Abstract: The present invention aims at providing a compound that can be suitably used as a fluorescent dye or the like, a novel fluorescent dye and kit for easily detecting cells, a novel method for easily detecting cells or the like, and so on. A compound represented by the following formula (1) or a salt thereof: in the formula (1), R1 is a substituted or unsubstituted alkyl group having 1 to 12 carbon atoms or the like; R2 and R3 are each independently a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms or the like; R4 and R5 are each independently an alkyl group having 1 to 12 carbon atoms or the like; n is an integer of 1 to 4; and a and b are each independently an integer of 0 to 4.

Abstract: The present invention relates to providing a novel method for easily detecting tumor cells in a tissue derived from an organism. The present invention includes a fluorescent dye for detecting tumor cells in a tissue, including a compound that exhibits solvatochromism. The present invention also includes a method for detecting tumor cells or specifying a tumor removal area, including applying the fluorescent dye to staining of a tissue derived from an organism and to an organism.

Abstract: A two-photon-absorbing compound which is excellent in water-solubility, is excited by two-photon absorption in a near-infrared wavelength region, and emits a red fluorescence.