TMO is (2,4,6-trimethyl benzoyl)bis(p-tolyl)phosphine oxide, CAS 270586-78-2 is a free-radical photoinitiator and viable alternate to TPO.

Photoinitiator 784, also known as PI-784, is a highly efficient photoinitiator for free-radical polymerization. It has a broad absorption spectrum,

Diphenyl[4-(phenylthio)phenyl]sulfonium Hexafluoroantimonate is a sulfonium based cationic photo-initiator.