T-shaped Molecules Research Articles

Optical anisotropy of retarder film made from mixtures of rodlike and T-shaped reactive molecules: dependence on the chemical structure of T-shaped molecules

Five kinds of T-shaped reactive molecules were newly synthesized for optical retarder films. The retarder films were fabricated using the mixtures of rodlike reactive mesogen (RM) and the T-shaped molecules. The effect of the chemical structure of the T-shaped molecules on the optical anisotropy of the retarder films was investigated. The retarder films with the T-shaped molecules resulted in a greater magnitude of an in-plane retardation. Among the five kinds of the T-shaped molecules, the molecule with five benzene rings along the longitudinal direction and two benzene rings along the lateral molecular direction showed the widest liquid crystalline phase and the largest optical retardation. In addition, the NZ coefficients of the films were greater than 1 implying that the films were negative biaxial.

Theoretical investigation of nonlinear optical behavior for rod and T-Shaped phenothiazine based D-π-A organic compounds and their derivatives

The exploration of novel materials with excellent nonlinear optical (NLO) features is an area of frontline investigation for scientific community from technological point of view. This study reports the novel phenothiazine-based rod-shaped and T-shaped NLO molecules which are quantum chemically designed from synthesized compounds: rod-shaped (CFA and CBA) and T-shaped (CTA, CCA and CPA). Structural tailoring was performed on D-π-π-A centered CPA chromophore and the effect of various π-spacers, as well as solvents on NLO response properties is investigated. Density functional theory (DFT) along with time dependent DFT (TDDFT) calculations have been executed at B3LYP/6-311G(d,p) functional to examine entire analysis. Results showed a smaller energy gap in structurally modified compounds as compared to reference CPA. Global reactivity parameters analysis revealed smaller hardness and larger softness values in T-shaped compounds. UV–Vis analysis of investigated molecules displayed a red shift in absorption maximum value as compared to CPA. Natural bond orbital (NBO) and frontier molecular orbital (FMO) analysis revealed the stability and intra-molecular electron transferring (ICT) process in investigated molecules. ICT showed the effective charge shift from donor to acceptor via π-spacers. Overall, promising NLO response exists in gas phase and different solvents (acetonitrile, ethyl alcohol and water). Interestingly, proposed molecule CPP presented a maximum value of linear polarizability < α > as 1518.23 a.u and first hyperpolarizability (βtot) as 755322.39 a.u in acetonitrile solvent. In short, entitled chromophores exhibited excellent NLO properties due to their lower charge transport resistance. This NLO study may open a new topic for researchers to discover novel NLO for hi-tech submissions of modern era.

Concise Approach to T-Shaped NBN-Phenalene Cored Luminogens as Intensive Blue Light Emitters.

Small organic molecules with finely tunable physical properties are highly desired for the fabrication of low-cost and high-performance organic electronic devices. In this work, the syntheses of a series of T-shaped NBN-embedded dibenzophenalene derivatives through the formation of a key brominated intermediate in a stoichiometrically controlled reaction are presented. The geometric and electronic structures of these T-shaped molecules can be simply tailored by attaching substituents along the direction perpendicular to the molecular main backbones, resulting in desirable physical properties, such as high thermal stability with a decomposition temperature of more than 350 °C, and intensive blue luminescence with a quantum yield up to 0.62. Organic light-emitting diode devices fabricated with such molecules as the emitting layer release pure blue light with CIE (0.16, 0.12).

