**9. Conclusion**

The experimental and theoretical charge-density analysis has been performed to understand the topological and electrostatic properties of the 1–10 phenanthroline hydrate molecule. The crystal structure reveals the molecule forming O▬H⋯O, O▬H⋯N, C▬H⋯O and C▬H⋯N types of interactions with the neighboring molecules. Furthermore, photoluminescence studies indicate that the hpp is fluorescently active in solution at room temperature and reveal that the emission originate from an excited state-charge transfer state π-π\* which is proven by TD-DFT analysis.

The AIM analysis shows the existence of a bond critical point (BCP) between N1B and H11W. We notice that ρ = 0.034 is very weak and Δ = 0.091 > 0 which confirms that this interaction is the strongest interaction in the molecule (hydrogen-bonding interaction). These results are in good agreement with those obtained by experimental refinement.

The structural, topological and electrostatic properties of the 1–10 phenanthroline hydrate molecule obtained from the X-ray diffraction method may be useful to design a new candidate of blue-light luminescent materials.
