27165
In fact , at low pH values , the spectra show a blue - shifted emission , resembling that of unprotonated acridine , while at slightly acidic and alkaline pH the fluorescence features a red - shifted band similar to that of acridinium cation .
 acridinium
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 acridinium