**2. Structural commentary**

The structure of {(C12N2H8)H2O} is trigonal; space group P31, the molecular structure, is shown in **Figure 1**. The asymmetric unit is formed from three molecules of phenanthroline and three molecules of water. The crystal structure is built of successive rings formed by six molecules of phenanthroline; the centre of these

*View of the hpp molecule, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level, and H atoms are shown as circles of arbitrary radii.*

*Strongly Fluorescent Heterocyclic Molecule: Crystallography, 3D Hydrogen-Bonded, Fluorescence… DOI: http://dx.doi.org/10.5772/intechopen.90271*

rings are the three molecules of water. Bond lengths and valence angles compare well with the average values from related phenanthroline structures [6, 7].

## **3. Supramolecular features**

and viscometric titration, thermal denaturation and differential pulse voltammetry have been employed for 1,10-phenanthroline complexes to probe the details of DNA binding [2, 3]. The influence of the presence of nitrogen atoms on the fluorescence spectral maxima of aromatic molecules is our interest, including compari-

The structure of {(C12N2H8)H2O} is trigonal; space group P31, the molecular structure, is shown in **Figure 1**. The asymmetric unit is formed from three molecules of phenanthroline and three molecules of water. The crystal structure is built of successive rings formed by six molecules of phenanthroline; the centre of these

*View of the hpp molecule, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50%*

*probability level, and H atoms are shown as circles of arbitrary radii.*

son of the spectra in polar and non-polar solvents. Such studies facilitate to understand the features of chemical bonding in molecules from the topological analysis of electron densities [4] and various electrostatic properties of molecules. These fundamental properties are directly related to the properties of materials [5]. The present compound, viz. {(C12N2H8)H2O}, has been characterized with X-ray crystallography, and we are interested in fluorescence properties. The fluorescence spectra of the present compound have been obtained in various conditions. The time-dependent density functional theory (TD-DFT)/quantum theory of atoms in molecules (QTAIM)/orbital analysis and molecular electrostatic potential (MESP)

theoretical calculations have been applied too.

**2. Structural commentary**

*Electron Crystallography*

**Figure 1.**

**78**

The crystal structure is built of successive rings of phenanthroline and water molecules extending parallel to (001) plane that are connected by an extensive three-dimensional hydrogen-bonded network of the type O▬H⋯O, O▬H⋯N, C▬H⋯O and C▬H⋯N (**Table 1** and **Figure 2a**). Aqua molecules and N groups are involved in hydrogen bonding and form a three-dimensional network of infinite chains and variable degrees of rings [C3 3(7), R<sup>2</sup> 1(5), R2 2(9), R5 6(22) and R4 6(15)] which deploy along the two crystallographic axes a and b (**Figure 2b** and **c**) [8].

### **4. Luminescent properties**

Photoluminescence spectra were measured using a Cary Eclipse (Agilent Technologies) fluorescence spectrophotometer in a quartz cell (1.1 cm cross section) equipped with a xenon lamp and a dual monochromator. The measurements in solvents of different polarities were carried out at ambient temperature (298 K) with the slit ex/em = 20/10 nm. The photoluminescence properties of {(C12N2H8) H2O} in any solution were investigated in the visible region. The emission spectra of phh (10–<sup>4</sup> M) in non-polar solvents, viz. benzene and toluene, show maximum at 420 nm at λex = 320 nm (**Figure 3**). Studies at higher concentrations of the probe were not possible as it is marginally soluble in non-polar solvents. In polar solvents, viz. methanol, ethanol and acetonitrile, the solution exhibit emission maximum at