2,3-di(2-furyl) quinoxaline bearing 3 -ethyl rhodanine and 1,3 indandione based heteroaromatic conjugated T-shaped push -pull chromophores: Design, synthesis, photophysical and non-linear optical investigations

The design, synthesis, computational, spectroscopic, and, the second and third order non-linear optical studies of a two new π-deficient cross-conjugated T-shaped push-pull molecules (QFR and QFI) consisting of 3-ethyl rhodanine and 1,3 indandione substituted with heterocyclic quinoxaline ring were synthesized by Knoevenagel condensation reaction of the precursor dialdehydes with active dye molecules were described in detail. In the as synthesized molecule, the electron donating thiophene moiety acts as an efficient π-bridge on either side to the quinoxaline core that permits good viability in fine-tuning the optical absorption spectrum with good solubility. The computational studies of these molecules show efficient intra molecular charge transfer (ICT) processes analyzed through their molecular orbital characteristics, excitation energy, absorption maxima, oscillator strength and Mulliken population analysis. The comparison study between the structures of these push-pull molecules were done by their photophysical characteristics including CIE coordinates; thermal characteristics, XRD studies and electrochemical analysis. The time-resolved fluorescence spectra with nanosecond time profile were measured to detect the delayed fluorescent performance of the push-pull molecules QFR and QFI. Hyper-Rayleigh scattering (HRS) in chloroform solution of varying concentrations, using a standard wavelength at 1064 nm was used to assess their first order hyperpolarizability. Optical non-linear property was again proved by open-aperture Z-scan technique investigated at 532 nm and the observed optical limiting behavior was originated from the reverse saturable absorption (RSA) process. The second and third order NLO studies reveals that 3-ethyl rhodanine substituted QFR molecule (β value from HRS, 84.64 × 10−30 esu and βeff from Z scan, 10 × 10−10 m/W) shows high non-linear optical properties and thermal stability compared with 1,3 indandione substituted QFI (β value from HRS, 48.00 × 10−30 esu and βeff value from Z scan, 2 × 10−10m/W).

Heteroatom-mediated performance of dye-sensitized solar cells based on T-shaped molecules

Two novel “sister” organic dyes featuring a T-shape molecular pattern based on phenothiazine/phenoxazine and triphenylamine framework as electron donor core and cyanoacrylic acid as acceptor and anchoring group were designed, synthesized and thoroughly characterized. Both dyes were functionalized at the nitrogen atom of phenoxazine/phenothiazine with the triphenylamine unit containing two hexyloxy substituents to obtain a T-shape configuration. The photo-optical and electrochemical data corroborated with time-dependent density functional theory computations and photovoltaic features were discussed in correlation with the structural architecture of each dye. Their performances in dye-sensitized solar cells (DSSCs) were comparatively surveyed with a special concern on the influence of the heteroatom variation on the most important DSSCs characteristics. In spite of its more favorable optical performance, the cells realized with phenoxazine-based dye are less efficient than those fabricated with phenothiazine ones. The cause is the stronger electron interception by the electrolyte in the case of phenoxazine dye which consistently degrades the open-circuit voltage, corroborated with a better regeneration of the phenothiazine by the iodine/iodide redox couple. In fact, to the best of our knowledge, this is one of the first studies which highlights how a single heteroatom in a T-shape dye structure can affect the dye interaction with the electrolyte and its regeneration, consequently the photovoltaic performances and brings out new opportunities for developing novel dyes for efficient DSSCs.

Capture and Translocation Characteristics of Short Branched DNA Labels in Solid-State Nanopores

The challenge when employing solid-state nanopores as single-molecule sensors in a given assay is the specificity of the ionic current signal during the translocation of target molecules. Here we present the capture and translocation characteristics of short structurally defined DNA molecules that could serve as effective surrogate labels in biosensing applications. We produced T-shaped or Y-shaped DNA molecules with a 50 bp double-stranded DNA (dsDNA) backbone and a 25 bp dsDNA branch in the middle, as improved labels over short linear DNA fragments. We show that molecular topologies can be distinguished from linear DNA by analyzing ionic current blockades produced as these DNA labels translocate through nanopores fabricated by controlled breakdown on 10-nm-thick SiN membranes and ranging in diameter from 4 to 10 nm. Event signatures are shown to be a direct result of the structure of the label and lead to an increased signal-to-noise ratio over that of short linear dsDNA, in addition to well resolved dwell times for the pore size in this range. These results show that structurally defined branched DNA molecules can be robustly detected for a broad range of pore size, and thus represent promising candidates as surrogate labels in a variety of nanopore-based molecular or immunoassay schemes.

