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. 2022 Jan 22;27(3):721.
doi: 10.3390/molecules27030721.

The Structural and Optical Properties of 1,2,4-Triazolo[4,3- a]pyridine-3-amine

Lucyna Dymińska  1 , Jerzy Hanuza  2 , Jan Janczak  2 , Maciej Ptak  2 , Radosław Lisiecki  2
Affiliations

The Structural and Optical Properties of 1,2,4-Triazolo[4,3- a]pyridine-3-amine

Lucyna Dymińska et al. Molecules. .

Abstract

The structural and spectroscopic properties of a new triazolopyridine derivative (1,2,4-triazolo[4,3-a]pyridin-3-amine) are described in this paper. Its FTIR spectrum was recorded in the 100-4000 cm-1 range and its FT-Raman spectrum in the range 80-4000 cm-1. The molecular structure and vibrational spectra were analyzed using the B3LYP/6-311G(2d,2p) approach and the GAUSSIAN 16W program. The assignment of the observed bands to the respective normal modes was proposed on the basis of PED calculations. XRD studies revealed that the studied compound crystallizes in the centrosymmetric monoclinic space group P21/n with eight molecules per unit cell. However, the asymmetric unit contains two 1,2,4-triazolo[4,3-a]pyridin-3-amine molecules linked via N-H⋯N hydrogen bonds with a R22(8) graph. The stability of the studied molecule was considered using NBO analysis. Electron absorption and the luminescence spectra were measured and discussed in terms of the calculated singlet, triplet, HOMO and LUMO electron energies. The Stokes shifts derived from the optical spectra were equal to 9410 cm-1 for the triazole ring and 7625 cm-1 for the pyridine ring.

Keywords: 1,2,4-triazolo[4,3-a]pyridin-3-amine; XRD studies; molecular structure; spectroscopic analysis.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Experimental (a) and simulated (b) from an X-ray structural analysis on a single crystal for TPa-NH2.
Figure 2
Figure 2
View of the asymmetric unit of TPa-NH2 with the labeling scheme. Displacement ellipsoids are shown at the 50% probability level, H atoms with arbitrary radii.
Figure 3
Figure 3
Crystal packing of the TPa-NH2 molecules in the unit cell showing the N–H⋯N hydrogen-bonded dimers with an R22(8) graph viewed almost along [100] (a) and [210] directions (b).
Figure 4
Figure 4
Molecular structure of TPa-NH2 with numbering atoms.
Figure 5
Figure 5
Infrared spectrum of TPa-NH2.
Figure 6
Figure 6
Raman spectrum of TPa-NH2.
Figure 7
Figure 7
Comparison of the experimental and calculated infrared and Raman spectra of TPa-NH2.
Figure 8
Figure 8
The electron absorption spectrum of the TPa-NH2 molecule.
Figure 9
Figure 9
HOMO and LUMO molecular orbitals for the TPa-NH2 monomer and dimer.
Figure 9
Figure 9
HOMO and LUMO molecular orbitals for the TPa-NH2 monomer and dimer.
Figure 10
Figure 10
The emission spectrum of the TPa-NH2 molecule. Inserts show the emission lifetime for the TPa-NH2 molecule excited at 321 nm.
Figure 11
Figure 11
Depopulation mechanism of the excited states proposed for the studied 1,2,4-triazolo[4,3-a]pyridin-3-amine.
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