Complex sentence: Gill probably confused luminol with "lophine" (2,4,5-triphenyl-1 "H"-imidazole), which is mentioned in the sources that Gill cites, and which is also chemiluminescent, and which was first prepared in 1844 by Auguste Laurent.
Split into simpler sentences: Gill probably confused luminol with "lophine" (2,4,5-triphenyl-1 "H"-imidazole), which the sources he cites do mention. Lophine is also chemiluminescent, and was first prepared in 1844 by Auguste Laurent.