*3.3.2 Photo-physical properties of the synthesized DBrcN and DOMCN*

Optical properties of the synthesized oligomer were investigated essentially with steady-state optical absorption and photoluminescence spectroscopies in a dilute solution state. Optical absorption and photoluminescence spectra are presented in **Figure 6**. Both synthesized molecules absorb in the UV and in the near-visible part. A wide absorption is detected at 250 nm and a large band absorption centered at around 360 nm and 380 nm respectively for DBrCN and DOMCN synthesized molecules, and are assigned to π-π\* optical transition. From optical absorption spectra, optical band gap Eg is estimated from the onset of absorption, which is estimated to be 3 eV and 2.8 eV respectively for DBrCN and DOMCN molecules.

**Figure 6.**

*(a) Optical absorption and (b) photoluminescence spectra (excitation 370 nm) of the DOMCN and DBrCN synthesized molecules recorded in chloroform solution.*

*Synthesis, Experimental and Theoretical Investigations on the Optical and Electronic Properties… DOI: http://dx.doi.org/10.5772/intechopen.103807*

**Figure 8.** *C.I.E cartographic of the investigated organic material.*

Under 370 nm line excitation a narrow blue emission is observed for the two materials. A change in the shape of the PL spectrum of the molecule is observed going from DBrCN and DOMCN. A vibronic spectrum with two maxima at 443 and 460 nm for DBrCN is obtained. Theoretical computations using the DFT-B3Lyp-6- 31G(d) level of theory were undertaken in order to estimate the electronic parameter. **Figure 7** presents the optimized chemical structure of the investigated molecule at the ground state and the contour plot HOMO and LUMO obtained with 0.02 isovalue using GAUSSVIEW software [27].

Electronic parameters deduced from the ground state optimized chemical structure of the two compounds and the synthesized PVK-MeT are summarized in **Table 1**.

From CIE cartography (**Figure 8**), it is clearly seen the effect of the use of Poly(N\_vinylcarbazole) (PVK) on the chemical polymerization of 3-methylthiophene monomers. From PMeT to PVK-MeT a decrease of x value from 0.5 for single PMET to 0.38 for PVK-MET resulted in a green-yellow color emission. Meanwhile, the synthesized small molecule DOMCN and DBrCN present a blue emission, which permits the use as an emissive layer for the blue light-emitting diode.
