Presence Of Charge-transfer Interaction Research Articles

Investigation of the structure and multi-stimuli-responsive behavior of ion-associated salt solvates of binary crystals

Investigation of the intermolecular interactions and crystal packing to understand crystal growth is a prime objective of crystal engineering. Solvent molecules within crystal assist the supramolecular aggregation, however, control over their lattice incorporation remains uncertain. In this work, we report three solvates of an ionic organic salt of a diazo-naphthol sulfonate (1) and 1,10-phenanthroline with one (2), three (3) and four (4) lattice water molecules. Attempts to isolate the dihydrate form were unsuccessful, while the monohydrate of 1 has been crystallised for comparative structural investigations. Structural studies reveal the existence of intriguing sulfonate-diazo intermolecular interactions responsible for centrosymmetric dimerization of the organosulfonate 1, which also persist in 2–4, validating higher preference and robustness of the synthon. Repetitive aggregation of the sulfonate-diazo interaction in 1 leads to the formation of linear π-stacked aggregate, which further aggregates through the lattice water molecules. The structural comparison indicates the preferential formation of the organo-sulfonate dimers in hydrated salts 2–4. Further, sandwich tetramers in 2 and 4 are formed by charge transfer interaction of the organo-sulfonate dimers with pyridinium coformer on either side, which are further associated by the lattice water molecules into disparately packed 3-dimensional supramolecules. The organo-sulfonates in 3 form a similar type of extended π-stacked chains as in 1, which are flanked by pyridinium ions to form hydrogen-bonded tapes, which are helped by the lattice water molecules to grow as segregated stacked layer solid. The characteristic absorption frequency of the diazo functionality is blue-shifted in infrared spectra of the cocrystal forms, indicating the presence of charge transfer interactions. The presence of dynamic solvent and protons in the lattice makes the solid forms multi-stimuli-responsive to exhibit mechano and vapochromic response. These phenomena have been studied in detail with the help of thermal, spectroscopic, and powder-diffraction studies.

Crystalline triphenylamine-substituted arenes: solid-state packing and luminescence properties

The crystal packing and solid state photophysical properties of twisted propeller-shaped triphenylamine (T) incorporated aromatic hydrocarbons [ArT where Ar = benzene (Ph), naphthalene (N), anthracene (A), phenanthrene (Phe), pyrene (Py) and perylene (Pe)] are investigated. The qualitative crystal structure and quantum theory of atoms-in-molecules (QTAIM) analyses revealed the dominant role of intermolecular C–H⋯C interactions in governing the three-dimensional arrangement in ArT crystals. Hirshfeld surface analyses revealed that the triphenylamine-substituted arene (ArT) crystals possess a herringbone motif with ρ (%C–H⋯C/%C⋯C) values varying from 10.4 in PeT to 101.2 in AT. A blue shift of ca. 10–28 nm in the emission maxima for PhT, NT, AT, PheT and PyT is observed in the solid state in comparison to that in dichloromethane while the solid state emission maxima is red shifted (ca. 25–71 nm) compared to that in hexane. A 2.40-fold enhancement in the quantum yield of AT is observed in the solid state relative to the solution state (dichloromethane). Solvent polarity dependent absorption and emission measurements of ArT derivatives along with Lippert–Mataga analyses evidenced the presence of charge transfer interactions between Ar and T units. A precise and systematic understanding of the influence of the crystal structure on the photophysical properties is quintessential to achieve highly efficient organic light emitting diodes and other optoelectronic devices in the near future.