Skeletal cubic, lamellar, and ribbon phases of bundled thermotropic bolapolyphiles.

A series of T-shaped polyphilic molecules composed of a rigid linear biphenyl core with a polar glycerol group at each end and one swallow-tail semiperfluorinated lateral chain were synthesized and their thermotropic liquid crystalline (LC) phases were investigated by X-ray diffraction, calorimetry, and microscopy. The compounds have a long alkyl spacer between the aromatic core and the fluorinated C(n)F(2n+1) ends, where n = 4, 6, 8, and 10. Upon melting, all compounds start with lamellar LC phases, followed on heating by a rectangular columnar ribbon phase with c2mm symmetry. Unusually, a ribbon is a flat bundle of molecular cores highly aligned parallel to the ribbon axis. On further heating, for n = 8 and 10, this phase is succeeded by a bicontinuous cubic phase with Ia3d symmetry. This is a new variant of the "gyroid" phase, with axially oriented rod-like molecular cores forming the skeleton of the two infinite networks and junctions separated by exactly two molecular lengths. In this tricontinuous core-shell structure (aromatic-aliphatic-perfluoroalkyl), the polar glycerol domains of appreciable size, contained within the skeleton, can be considered as micellar.

Charge Transfer Emission of T-Shaped π-Conjugated Molecules: Impact of Quinoid Character on the Excited State Properties

We investigate the impact of quinoid character of a π-conjugation system on the emission properties of T-shaped cross-conjugated molecules. Three π-conjugated systems with different quinoid nature including benzothiophene, 2-phenylthiophene, and 2-phenylthieno[3,2-b]thiophene were connected orthogonally to a π-conjugated bis(phenylethynyl)arylene with an acid responsive N-methylbenzimidazole junction. The enhancement of quinoid character of a vertical π-system effectively suppressed the twisted intramolecular charge transfer (TICT) emission, leading to a more planar ICT state with enhanced emission intensity as well as a shortened Stokes shift.

3-(1,3-Diphenylpropan-2-yl)-4-methyl-6-phenylisoxazolo[3,4-d]pyridazin-7(6H)-one

In the title compound, C27H23N3O2, the geminal benzyl groups branching out from the methine adjacent to the isoxazole group are both syn-oriented to the methyl group of the pyridazinone moiety, as reflected by C—C distances of 3.812 (2) and 4.369 (2) Å between the methyl carbon and the nearest ring carbon of each benzyl group. This kind of conformation is retained in CDCl3 solution, as evidenced by distinct phenyl-shielding effects on the 1H NMR signals of the methyl H atoms. The isoxazolo[3,4-d]pyridazin ring system is virtually planar (r.m.s. deviation from planarity = 0.031 Å), but the N-bonded phenyl group is inclined to the former by an ring–ring angle of 55.05 (3)°. In the crystal, the T-shaped mol­ecules are arranged in an inter­locked fashion, forming rod-like assemblies along [10-1]. The mol­ecules are held together by unremarkable weak C—H⋯N, C—H⋯O and C—H⋯π inter­actions (C—O,N,C > 3.4 A), while significant π–π-stacking inter­actions are absent.

Dissipative Particle Dynamics Simulation of the Phase Behavior of T-Shaped Ternary Amphiphiles Possessing Rodlike Mesogens

