| 摘要 |
PROBLEM TO BE SOLVED: To provide a near-infrared absorption filter which has absorption maximum in a near-infrared area with minimized absorption in a visible part, and high toughness, and can exhibit satisfactory characteristics as a practical optical material. SOLUTION: The near-infrared absorption filter comprises a salt compound represented by the general formula (1), wherein: X<SP>1</SP>, X<SP>2</SP>, X<SP>3</SP>and X<SP>4</SP>each independently represent oxygen atom, sulfur atom, -CR<SP>5</SP>R<SP>6</SP>-, -CH=CH-, or NR<SP>7</SP>; Y<SP>1</SP>, Y<SP>2</SP>, Y<SP>3</SP>and Y<SP>4</SP>each independently represent an atomic group necessary for forming a 5-membered or 6-membered ring; R<SP>1</SP>, R<SP>2</SP>, R<SP>3</SP>and R<SP>4</SP>each independently represent an alkyl group; L<SP>1</SP>and L<SP>2</SP>each independently represent a methine chain consisting of 5 or 7 methine groups; and R<SP>5</SP>, R<SP>6</SP>and R<SP>7</SP>each independently represent hydrogen atom or an alkyl group. COPYRIGHT: (C)2009,JPO&INPIT
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