In this contribution, we studied through experimental and relativistic DFT (R-DFT) calculations, the neutral complex fac-[Re(CO)(3)(1,10-phenanthroline-5,6-diol)Cl] (B1) as a potential precursor compound for designing new fluorophores suitable for confocal microscopy specially in walled cells. This work also describes via DFT calculations the electronic and spectroscopic properties of the facial (fac) and meridional (mer) isomers of this compound. The calculations shows that mer-isomer is 17.5 kcal/mol (in vacum) and 21.1 kcal/mol (when the solvent is considered) higher in energy with respect to the fac-isomer. The calculated emission spectra of B1, indicates an emission around 620 nm in acetonitrile in good agreement with the experimental reports for similar molecules. Finally, the Morokuma-Ziegler energy decomposition analysis shows a major lability for -Cl ligand which is ideal for designing new compounds replacing this ligand for another ancillary ligand suitable for biological applications. (C) 2017 Elsevier B.V. All rights reserved.