Crystalline triphenylamine substituted arenes: solid state packing and luminescence properties

The crystal packing and solid state photophysical properties of twisted propeller-shaped triphenylamine (T) incorporated aromatic hydrocarbons [ArT where Ar = benzene (Ph), naphthalene (N), anthracene (A), phenanthrene (Phe), pyrene (Py) and perylene (Pe)] are investigated. The qualitative crystal structure and quantum theory of atoms-in-molecules (QTAIM) analyses revealed the dominant role of intermolecular C–H⋯C interactions in governing the three-dimensional arrangement in ArT crystals. Hirshfeld surface analyses revealed that the triphenylamine-substituted arene (ArT) crystals possess a herringbone motif with ρ (%C–H⋯C/%C⋯C) values varying from 10.4 in PeT to 101.2 in AT. A blue shift of ca. 10–28 nm in the emission maxima for PhT, NT, AT, PheT and PyT is observed in the solid state in comparison to that in dichloromethane while the solid state emission maxima is red shifted (ca. 25–71 nm) compared to that in hexane. A 2.40-fold enhancement in the quantum yield of AT is observed in the solid state relative to the solution state (dichloromethane). Solvent polarity dependent absorption and emission measurements of ArT derivatives along with Lippert–Mataga analyses evidenced the presence of charge transfer interactions between Ar and T units. A precise and systematic understanding of the influence of the crystal structure on the photophysical properties is quintessential to achieve highly efficient organic light emitting diodes and other optoelectronic devices in the near future.

Toward Multifunctional Polymer Hybrid through Tunable Charge Transfer Interaction of Anthracene/Naphthalenediimide

The interaction between building blocks in the polymer hybrids plays an important role in their performance and functions. Herein, a novel multifunctional polymer hybrid with tunable charge transfer (CT) interaction between π‐electron‐poor naphthalenediimide (NDI) containing polyimide (PI) and π‐electron‐rich anthracene (AN) ended polyhedral oligomer silsesquioxane (POSS‐AN) is reported (name the polymer hybrid “PI@POSS‐AN”), in which the presence of CT interaction between NDI and AN and its controllable feature are confirmed by UV−vis and fluorescence spectra. A new absorption band at 500 nm in the visible region appears and the emission maxima of the CT complexes are distinctly red‐shifted to 645 nm, while the fluorescence of NDI (493 nm) and AN (481 nm) are significantly quenched in the polymer hybrids. The resulting hybrid films are transparent and homogeneous, exhibit the enhanced thermal and mechanical performance with the increasing content of POSS‐AN. Thanks to the reversible photodimerization of AN, CT interaction between NDI and AN can be on‐off controlled in situ by UV light and heating, and rewritable fluorescence micro‐patterns with red and green emission can be obtained. In addition, the cross‐linked polymer hybrids possess healability and reprocessing performance.

Highly fluorinated polyimide blends – Insights into physico-chemical characterization

A thorough study on the physico-chemical properties of novel blends of fluorinated aromatic polyimides prepared on the basis of the similarity of dianhydride monomer units was performed. High-temperature solution polycondensation reactions resulted in high molecular weights polyimides further used as blend components. The blend films and coatings were rootedly characterized by various methods, including FTIR, DSC, thermal stability, UV–Vis and fluorescence spectroscopy, with emphasis on the miscibility behaviour. They exhibited high thermal stability and unique glass transition temperature, a critical evidence of the blends homogeneity. The presence of charge transfer interactions between neighbour polyimide chains was comprehended by UV–Vis and fluorescence spectroscopy, and discussed in correlation with chemical structures. The hydrophobic blend films showed a porous structure or an interlamellar or interfibrillar segregated morphology, good mechanical and optical properties with high transparency. Furthermore, new insights into their physico-chemical behaviour induced by the trifluoromethyl group or other structural features are discussed.

Effects of partial charge-transfer solute – solvent interactions in absorption spectra of aromatic hydrocarbons in aqueous and alcoholic solutions

A method for study of charge-transfer interactions between solute molecules and solvent based on the comparison of the ratios of spectral shifts of different electronic transitions in solute molecules in chemically inert solvent is proposed. The method is applicable to molecules that do not change their dipole moment on excitation. As an example, a presence of charge transfer interactions in higher electronic states of aromatic hydrocarbons (benzene, phenanthrene, and naphthalene) dissolved in water and alcohols was demonstrated.

