The invention relates to novel fluorescent dyes based on the following pyrenyloxy sulfonamide structure: wherein R1 is a leash joined to the pyrenyloxy group via an ether link containing generally a reactive functional group such as, activated carbonate, activated ester, amino group, azide or alkyne for conjugation with biomolecules; R2 and R3 are hydrogen atoms, or short alkyl chains, or cyclic rings with or without heteroatoms such as nitrogen, oxygen, sulfur, phosphorus. The spectral properties of the fluorescent dyes are sufficiently different in wave-lengths and intensity from fluorescein as to permit simultaneous use of fluorescein and/or more other fluorescent dyes with minimum interference and to avoid interference from endogenous green fluorescent protein in biological system. The dyes are non-ionic to facilitate their entry into cells for intracellular detection. The non-ionic structure also precludes undesired electrostatic reactions with ionic sites on biological components and structures. The dyes have bigger Stokes' shifts than other dyes with similar spectral properties allowing use of simpler, more efficient detection equipment, are not sensitive to pH, and have good solubility in aqueous solution.