A Spectral , Optical , Microscopic Study , Synthesis and Characterization of PVC Films Containing Schiff Base Complexes

In this work, synthesis of conducting polymeric films namely, PVC thin films was carried out containing Schiff base (L) with Cu 2+ , Cr 3+ , Ni 2+ , Co 2+ , in addition to inspecting the possibilities of measuring energy gap values of PVC-L-M with variety metal ions. These new polymeric films (PVC-L-M) were characterized by FTIR spectrophotometry, energy gap and surface morphology. The optical data recorded that the band gap values are influenced by the type of metals. All modified films have a red shift in optical properties in the ultraviolet region. The PVC-L-Co(II) was the lowest value of the optical band gap, 3.1 eV.


Introduction:
Semiconductor materials with massive range have various features.Utilizing these features makes it reasonable to form e.g.LEDs emitting light through a huge extent of memristor instruments or wavelengths (1).Photon established techniques (reaction measurements or absorption) can provide optical band gap data e.g. by adjust a Tauc plot (2), but probe mostly much thicker layers.Photoemission experiments can be utilized to get band gap data.Here the separation of a sharp core level with the onset of improved intensity of the background can be seen as a band gap fingerprint (see e.g. 3).The electronic and optical behavior of semiconductors is determined by two essential properties namely refractive index and energy gap.Material refractive index is reduced with energy gap and therefore, these two essential quantities of a material are believed to have certain correlation.There were many attempts to discover appropriate relationship, both semi empirical and empirical, between the refractive index and semiconductors energy gap (4,5,6,7).
The physiological importance of oxygen donor in the organic compounds increasing the active role acted by coordinating certain metal ions to utilize in studying the structural aspects and synthesizing metal complexes with some sulphur, nitrogen and oxygen donor ligands (8)(9)(10).The aim of this work is to study transition metals influence on the optical, electrical properties and surface morphology of the novel materials.

Instrumentation
A Shimadzu 8400 Spectrophotometer (Shimadzu Cooperation, Kyoto, Japan) was used to record the FTIR spectra (4000-400 cm -1 ) using the KBr disk technique.A Bruker DRX400 NMR Spectrometer (Bruker, Zürich, Switzerland) 400 MHz was utilized to record 1 H-NMR spectra in DMSO-d6 to record the changes in energy gap values for polymeric films measured by diffuse reflectance UV-Vis Spectroscopy.The surface morphology of polymeric films was recorded on Meiji Techno Microscope (Meiji Techno, Tokyo, Japan).

Synthesis of PVC -Ligand
0.05 mole of Schiff base (L) was added to solution of 0.1 g PVC in 20 mL THF, the mixture was refluxed for 3 hours.Hot mixture was cast into petri dish.A white precipitate was formed after refluxing.The modified polymer (PVC-L) film was dried under vacuum Fig. 2.

PVC Films Preparation
PVC solution (0.5% concentration) in THF was used to synthesize 40 µm thickness of polymeric films.The films were prepared by pouring the solution onto a glass plate, left to dry for a day to remove any residual of THF (12)(13)(14).

Results and Discussion: Synthesis and Characterization of Schiff Base L
Schiff base L was synthesized based on literature procedures (11).Reaction of biphenyl-3,3',4,4'-tetraamine and excess of 3hydroxybenzaldehyde (four mole equivalents), in the presence of glacial acetic acid as a catalyst under 4 hours reflux, gave the corresponding Schiff base L in 80% yields (Scheme 1).

Scheme 1. Synthesis of Schiff base L.
The FTIR spectrum of L shows absorption band at 1600 cm -1 that, due to C=N bond, can also denote the absence of NH 2 and C=O groups absorptions which belong to ammine and aldehyde groups, respectively as shown in Fig. 4.

Figure 4. FTIR spectrum of Schiff base L.
Table 1 and Fig. 5 show the nuclear magnetic resonance spectral data for L. It can be seen that the singlet signals that resonate at the 8.01 ppm region are attributed to the azomethine protons.Moreover, the aromatic protons with chemical shifts and expected multiplicity can be noticed (11).

Characterization of PVC films
The modified polymers structure was confirmed by FTIR spectroscopy, energy gap and microscope techniques.The modification of PVC films with various metals were confirmed by FTIR spectroscopy.Table 2 shows vibration bands of C-O, M-O and C-Cl.Furthermore, in PVC-L (the modified polymer) spectrum can record a strong band at ν (694) cm −1 .This band is due to the ν (C-Cl) band which is unlike the unmodified PVC ν (616) cm −1 .

Optical Properties
The effect of metals added to the values of energy gap was shown in Table 3, Fig. 6    The energy gap shift could be assigned to the polarons formation in the doped films (8).The polymer-metal composites may be recognized by interaction of metal with the polar group that exists in polymeric chain.The conductivity measurement for PVC films in the additives existence following this order: PVC-L>PVC-L-Cu>PVC-L-Cr>PVC-L-Ni>PVC-L-Co.The surface morphology of polymeric films was characterized by using microscope, the surface morphology confirms notifications about roughness, irregularity and defects into polymeric materials (9).

Conclusion:
The structure of Schiff base is established on the basis of its FTIR and 1 HNMR spectroscopy.Each modified polymer is investigated by FTIR, diffuse reflectance UV-Vis Spectroscopy and optical microscope.The properties of modified PVC with different metals are investigated.The energy gap method is used to determine these properties, the energy gap values decreased as order: PVC-L > PVC-L-Cu > PVC-L-Cr > PVC-L-Ni > PVC-L-Co.

Film
and 7.The values of energy gap are decreased in the trend pure PVC-L, PVC-L-Cu, PVC-L-Cr, PVC-L-Ni and PVC-L-Co.

Figure 7 .
Figure 7. (αhυ) 2 with photon energy for PVC-L-Cu.The energy gap shift could be assigned to the polarons formation in the doped films(8).The polymer-metal composites may be recognized by interaction of metal with the polar group that exists in polymeric chain.The conductivity measurement for PVC films in the additives existence following this order: PVC-L>PVC-L-Cu>PVC-L-Cr>PVC-L- Photon Energy (eV)