Sodium dodecyl benzene sulphonate mediated tautomerism of Eriochrome Black-T: Effect of charge transfer interaction

Interaction between anionic surfactant, sodium dodecyl benzene sulphonate, (SDBS) and an anionic dye Eriochrome Black-T, (EBT) has been investigated by visible spectroscopy, conductometry, dynamic light scattering and zeta potential measurements. Spectral changes of EBT observed on addition of SDBS indicate formation of quinone-hydrazone tautomer at pH 7.0, whereas in absence of SDBS this change appears at pH ∼ 9.45. However, at pH 7.0 this change in tautomerism is not observed in presence of sodium dodecyl sulphate (SDS). Experimental results indicate presence of charge transfer interaction between less stable quinone-hydrazone tautomer of EBT and SDBS molecules, which is confirmed using Benesi–Hildebrand and Scott equations.

Ground-state charge-transfer complex formation in hybrid poly(3-hexyl thiophene):titanium dioxide solar cells

The existence of a ground-state charge-transfer (CT) complex in a conjugated polymer:metal oxide nanoparticle bulk heterojunction photovoltaic cell is demonstrated by Fourier-transform photocurrent spectroscopy (FTPS). The CT complex between poly(3-hexylthiophene) (P3HT) and titanium dioxide (TiO2) is characterized by a weak additional photocurrent band (onset 1eV) in the FTPS spectra, situated below the conjugated polymer bandgap of 2eV. The presence of CT interaction between P3HT and TiO2 in relation to frontier orbital alignment is discussed, as well as the contribution of a sub-bandgap interfacial CT state to the electron transfer process in P3HT:TiO2 solar cells.

Dynamics of the Singlet Excited States of Diarylethenes in the Presence of Charge-Transfer Interactions. A Picosecond Laser Flash Photolysis Study

Charge-transfer interactions of singlet excited trans isomers of n-styrylnaphthalene (n-StN, with n = 1 and 2), 9-styrylanthracene (9-StAn), and n-styrylphenanthrene (n-StPh, with n = 1, 2, and 9) with electron donors (N,N-diethylaniline, DEA, and 4-bromo-N,N-dimethylaniline, BrDMA) and acceptors (p-dicyanobenzene, DCNB) were studied in polar and nonpolar solvent at room temperature by absorption picosecond laser flash photolysis. The transient absorption formed within the laser pulse, already attributed to S1 → Sn and S2 → Sn transitions, were replaced, in the presence of amine quenchers, by the absorption of the exciplex (nonpolar solvent) or of contact radical ion pairs (CRIP, polar solvent). The time evolution of these transients showed the formation of the solvent-separated radical ion pair (SSRIP) and then of the longer-lived absorption of triplet state and/or radical anions. In the presence of DCNB in polar solvent the evolution of the first excited singlet showed the formation of CRIP, SSRIP, and ...

Molecular weight and stability of the charge transfer complex of poly(2-vinylpyridine) and 1,4-benzoquinone

The interaction between monodisperse poly(2-vinylpyridine) ( M ̄ w -M n = 1.1–1.5 ) and 1,4-benzoquinone was examined in aqueous alcohols. The presence of charge transfer interactions was examined spectrophotometrically by Benesi-Hildebrand plots. It was found that a negative molecular weight effect does exist whereby the level of interaction between poly(2-vinylpyridine) and benzoquinone decreases with increasing molecular weight. However, considerable time is required for the interaction to achieve equilibrium, with the kinetics of ‘complexation’ varying with the molecular weight of the polymer. An extensive spectroscopic investigation of the phenomenon confirms, however, that benzoquinone reacts over time with alcohols to form primarily 1,4-hydroquinone. Our results show that the molecular complex formed in these systems is probably due to the well documented quinhydrone complex between 1,4-hydroquinone and 1,4-benzoquinone.