RETRACTED: Structural, morphological and optical analysis related to the origin of the green and red emission band in a chiral Schiff base

Abstract

The structural, morphological and optical properties of an enantiopure Schiff base, namely [(S)-(+)-[(1-naphthyl)-N-(1-benzo[b]tiophen-2-yl)methylidene]ethylamine] (Bt-Naph) are reported. By using Scanning Electron Microscopy (SEM), tubular crystals of different sizes can be seen. X-ray diffraction studies showed an orthorhombic phase, which has been confirmed by powder X-ray diffraction (XRD) analysis applying Bragg's law. The absorbance results showed typical bands of organic molecules located in the UV region for π→π* and n→π* electronic transitions. Considering the behavior of this organic crystal as similar to other crystalline materials, the Tauc law was applied to investigate the band gap energy (Eg). Two electronic transitions were experimentally evaluated: Eg ∼3.5 eV and Eg ∼4.7 eV. The photoluminescence spectroscopy showed a broad emission band located in the visible region at ∼575 nm, identified as a green emission (GE) band. Deconvolution of the spectra displayed two emission bands located at ∼558 nm and ∼672 nm, and the latter was assigned to a yellow emission band. Finally, the Raman spectroscopy exhibited peaks associated with different vibrational modes, typical of molecules containing aromatic rings.