Abstract
The compounds I (Z)-2-(phenyl)-3-(2,4,5-trimethoxyphenyl)acrylonitrile with one side (2,4,5-MeO-), one symmetrical (2Z,2′Z)-2,2′-(1,4-phenylene)bis(3-(2,4,5-trimethoxyphenyl)acrylonitrile), II (both sides with (2,4,5-MeO-), and three positional isomers with pyridine (Z)-2-(pyridin-2- 3, or 4-yl)-3-(2,4,5-trimethoxyphenyl)acrylonitrile, III–V were synthetized and characterized by UV-Vis, fluorescence, IR, H1-NMR, and EI mass spectrometry as well as single crystal X-ray diffraction (SCXRD). The optical properties were strongly influenced by the solvent (hyperchromic and hypochromic shift), which were compared with the solid state. According to the solvatochromism theory, the excited-state (μe) and ground-state (μg) dipole moments were calculated based on the variation of Stokes shift with the solvent’s relative permittivity, refractive index, and polarity parameters. SCXRD analyses revealed that the compounds I and II crystallized in the monoclinic system with the space group, P21/n and P21/c, respectively, and with Z = 4 and 2. III, IV, and V crystallized in space groups: orthorhombic, Pbca; triclinic, P-1; and monoclinic, P21 with Z = 1, 2, and 2, respectively. The intermolecular interactions for compounds I–V were investigated using the CCDC Mercury software and their energies were quantified using PIXEL. The density of states (DOS), molecular electrostatic potential surfaces (MEPS), and natural bond orbitals (NBO) of the compounds were determined to evaluate the photophysical properties.
Highlights
Solid state materials whose optical properties are susceptible to changes by external stimuli are of ongoing interest because they are used in optical information storage, fluorescent switches, memory devices, and optoelectronic devices [1,2]
Comparing the frontier molecular orbitals (FMO) energy values of the acrylonitrile derivatives, I–V containing 2,4,5-TMeO- with reported compounds [46,47,48,49,50,67] substituted with F, Cl, Br, -N(CH3)2, -N(Ph)2, -Cz, chalcones, and ring phenyl ring or pyridine ring in ortho, meta and para positions, we found that energy of the lowest unoccupied molecular orbital (ELUMO) values indicated I–V are better electron acceptors than electron donors (Figure 5 and Figure S14) and are able to interact with solvents because the HOMO and LUMO values are very close
This result may indicate that molecules I, III–V preferentially engage in dispersion-type intermolecular interactions. It reinforces the importance of intermolecular interactions. These observations reinforce the fact that the molecules of II, despite having a fundamental dipole moment of approximately zero, do not suffer the same solvent effects as compounds I, III–V
Summary
Solid state materials whose optical properties are susceptible to changes by external stimuli (mechanical forces, solvent, acid vapors, heat and light) are of ongoing interest because they are used in optical information storage, fluorescent switches, memory devices, and optoelectronic devices [1,2]. The molecular arrangement and the intermolecular interactions in the solid state, as well as with the solvent in solution, are important parameters to correlate with their optical properties [6,7]. We performed density of states (DOS), molecular electrostatic potential surfaces (MEPS), and natural bond orbital (NBO) analyses of the compounds to evaluate the effect of the substituents on the optical properties as well as the effects of intermolecular and other interactions on the charge transfer. Free rotation is restricted in compound II, so it is possible that free rotation as a function of solvent causes the observed hypochromic and hyperchromic effects, while the bathochromic shift is the result of the presence of the extended conjugation in the molecule. The change in the position of the absorption maxima is due to conjugation [38]
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