PROBLEM TO BE SOLVED: To provide a near-infrared fluorescent pigment having a fluorescent wavelength on a longer wavelength side than fluorescein and inverted U-shaped naphthofluorescein (1) which are already known and to provide a diagnostic imaging material, which contains such a near-infrared fluorescent pigment, and a diagnostic imaging method which is carried out by using such a diagnostic imaging material.SOLUTION: Linear naphthofluorescein (2) has the condensation positions of two benzene rings at [b, i] of xanthene among naphthofluoresceins having structure in which two benzene rings are added to both the sides of the xanthene skeleton of fluorescein, respectively, the naphthofluorescein (2) having a fluorescent wavelength on a longer wavelength side than already known fluorescein and inverted U character-type naphthofluorescein (1).COPYRIGHT: (C)2013,JPO&INPIT【課題】従来知られているフルオレセインや逆U字型ナフトフルオレセイン(1)よりもさらに長波長側に蛍光波長を有する近赤外蛍光色素を提供し、併せて、そのような近赤外蛍光色素を含む画像診断材料と、そのような画像診断材料を用いて行う画像診断方法とを提供する。【解決手段】フルオレセインのキサンテン骨格の両側にベンゼン環を1つずつ付加した構造のナフトフルオレセインのうち、2つのベンゼン環の縮合位置がキサンテンの[b、i]である直線型ナフトフルオレセイン(2)は、従来既知のフルオレセインや逆U字型ナフトフルオレセイン(1)よりもさらに長波長側に蛍光波長を有する。【選択図】図5
