Abstract
We report single crystal X-ray diffraction (hereafter, SCXRD) analyses of derivatives featuring the electron-donor N-ethylcarbazole or the (4-diphenylamino)phenyl moieties associated with a -CN group attached to a double bond. The compounds are (2Z)-3-(4-(diphenylamino)-phenyl)-2-(pyridin-3-yl)prop-2-enenitrile (I), (2Z)-3-(4-(diphenylamino)phenyl)-2-(pyridin-4-yl)-prop-2-enenitrile (II) and (2Z)-3-(9-ethyl-9H-carbazol-3-yl)-2-(pyridin-2-yl)enenitrile (III). SCXRD analyses reveal that I and III crystallize in the monoclinic space groups P2/c with Z’ = 2 and C2/c with Z’ = 1, respectively. Compound II crystallized in the orthorhombic space group Pbcn with Z’ = 1. The molecular packing analysis was conducted to examine the pyridine core effect, depending on the ortho, meta- and para-positions of the nitrogen atom, with respect to the optical properties and number of independent molecules (Z’). It is found that the double bond bearing a diphenylamino moiety introduced properties to exhibit a strong π-π-interaction in the solid state. The compounds were examined to evaluate the effects of solvent polarity, the role of the molecular structure, and the molecular interactions on their self-assembly behaviors. Compound I crystallized with a cell with two conformers, anti and syn, due to interaction with solvent. DFT calculations indicated the anti and syn structures of I are energetically stable (less than 1 eV). Also electrochemical and photophysical properties of the compounds were investigated, as well as the determination of optimization calculations in gas and different solvent (chloroform, cyclohexane, methanol, ethanol, tetrahydrofuran, dichloromethane and dimethyl sulfoxide) in the Gaussian09 program. The effect of solvent by PCM method was also investigated. The frontier HOMO and LUMO energies and gap energies are reported.
Highlights
The study of π-conjugated organic compounds has led to the development of a rich variety of new concepts based on the interplay between their π-electronic structures and their molecularMolecules 2016, 21, 389; doi:10.3390/molecules21040389 www.mdpi.com/journal/moleculesMolecules 2016, 21, 389 structures
We have focused our investigations on the synthesis of different α,β-unsaturated acrylonitrile with different derivatives functionalized with electron donors such as diphenylamino, dimethylamino, and carbazole attached to the conjugated double bond and with electron acceptors such as the CN and the pyridyl core
We reported marked differences in the optical properties of the diphenylamino versus dimethylamine groups, in their fluorescence behaviors, which we compared in the solid state, in single crystals, and in solution in different solvents [28,29]
Summary
We reported marked differences in the optical properties of the diphenylamino versus dimethylamine groups, in their fluorescence behaviors, which we compared in the solid state, in single crystals, and in solution in different solvents [28,29]. Several research groups have reported [25,26] that in the absence of electrostatic repulsion, organic molecules can be exactly superimposed on top of one another in a perfect co-facial situation, and usually any displacements can occur along the shortest/longest molecular axes between adjacent molecules These theoretical investigations show that such displacements could strongly affect the intermolecular electronic couplings, in a way that depends on the bonding-antibonding pattern of the frontier molecular orbitals (HOMO, highest occupied molecular orbital, or LUMO, lowest unoccupied molecular orbital) [39]. Structures and μ (dipole moment, Debyes) calculated in gas phase at M06L/cc-pVDZ theory level (ii)
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