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Molecules. 2019 Sep 11;24(18). pii: E3304. doi: 10.3390/molecules24183304.

Experimental and DFT Study of the Photoluminescent Green Emission Band of Halogenated (-F, -Cl, and -Br) Imines.

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Laboratorio de Química Teórica, Centro de Investigación, Dpto. de Fisicoquímica, Facultad de Ciencias Químicas, Universidad Autónoma de Puebla, Edif. FCQ10, San Claudio y 22 Sur, Ciudad Universitaria, Col. San Manuel, Puebla, Puebla 72570, Mexico.
Centro de Química, Instituto de Ciencias, Universidad Autónoma de Puebla, Complejo de Ciencias, ICUAP, Edif. IC8, 22 Sur y San Claudio, Ciudad Universitaria, Puebla 72570, Mexico.
Laboratorio de Síntesis de Complejos. Fac. Ciencias. Químicas, Universidad Autónoma de Puebla, P.O. Box 156, C.P. Puebla Pue 72001, Mexico.
Posgrado en Optoelectrónica, Facultad de Ciencias Físico-Matemáticas, Universidad Autónoma de Puebla, Pue., P.O. Box 1067, C.P. Puebla Pue 72001, Mexico.
Centro Universitario de Vinculación y Transferencia Tecnológica, Universidad Autónoma de Puebla, C.U., C.P. Puebla Pue 72001, Mexico.


The morphological, optical, and structural changes in crystalline chiral imines derived from 2-naphthaldehyde as a result of changing the -F, -Cl, and -Br halogen (-X) atoms are reported. Scanning electron microscopy (SEM), optical absorption, photoluminescence (PL), and powder X-ray diffraction (XRD) studies were performed. Theoretical results of optical and structural properties were calculated using the PBE1PBE hybrid functional and compared with the experimental results. Differences in surface morphology, absorbance, XRD, and PL of crystals were due to the change of halogen atoms in the chiral moiety of the imine. Absorption spectra exhibited the typical bands of the naphthalene chromophore located in the ~200-350 nm range. Observed absorption bands in the UV region are associated with π→π* and n→π* electronic transitions. The band gap energy was calculated using the Tauc model. It showed a shift in the ~3.5-4.5 eV range and the crystals exhibited different electronic transitions associated with the results of absorbance in the UV region. XRD showed the monoclinic→orthorhombic crystalline phase transition. PL spectra displayed broad bands in the visible region and all the samples have an emission band (identified as a green emission band) in the ~400-750 nm range. This was associated with defects produced in the morphology, molecular packing, inductive effect and polarizability, crystalline phase transition, and increase in size of the corresponding halogen atoms; i.e., changes presumably induced by -C-XX-, -C-XN-, -C-Nπ, and -C-Xπ interactions in these crystalline materials were associated with morphological, optical, and structural changes.


DFT calculations; band gap energy; green emission band; halogen effect; photoluminescence

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