We employed dissipative particle dynamics simulations to explore the phase behavior of T-shaped ternary amphiphiles composed of rodlike cores connected by two incompatible end chains and side grafted segments. By fine-tuning the number of terminal and lateral beads, three phase diagrams for the model systems with different terminal chain lengths are constructed in terms of temperature and lateral chain length, which have some common features and mostly compare favorably with experimental studies with the exception a couple of new phases. It is worthwhile to highlight that the mixed cylindrical phase and the perforated layer phase, as the experimentally observed mesophases exclusive for facial amphiphilies, are found in simulations for the first time. Also, a novel gyroid structure is observed in series of T-shaped ternary amphiphiles for the first time. Furthermore, by evaluating the effective volume fraction of lateral chains, the phase sequence spanning from conventional smectic layer phase via perforated layer structures and polygonal cylindrical arrays to novel lamellar mesophase is established, which is not just qualitatively consistent with the related experimental findings but even the stability windows of some mesophases quantitatively correspond well to experimental results. The success of reproducing the in-plane ordering of rods in the lamellar phase as well as the generic phase diagram of such T-shaped ternary amphiphiles in great detail implies that our genetic model qualitatively captures many of the characteristics of the phase behavior of real T-shaped molecules and could serve as a satisfactory basis for further exploration of self-organization in other related soft matter systems.

T-Shaped Donor–Acceptor Molecules for Low-Loss Red-Emission Optical Waveguide

A series of T-shaped polycyclic molecules with high fluorescence were developed as optical waveguide materials. Their emissions covered almost the whole visible range from 450 to 800 nm. Compound 3-1 showed an optical loss coefficient about 0.29 dB/μm in red-emission waveguide. Our investigations demonstrated that these molecules held great potential for organic optical waveguide due to the high fluorescence quantum efficiency and large Stokes' shift.

Dielectric spectroscopy of T-shaped blue-phase-III liquid crystal

Dielectric relaxation spectra of a liquid crystalline (LC) material showing blue-phase-III (BPIII) for a considerably large temperature regime consisting of T-shaped molecules are investigated. A low frequency relaxation mode is observed in the isotropic phase (I) as well as in BPIII of the investigating material which is attributed to the short axis rotation of the T-shaped molecules. The outcome of the temperature and dc bias field variation of dielectric strength (Δε) and relaxation frequency (ν(c)) in the vicinity of the I-BPIII transition is also discussed. The temperature dependence of ν(c) in BPIII with a minor deviation from Arrhenius activities in the fluctuation-dominated nonlinear region (FDNLR) is found to follow the unusual thermal behavior of the activation energy (E(A)). The growth of pretransitional fluctuations is found to be nonlinear in the vicinity of the I-BPIII transition. A moderate growth of transition fluctuation commences from the value of the exponent α(eff)=0.38/°C, which is obtained by an exponential variation of ν(c) with respect to temperature in BPIII. Observed dynamic phenomenon in the vicinity of the I-BPIII transition regions is explained on the basis of the Landau-de Gennes and Maier-Saupe Theories.

Prediction of quantum interference in molecular junctions using a parabolic diagram: Understanding the origin of Fano and anti- resonances

Recently the interest in quantum interference (QI) phenomena in molecular devices (molecular junctions) has been growing due to the unique features observed in the transmission spectra. In order to design single molecular devices exploiting QI effects as desired, it is necessary to provide simple rules for predicting the appearance of QI effects such as anti-resonances or Fano line shapes and for controlling them. In this study, we derive a transmission function of a generic molecular junction with a side group (T-shaped molecular junction) using a minimal toy model. We developed a simple method to predict the appearance of quantum interference, Fano resonances or anti- resonances, and its position in the conductance spectrum by introducing a simple graphical representation (parabolic model). Using it we can easily visualize the relation between the key electronic parameters and the positions of normal resonant peaks and anti-resonant peaks induced by quantum interference in the conductance spectrum. We also demonstrate Fano and anti-resonance in T-shaped molecular junctions using a simple tight-binding model. This parabolic model enables one to infer on-site energies of T-shaped molecules and the coupling between side group and main conduction channel from transmission spectra.

