Two Different Emissions of (2Z)-2-(4-Bromophenyl)-3-[4-(dimethylamino)phenyl]prop-2-enenitrile Due to Crystal Habit and Size: Synthesis, Optical, and Supramolecular Characterization

Abstract

Optical and X-ray diffraction characterizations of crystals I and II of (2Z)-2-(4-bromophenyl)-3-[4-(dimethylamino)phenyl]prop-2-enenitrile (Z-4-BrPhDMAPhACN) are reported. I and II belong to the same monoclinic space group and have nearly identical unit-cell dimensions [I: a = 11.0169(2); b = 6.02041(11); c = 21.8541(4); (β) 98.4082(18). II: a = 11.0475(6); b = 6.0273(3); c = 21.8533(11); (β) 98.315(5)]. Crystals I and II were formed under different conditions and have different crystal habits and colors: crystals I are yellow blocks, whereas crystals II are small, orange needles.I and II show absorption maxima (λ abs ) in solution at 404 nm and emission (λ em ) maxima at 501 nm (I) and at 502 nm (II). However, their emission maxima are different in the solid state: I shows an emission at 512 nm and a shoulder at 534 nm, whereas II exhibits a λ em maximum at 582 nm. The differences in solid-state photoluminescence were attributed to variations in the crystal morphology and to the crystal habit and size. Both I and II were characterized by nuclear magnetic resonance, mass spectrometry, infrared spectroscopy, UV−vis spectroscopy, fluorescence, cyclic voltammetry, single-crystal and powder X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, and density functional theory calculations.

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

“…Rather, the aromatic rings must show a strong edge‐to‐face interaction through their vertices. Compounds I and II , as well as other recently reported structures showed enhanced fluorescence in the aggregated or solid state, however, the enhanced fluorescence could not arise from movement through the rings . In our structures, III–V, the crystal structure analysis indicated that these compounds do not present the intramolecular π–π interactions and they did not exhibit quenching.…”

“…We propose that due to the intermolecular interaction, the molecules become more rigid, and then enhance the fluorescence; the interaction must be strong through the vertices rings. Our results can also explain the aggregation effect on fluorescence …”

“…Recently we have reported the interesting structure of ( Z )‐2‐(4‐bromophenyl)‐3‐(4‐(dimethylamino)phenyl)acrylonitrile, which crystallizes in two different crystal habits: yellow blocks and orange needles. X‐ray structure showed that both crystals are ordered and identical (i.e., same unit‐cell parameters, Z number, crystal system, and space group).…”

“…These compounds differ in the emission in the solid state as compared with the emission from the solution. Our goal was to comprehend the cause of the differences in emission for Z‐2‐(4‐bromophenyl)‐3‐(4‐dimethylaminophenyl)acrylonitrile in solid state and in solution . We describe the study of five compounds ( I–V , see Scheme ) selected according to dyes families to compare plane‐to‐plane stacking versus to face‐to‐edge.…”

“…Precipitation occurs, which can lead to microcrystal dispersion . It has been shown that several factors influence the size and morphology of the microcrystals …”