Optical filter and imaging device

A sqaurylium-based dye represented by formula (AI) or formula (AII):

• where
• X is independently a bivalent organic group represented by formula (1) or formula (2), in which one or more hydrogen atoms are optionally substituted with a halogen atom or an alkyl group or alkoxy group having 1 to 12 carbon atoms:
• —(CH2)n1— (1)
• in the formula (1), n1 is 2 or 3;
• —(CH2)n2—O—(CH2)n3— (2)
• in the formula (2), n2 and n3 are independently an integer of 0 to 2, and n2+n3 is 1 or 2;
• R1 is independently a group represented by formula (4-2):
• where R13, R14, and R15 independently represent a hydrogen atom, a halogen atom, or an alkyl group having 1 to 4 carbon atoms, with the proviso that
• a combination that all of R13, R14 and R15 are hydrogen atoms is not included,
• when two of R13, R14 and R15 are hydrogen atoms, the other one is halogen atoms, and
• when one of R13, R14 and R15 is a hydrogen atom, the other two are independently a halogen atom or an alkyl group having 1 to 4 carbon, atoms;
• R2 independently represents a hydrocarbon group having 1 to 25 carbon atoms in which one or more hydrogen atoms are optionally substituted with a halogen atom, a hydroxy group, a carboxy group, a sulfo group, or a cyano group and which optionally contain an unsaturated bond, an oxygen atom, or a saturated or unsaturated ring structure between carbon atoms;
• R3, R4, R5, and R6 independently represent a hydrogen atom, a halogen atom, or an alkyl group or alkoxy group having 1 to 10 carbon atoms;
• and
• n is 2 or 3.