| abstract |
An indolium compound is represented by formula (I): n n n n n n n n n n Ring A: a benzene or naphthalene ring. Ring B: 5- or 6-membered heterocyclic or aromatic ring. Z: alkyl group having 1-8 carbon atoms, may be substituted with a halogen atom or interrupted by —O—, —CO—, —OCO—, or —COO—, a sulfonyl group having a hydrocarbyl group having -8 carbon atoms, a sulfinyl group having a hydrocarbyl group having 1-8 carbon atoms, an alkylamino group having an alkyl group having 1-8 carbon atoms, a dialkylamino group having alkyl groups having 1-8 carbon atoms, a cyano group, a nitro group, a hydroxyl group, or a halogen group. R 1 : group represented by formula (II) or (II′). R 2 : organic group having 1-30 carbon atoms or group represented by formula (II), (II′), or (III). Y: group represented by formula (III). n: integer 0-4; An m− : m-valent anion, m is 1 or 2. p: coefficient for neutral charge: |