The prodigious development in the field of fluorescent probes and imaging techniques has enabled researchers to visualize specific subcellular organelles and characteristic cellular processes in living cells. Among the various organelles, the nucleus stocks all the genetic material and controls most of the cellular events comprising DNA replication, mRNA synthesis and processing. Most nucleus targeting sensors have been designed by incorporating nucleustargeting ligands, like Hoechst or peptides, but even slight structural modifications lower their targeting ability drastically and thus require longer incubation times for localizing. Existing methods for monitoring mitotic division often involve cell fixation or genetic engineering of fluorescent cell-cycle reporters, which is a tedious process, requires skilled professionals and thus limits their applicability for real-time studies of live cells. Consequently, still there is a lack of fluorescent probes for live-cell imaging of cell-cycle progression, and most of them are frequently limited for their applicability due to UV-excitation, photo bleaching, poor aqueous solubility and sensitivity to subcellular environments. Thus, it is critical to develop new cellpermeable freely water soluble molecular probes for nucleus staining to enable real-time visualization of biological events during cell-cycle progression in live cells. Here, we introduce a diazaoxatriangulenium cation (DAOTA + ) based highly water soluble probe, Nuc-DAOTA + endowed with long fluorescence lifetime, high photo-stability, and cellpermeability for the direct visualization of cycle cell in live cells. Nuc-DAOTA + exhibits an increase in fluorescence intensity and lifetime upon specifically binding with DNA but not with RNA (ribonucleic acid) or water soluble protein BSA (bovine serum albumin), that is also a key feature of this probe. Vilar et al. has previously investigated some triangulenium dyes as optical probes for nucleic acids of different topologies mainly G4 secondary structures, dsDNA (double stranded deoxyribonucleic acid) and ssDNA (single stranded deoxyribonucleic acid) by using fluorescence lifetime imaging microscopy. They found that the diazaoxatriangulenium based DAOTA-M2 showed better nucleus targeting with a significant enhancement of the fluorescence lifetime after binding with G-quadruplexes, in comparison to other forms of nucleic acids. Furthermore, Lacour et al. has designed a pH-sensitive DAOTA + based fluorophore functionalized with a hexadecyl side chain and explored it for the selective staining of the late endosomes in both live and fixed cells.