYENES AND PORPHYRINS 



109 



BAND I 



BAND m 



PYRRO PORPHYRIN TSL 

 (PORPHYRIN POLARIZATION) 



4-BENZOYL- 

 MESOPORPHYRIN TTTT 

 (CHLORIN POLARIZATION) 



t I 2 5 

 — *- »- *. 



m=60 



11^ ! 



fK 7 8 



" >■- >- > 



4-BENZOYL 



m=zo 



CHLORIN-P^ AND X 



RHODIN-gTj (^ 



(CHLORIN POLARIZATION) 



3-FORMYL 3-ETHYL 



7-HYDRO 



8-HYDRO 



8-HYDRO 





6- CO OH 



7-HYDRO 3-ETHYL 3-FORMYL 



CHLORIN-f^ o 



771-0 ^ 



RHODIN-^Tj 

 7n= 50 



CHLOROPHYLL 



(CHLORIN POLARIZATION) 



7-HYDRO 8-HYDRO Mg 3 4 



Fig. 2-21. Spectroscopic moment vector sums for typical polysubstituted porphyrins. 



Then, adding the vectors in the directions given in Fig. 2-20 and squaring, 

 we have, in general, for the change in intensity 



/ = (Ms - M^y + (Ml + M, + M,v - .l/J" 



(2-15) 



for band I in porphyrin polarization and for band III in chlorin polari- 

 zation; and 



/ = (Ml - M.)- + (M3 + M4 + M.v - ^rj- 



(2-16) 



for band III in porphyrin polarization and for band I in chlorin polari- 

 zation. For chlorins, these expressions simplify to 



