Methoxy substituent facilitated wide solvatofluorochromism, white light emission, polymorphism and stimuli-responsive fluorescence switching in donor-π-acceptor

Introducing methoxy substituent into triphenylamine-acetophenone based donor-π-acceptor fluorophore, 3-(4-(diphenylamino)phenyl)-1-phenylprop-2-en-1-one (1), produced strong solvatofluorochromism including white light emission, fluorescent polymorphs and mechano-responsive fluorescence switching. The unsubstituted and methoxy substituted compounds displayed strong solvent polarity mediated tunable emission in the solution. Interestingly, 3-(4-(diphenylamino)phenyl)-1-(4-methoxyphenyl)prop-2-en-1-one (2) and 3-(4-(diphenylamino)-2-methoxyphenyl)-1-(4-methoxyphenyl)prop-2-en-1-one (3) showed single molecule white light emission in DMSO and ethanol, respectively. 1-3 exhibited strong green/yellow fluorescence in the solid-state (Quantum yield (Φ_f) = 10 to 23%). 2 produced fluorescent polymorphs (green (2-G) and yellow (2-Y). Single crystal structural analysis revealed that donor and acceptor phenyl units adopted coplanar conformation in 2-G and 3 whereas twisted molecular conformation in 1 and 2-Y. Further, 2-G exhibited π…π interactions facilitated isolated dimers whereas 2-Y showed well separated molecules in the crystal lattice. Aggregation induced emission (AIE) studies showed morphological transformation induced fluorescence tuning for 2. The intramolecular charge transfer (ICT) from TPA to acetophenone was confirmed by computational studies. Mechanofluorochromic (MFC) studies of 1 showed only slight reduction of intensity without modulating fluorescence wavelength significantly but 2 and 3 exhibited visible emissive colour change from yellow to green and vice versa by crushing and heating. Both 2 and 3 also exhibited self-reversible fluorescence switching that was confirmed by PXRD pattern. Thus, methoxy group introduction resulted in obtaining white light emitting fluorescence molecules in the solution state and self-reversible fluorescence switching materials.

Solution and Solid-State Photophysical Properties of Positional Isomeric Acrylonitrile Derivatives with Core Pyridine and Phenyl Moieties: Experimental and DFT Studies

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.

One- and Two-Component Organogels Containing Cyanostilbene without any Auxiliary Substituents

Pyridyl acrylonitrile without traditional auxiliary groups form stable organogels in ethanol. The addition of a second non-gelating cyanostilbene component results in a more stable two-component gel. Single crystal X-ray data reveal the influence of C-H⋅ ⋅ ⋅N, C-H⋅ ⋅ ⋅π, and π-π interactions in the formation of organogels. The morphology of the xerogels was studied by using SEM, which showed the self-assembly of molecules to fibers and sheet-like structures, and phase differences upon the gel formation and the structural phase characterization was measured using powder XRD. Exposure of the organogels to acidic (TFA) vapors results in distinct color changes and loss of gelation properties, thus highlighting the potential of these gels in sensing. The results represent a rare example of two-component organogels using two different cyanostilbene units and show that functional two-component organogels can be formed by utilizing the synergistic effects of the individual components.

Perturbing the AIEE activity of pyridine functionalized α-cyanostilbenes with donor substitutions: an experimental and DFT study

Aggregation propensity of pyridyl functionalized α-cyanostilbenes has been investigated with respect to various amino donors.

Qu-anti-tative analysis of weak non-covalent inter-actions in (Z)-3-(4-chloro-phen-yl)-2-phenyl-acrylo-nitrile: insights from PIXEL and Hirshfeld surface analysis

In the solid state, the title compound, C15H10ClN, is disordered over two orientations with a refined occupancy ratio of 0.86 (2):0.14 (2). The crystal structure is mainly stabilized by inter-molecular C-H⋯N and C-H⋯Cl hydrogen bonds, and C-H⋯π inter-actions. The mol-ecules pack in columns and adjacent columns are linked by weak C-H⋯Cl inter-actions. The PIXEL energy analysis suggests that the inter-molecular C-H⋯π inter-actions form a strong dimer in the major component. Hirshfeld analysis reveals that H⋯C, H⋯H, H⋯Cl and H⋯N contacts are the most important contributors to the crystal packing.

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

Experimental and theoretical insights into the nature of intermolecular interactions and their effect on optical properties of 1-allyl-4-(1-cyano-2-(4-dialkylaminophenyl)vinyl)pyridin-1-ium bromide salts (I and II) are reported. A comparison of optical properties in solution and in the solid-state of the salts (I and II) with their precursors (Ia and IIa) is made. The experimental absorption maxima (λmax) in CHCl3 is at 528 nm for I and at 542 nm for II, and a strong bathochromic shift of ∼110 nm is observed for salts I and II compared with their precursors. The absorption bands in solid-state at ∼627 nm for I and at ∼615 nm for II that are assigned to charge transfer (CT) effect. The optical properties and single crystal structural features of I and II are explored by experimental and computational tools. The calculated λmax and the CT are in good agreement with the experimental results. The intermolecular interactions existing in the crystal structures and their energies are quantified for various dimers by PIXEL, QTAIM and DFT approaches. Three types of interactions, (i) the cation⋅⋅⋅cation interactions, (ii) cation⋅⋅⋅anion interactions and (iii) anion⋅⋅⋅anion interactions are observed. The cationic moiety is mainly destabilized by C-H⋅⋅⋅N/π and π⋅⋅⋅π interactions whereas the cation and anion moiety is predominantly stabilized by strong C-H⋅⋅⋅Br- interactions in both structures. The existence of charge transfer between cation and anion moieties in these structures is established through NBO analysis.

Quantitative analysis of weak non-covalent interactions in (Z)-3-(4-halophenyl)-2-(pyridin-2/3/4-yl)acrylonitriles

A detailed experimental and theoretical investigation on the intermolecular interactions in (Z)-3-(4-halophenyl)-2-(pyridin-2/3/4-yl)acrylonitriles is reported and different π staking motifs observed in these structures.

Dimesitylboryl-functionalised cyanostilbene derivatives of phenothiazine: distinctive polymorphism-dependent emission and mechanofluorochromism

Dimesitylborane-functionalized cyanostilbene derivatives of phenothiazine exhibit polymorphism with distinct solid-state emissions.