Novel onium salts and the use thereof as photoinitiators

摘要: Sulfonium, selenonium, arsonium, ammonium and phosphonium salts, useful as photoinitiators, comprise: a chromophore which absorbs visible radiation, the (1) having removable positive hydrogen ion (2) exhibiting higher energy occupied molecular orbital than at least one other substituent attached to S, Se, As, N or P atom of salt; group links salt, partially preventing π resonance between substituents in comprising an electron withdrawing lower unoccupied chromophore; and, anion; salts being capable, upon exposure forming Bronsted acid.