A dithienophosphorine compound having a cation represented by the formula

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(wherein Y represents an oxygen atom or a sulfur atom; R.sup.1 represents a hydrogen atom, an alkyl group, an alkenyl group, an alkynyl group, an aryl group, or a heteroaryl group; R.sup.2 represents a hydroxy group, an alkyl group, an alkoxy group, an alkenyl group, an alkynyl group, an aryl group, or a heteroaryl group; R.sup.3, R.sup.4, R.sup.5, and R.sup.6 each independently represent a hydrogen atom, an alkyl group, an alkenyl group, or an aryl group; R.sup.7 and R.sup.8 each independently represents an arylene group or a heteroarylene group; R.sup.9 and R.sup.10 each independently represent a hydrogen atom, a halogen atom, a sulfonyl group, an alkyl group or an aryl group; each group may have one or more substituents; and R.sup.3, R.sup.4, and R.sup.7 may bind to each other and/or R.sup.5, R.sup.6, and R.sup.8 may bind to each other to form a ring together with an adjacent nitrogen atom) is an organic compound that has a maximum absorption wavelength in the NIR-II region (from 1000 to 1500 nm) although the molecular weight thereof is not extremely high, and that has excellent solubility in organic solvents and high structural selectivity.

The disclosure concerns phosphorus compounds of formula (I), (II) and (III) and methods of synthesising these compounds. The phosphorus compound can be a cyclic phosphorus compound. The method comprises reacting a compound having two Michael acceptor groups with a hypophosphite ester, acid, salt or solvate thereof and an optional organosilicon compound. The diene can be a cyclodiene.

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In one aspect, the disclosure relates to xanthene-, thiazine-, and oxazine-based dyes containing a phosphinate ester group and having near-infrared (NIR) absorption and methods of making the same. The fluorescence lifetimes and stabilities of the dyes can be tuned by modifying the molecule cores, making them suitable for a variety of chemical labeling, imaging, and other theranostic applications. This abstract is intended as a scanning tool for purposes of searching in the particular art and is not intended to be limiting of the present disclosure.

Fluorescent dyes useful for preparing fluorescent metal ion indicators, the fluorescent indicators themselves, and the use of the fluorescent indicators for the detection, discrimination and quantification of metal cations are provided.