The Origin of the Emission Properties of π-Conjugated Molecules that have an Acid-responsive Benzimidazole Unit

The photophysical properties, especially the emission properties, of π-conjugated molecules with an acid-responsive N-methylbenzimidazole unit have been characterized and compared between T-shaped cross-conjugated and linear conjugated molecules. X-ray crystal structures and optimized structures based on DFT calculations suggest a planar conformation of the 2-thienyl-N-benzimidazole structure even after protonation where intramolecular S–N and NH–S interactions, respectively, are responsible for the stabilization of planar structures. Despite the planarity in the ground state, the T-shaped cross-conjugated molecules exhibit the twisted intramolecular charge-transfer (TICT) emission in response to protonation, whereas the corresponding linear conjugated molecule without a horizontal π-system does not have a charge-transfer state. The difference in the separation of frontier molecular orbitals of the HOMO and LUMO and the energy barrier of the rotation about the thienyl ring predicted by the DFT calculations accounts for the difference in the emission decay process between the linear and cross-conjugated molecules with a protonated benzimidazole unit. An orthogonally allocated π-conjugated system appears to be essential for the emergence of TICT characteristics upon protonation in terms of the separation of molecular orbitals of the HOMOs and LUMOs, as well as the ease of rotation.

Stabilization of blue phases by hydrogen-bonded bent-shaped and T-shaped molecules featuring a branched terminal group

The stabilization of liquid crystalline blue phases (BPs) from novel hydrogen-bonded (H-bonded) bent-shaped and T-shaped assemblies (HBAs) has been described for the first time in this study. Different kinds of H-bonded bent-shaped and T-shaped molecules were assembled, and then used to broaden the BP temperature range of liquid crystal (LC) samples. The results demonstrate that the temperature range of BPs is significantly influenced by HBA dopants, in which the widest BP temperature range was 15.1 °C. Moreover, the lower temperature of BPs is very close to room temperature, which is of benefit to the application of BPs in LC displays. Additionally, according to the experimental analysis and molecular simulations, the physical mechanism of the BP stabilization by bent-shaped and T-shaped molecules is mainly related to the molecular geometry and is not dependent on the LC phase. This study has developed a new and facile strategy to widen the BP temperature range from the aspect of the molecular design.

A T-Shaped Amphiphilic Molecule Forms Closed Vesicles in Water and Bicelles in Mixtures with a Membrane Lipid

The T-shaped amphiphilic molecule A6/6 forms a columnar hexagonal liquid-crystalline phase between the crystalline and the isotropic liquid when studied in bulk (Chen et al., 2005). Because of the hydrophilic and flexible oligo(oxyethylene) side chain terminated by a 1-acylamino-1-deoxy-d-sorbitol moiety attached to a rigid terphenyl core with terminal hexyloxy alkyl chains, it was expected that also formation of lyotropic phases could be possible. We therefore studied the behavior of A6/6 in water and also in mixtures with bilayer-forming phospholipids, such as dipalmitoyl-phosphatidylcholine (DPPC), using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), cryo-transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), and solid-state nuclear magnetic resonance (ssNMR). DSC showed for the pure A6/6 suspended in water a phase transition at ca. 23 °C. TEM and cryo-TEM showed vesicular as well as layered structures for pure A6/6 in water below and above this phase transition. By atomic force microscopy (AFM), the thickness of the layer was found to be 5-6 nm. This leads to a model for a bilayer formed by A6/6 with the laterally attached polar side chains shielding the hydrophobic layer built up by the terphenyl core with the terminal alkyl chains of the molecules. For DPPC:A6/6 mixtures (10:1), the DSC curves indicated a stabilization of the lamellar gel phase of DPPC. Negative staining TEM and cryo-TEM images showed planar bilayers with hexagonal morphology and diameters between 50 and 200 nm. The hydrodynamic radius of these aggregates in water, investigated by dynamic light scattering (DLS) as a function of time and temperature, did not change indicating a very stable aggregate structure. The findings lead to the proposition of a new bicellar structure formed by A6/6 with DPPC. In this model, the bilayer edges are covered by the T-shaped amphiphilic molecules preventing very effectively the aggregation to larger structures.

