9433
The quantum yield of charge separation is modulated by the two photochromes : one isomer of each quenches the porphyrin excited state , reducing the quantum yield of electron transfer to near zero .
 porphyrin
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 porphyrin