There is disclosed a compound of formula (I) wherein each of X.sub.1 and X.sub.2 are independently NH-A-NR.sup.1R.sup.2, and wherein A is A C.sub.2-8 alkylene and R.sup.1 and R.sup.2 are independently selected from hydrogen, C.sub.1-4 alkyl, C.sub.2-4 hydroxy-alkyl and C.sub.2-4 aminoalkyl, or R.sup.1 and R.sup.2 together form a C.sub.2-6 alkylene group which with the nitrogen atom to which R.sup.1 and R.sup.2 are attached forms a heterocyclic ring, or an N-oxide derivative thereof, and wherein the compound (I) or its N-oxide derivative is optionally in the form of an acid salt derived from an organic or inorganic acid. Also disclosed is a method of its production and its uses, including its use in analyzing a cell or biological material and detecting the emitted fluorescence signal.