Conformational and Molecular Structures of α,β-Unsaturated Acrylonitrile Derivatives: Photophysical Properties and Their Frontier Orbitals

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.

Preferential Orientation of Crystals and its Influence on the Emission Wavelength of Acrylonitrile Derivatives Treated with Polar Solvents

“…The one photon absorption spectra in the UV spectra of each pair of crystals (yellow and orange) dissolved in CHCl 3 or in CH 2 Cl 2 showed two absorption bands: one at λ max 296–301 nm, corresponding to the n→π* transition due to electron transfer from the amine moieties and a second absorption band with λ max at 416–427 nm, which is assigned to π–π* transition of the conjugated double bond . The presence of the substituents, either the N(CH 3 ) 2 or ‐N(Ph) 2 group, increased the intensity of the bands assigned to n→π*, which corresponded to the extended delocalization of the nitrogen pair onto the additional two phenyl groups from ‐N(Ph) 2 than ‐N(CH 3 ) 2 , that transferred to the whole molecule …”

“…Table includes a list of selected bond lengths and torsion angles for III–V . The p ‐diphenylamino substituent prevents a delocalization on the central part of the molecular structure formed by the phenyl ring attached to the acrylonitrile moiety, and consequently, the molecular packing is disturbed by intermolecular interaction. The double bond lengths of C(19)–C(20) [1.352(2) for III , 1.351(2) and 1.352(2) for IV , 1.351(2) for V ] are identical in all three structures.…”

“…The contact distances between molecules can be affected by any, all, or none of these three strains ( Figure ). The conformer A has been typically found in different isomeric compounds that have been crystallized . The IV torsion angles between molecules A and B have values that are closer, within the standard uncertainties (Table S2, Supporting Information), indicating that crystal packing between A and B conferred a twist on the acrylonitrile group, making the phenylacrylonitrile moiety almost planar.…”

Experimental and Theoretical Insights into the Optical Properties and Intermolecular Interactions in Push‐Pull Bromide Salts

“…The asymmetric unit of polymorph‐1 contains two crystallographically independent molecules, whereas, polymorph‐2 contains one molecule in the asymmetric unit. Compound IIa crystallized in the orthorhombic Pbcn space group (refcode: AWEGEQ) with one molecule in the asymmetric unit . In order to understand the effect of quaternization of the pyridine nitrogen atom in I–II , a detailed structural comparison of I–II and their precursor structures ( Ia–IIa ),, has been performed.…”

“…As shown in Scheme , the compound ( Z )‐3‐(4‐(dimethylamino)phenyl)‐2‐(pyridin‐4‐yl)‐acrylonitrile ( Ia ) and ( Z )‐3‐(4‐(diphenylamino)phenyl)‐2‐(pyridin‐4‐yl)acrylonitrile ( IIa ) were synthesized from 4‐ N,N ‐substituted aminobenzldehyde ( Ib–IIb ) and 4‐(cyanomethyl)pyridin‐1‐ium chloride( 2 ) as reported earlier ,, . The mixture of Ia or IIa (1 mmol) and allyl bromide ( 3 , 1.1 mmol) in 25 mL of acetone were refluxed for 12 h. Upon completion of the reaction, the reaction mixture was cooldown to room temperature and the salts ( I–II ) were settled as precipitates.…”