A compound represented by the following general formula (I), wherein ring A and ring B each independently represent a benzene, naphthalene, or heterocyclic ring which may be substituted; R1 and R2 each independently represent an alkyl group having 1 to 8 carbon atoms which may be substituted; R1 and R2 may be linked together to form a ring; a methylene group of the alkyl group having 1 to 8 carbon atoms may be replaced by —O— or —CH═CH—; Anq− represents a q-valent anion, where q is 1 or 2; p represents a coefficient to keep the charge neutral.