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.

We report an interesting and clear property–structure relationship between the emission wavelength and the morphologies of samples separated by evaporation using a sublimator and a solvent. The compounds are (Z)-3-(4-(dimethylamino)phenyl)-2-(pyridin-4-yl)acrylonitrile Z-DMPyACN (I) and (Z)-3-(4-(diphenylamino)phenyl)-2-(pyridin-2-yl)acrylonitrile Z-DPPyACN (II). I exhibits strong emission in the solid state, but not in a solution, whereas II exhibits emission in a solution and as a solid. Characterization by single-crystal X-ray crystallography showed that the Z-DMPyACN polymorph (Ii) has a monoclinic unit cell with a = 7.0445(2); b = 17.1474(5); c = 10.9776(4) Å, and β = 107.251(4)° and is found in the space group P2₁/c with Z′ = 1. The orange crystal habit and color are different from the structure reported, (Z′ = 2, block and yellow). The Ii luminescence displayed an absorbance maximum at λ_max = 427 nm and an emission maximum at λ_em = 555 nm. From the Z-DPPyACN II evaporation in the sublimator, three solids were recovered, featuring emission wavelengths that were dependent on the size of the particles (nanoparticles) rather than on the single-crystal structure. The IIg, IIy, and IIo powders showed emission maxima at λ_em = 546, 558, and 607 nm, respectively. Characterization was carried out by UV-vis, fluorescence and ¹H-NMR in different polarity solvents, as well as SCXRD, PXRD and SEM.