Contents lists available at ScienceDirect Optical Materials journal homepage: www.elsevier.com/locate/optmat Green emission band induced by crystal defects in halogenated (-Br, -Cl, -F) chiral imines with a benzo[b]thiophene-based moiety B. Anzaldo Olivares a , O. Portillo Moreno a,* , G. Hernández Téllez a , E. Rubio Rosas b , F.J. Meléndez Bustamante c , M.E. Castro Sánchez c , P. Sharma d , A. Mendoza a , R. Gutiérrez Pérez a,** a Lab. Síntesis de Complejos. Fac. Cs. Químicas., Universidad Autónoma de Puebla, Edif. FCQ-6, C.U. Av. San Claudio y 22 Sur, Col. San Manuel, C.P. 72592, Puebla, Pue, Mexico b Centro Universitario de Vinculación, Universidad Autónoma de Puebla, C.P. 72570, Puebla, Pue, 72001, Mexico c Lab. Química Teórica, Dpto. Fisicoquímica, Fac. Cs. Quím., Universidad Autónoma de Puebla, Edif. FCQ-10, Av. San Claudio y 22 Sur, Col. San Manuel, C.P. 72570, Puebla, Pue, Mexico d Instituto de Química-UNAM, Cd. Universitaria, C.P. 04510, Cd. México, Mexico ARTICLE INFO Keywords: Photoluminescence Chiral imines Halogen efect Crystal growth Band gap ABSTRACT Four diferent chiral imines were analyzed in solid state, by changing systematically the halogen atom –X (-F, -Cl and -Br) in the para-position of the benzene ring in the chiral moiety of benzo[b]thiophene-based imine com- pounds. The molecular packings showed a signifcant distortion induced by the efect of the stereogenic carbon atoms and the corresponding halogen atom, resulting in nonplanar angular-shaped small molecules. Morphological studies by Scanning Electron Microscopy (SEM) were performed and changes in aspect and shape of the crystals can be clearly seen. The absorbance was registered in the UV-region (~200–400 nm), and showed typical transitions that are commonly displayed in organic molecules with π→π * and n→π* electronic transi- tions. The band gap was quantifed by the Tauc model, and four electronic transitions were found, associated with those observed in experimental results by absorbance, located in the ~3.34–5.86 eV range. By X-ray dif- fraction (XRD) studies, a monoclinic→orthorhombic variation in the crystals was observed. Photoluminescence (PL) signals were examined in the Vis-region at room temperature and a green emission (GE) band located in the ~450–750 nm range was observed, which was associated with crystalline defects and the existing chromo- phores. Likewise, a PL signal located in the ~526–583 nm (~2.35–2.12 eV) range showing the shift of the green- yellow emission was noted. By using Raman spectroscopy, the vibrational modes displayed in these crystals were analyzed. A theoretical support of HOMO-LUMO analysis for these organic crystals is also reported. 1. Introduction In the last three decades, a lot of research has been carried out into organic molecules (OM) regarding their morphological, structural and optical properties for potential application as base materials in the construction of optoelectronic devices and organic lasers [1]. In parti- cular, OM with emission colors in the Vis-region varying from blue [2] and green to red have received a great deal of attention for their uti- lization in light emitting diodes [3,4], as well as a wide range of ap- plications [5]. However, detailed and deep analysis are always needed and by computational theoretical calculations applying diferent models it is possible to perform a detailed examination and predict physical-chemical properties in these OM [6]. Most OM present dif- ferent molecular structures generating diferent molecular packings with the concomitant changes of the crystalline surface morphology as well as the diferent efects generated by electrostatic interactions of short, medium and short range [8] among other important physical properties [7], and as such, all these facts by which absorbance and obviously the emission optical signals can display variations. The aforementioned properties are generally associated with molecular structures generating signifcant changes in refectivity, refractive index, dielectric constant, etc. [9]. Some OM in solid state are known to have high Photoluminescence (PL) signals in the Vis-region, in parti- cular the green emission (GE) band associated with optical and https://doi.org/10.1016/j.optmat.2019.06.007 Received 15 January 2019; Received in revised form 8 April 2019; Accepted 6 June 2019 * Corresponding author. ** Corresponding author. E-mail addresses: osporti@yahoo.com.mx (O.P. Moreno), jrgutie@correo.buap.mx (R.G. Pérez). Optical Materials 94 (2019) 337–347 0925-3467/ © 2019 Elsevier B.V. All rights reserved. T