Optical and dielectrical properties of azo quinoline thin films

•A novel series of quinoline azodyes (AQLn) were investigated.•The emission spectra of quinoline azodyes exhibit dual fluorescence peaks in the region 512–580 nm.•The optical transitions are found to be indirect allowed.•The values of Eo and Ed are found to be in the range of 2.41–5.84 eV and 4.72–9.16 eV depending on the substituent group.•Correlated barrier hopping is the dominant conduction mechanism of quinoline azodyes (AQLn).

In this study, the optical and dielectrical properties of a novel series of quinoline azodyes (5-(4′-derivatives phenyl azo)-8-hydroxy-7-quinolinecarboxaldehyde) (AQL1–AQL5) were investigated and the obtained results were analyzed. The X-ray diffraction (XRD) patterns of AQLn show that the materials in the powder form are a mixture of amorphous and crystalline structure, while the thermally deposited thin films are completely amorphous. The optical constants such as the refractive index, n, the absorption index, k and the absorption coefficient, α, were determined using spectrophotometric measurements of transmittance (T) and reflectance (R) in the wavelength range 200–2500 nm. According to the single oscillator model (SOM), some related parameters such as oscillation energy (Eo), the dispersion energy (Ed), the optical dielectric constant (ε∞), the lattice dielectric constant (εL) and the ratio of free carrier concentration to its effective mass (N/m*) are estimated. The emission spectra of azo quinoline ligands (AQLn) exhibit dual fluorescence peaks in the region 512–580 nm. This finding reveals the formation of two stoichiometric hydrogen-bonding in the ground and excited state. The dielectrical properties and alternating current conductivity (σAC) are investigated in temperature range 298–483 K and frequency range 0.1–100 KHz.

Graphical abstractFluorescence emission spectra of thermally evaporated thin film of AQLn at λex = 365 nm.Figure optionsDownload full-size imageDownload as PowerPoint slide