Polydentate-ligand-supported self-assembly of heterometallic T-shaped Co4Dy cluster showing slow magnetic relaxation

A novel mixed-valent heterometallic pentanuclear CoIII3CoIIDyIII cluster has been rationally assembled taking advantage of a bifunctional ligand with o-vanillin and tripodal tris(hydroxymethyl)aminomethane units. This unique heterometallic cluster represents a rare example of T-shaped molecules exhibiting slow magnetic relaxation.

Complex tiling patterns in liquid crystals

In this account recent progress in enhancing the complexity of liquid crystal self-assembly is highlighted. The discussed superstructures are formed mainly by polyphilic T-shaped and X-shaped molecules composed of a rod-like core, tethered with glycerol units at both ends and flexible non-polar chain(s) in lateral position, but also related inverted molecular structures are considered. A series of honeycomb phases composed of polygonal cylinders ranging from triangular to hexagonal, followed by giant cylinder honeycombs is observed for ternary T-shaped polyphiles on increasing the size of the lateral chain(s). Increasing the chain size further leads to new modes of lamellar organization followed by three-dimensional and two-dimensional structures incorporating branched and non-branched axial rod-bundles. Grafting incompatible chains to opposite sides of the rod-like core leads to quaternary X-shaped polyphiles. These form liquid crystalline honeycombs where different cells are filled with different material. Projected on an Euclidian plane, all honeycomb phases can be described either by uniformly coloured Archimedean and Laves tiling patterns (T-shaped polyphiles) or as multi-colour tiling patterns (X-shaped polyphiles). It is shown that geometric frustration, combined with the tendency to segregate incompatible chains into different compartments and the need to find a periodic tiling pattern, leads to a significant increase in the complexity of soft self-assembly. Mixing of different chains greatly enhances the number of possible 'colours' and in this way, periodic structures comprising up to seven distinct compartments can be generated. Relations to biological self-assembly are discussed shortly.

Preparation and Acid‐Responsive Photophysical Properties of T‐Shaped π‐Conjugated Molecules Containing a Benzimidazole Junction

T-shaped π-conjugated molecules with an N-methyl-benzimidazole junction have been synthesized and their acid-responsive photophysical properties owing to the change in the π-conjugation system are discussed. T-shaped π-conjugated molecules consist of two orthogonal π-conjugated systems including a phenyl thiophene extended from the 2-position and alkyl phenylenes connected through various π-spacers from the 4,7-positions of the N-methyl-benzimidazole junction. The π-spacers, such as thiophene, ethyne, and ethane, have an effect on the acid response of photophysical properties in terms of changes in conformation, excited-state energy and charge-transfer (CT) characteristics. In particular, the π-conjugated molecule with ethynyl spacers exhibited a marked redshift in the fluorescence spectrum with a large Stokes shift upon the addition of acid, whereas the other molecules showed substantial quenching. The redshift in emission was studied in detail by temperature-dependent fluorescence measurements, which indicated the transition to a CT state over the finite activation energy at the excited state. The change in the frontier molecular orbitals upon acid addition was further discussed by means of DFT calculations.

Self-Assembly of T-Shaped Polyphilic Molecules in Solvent Mixtures

Coarse-grained molecular simulations of a model of a T-shaped polyphilic molecule in the presence of solvents are presented. The target molecules are liquid crystal bolaamphiphiles with grafted lateral side chains. The main core of the molecule corresponds to a rigid biphenyl unit, decorated at both ends with polar associating sites. A lateral flexible chain, whose character is mostly antagonistic with respect to the rest of the molecule, imparts unique self-assembly behavior to the pure fluid. In the case herein, the pure T-shaped bolaamphiphile (TsB) forms two-dimensional honeycomb-like columnar structures, and a study is performed on the effects of solvents added to this structure. Three model solvents are considered, each corresponding to the three different parts of the original molecule. We consider the whole concentration range and a temperature at which the pure TsB fluid shows a columnar liquid crystal behavior. All three solvents show different progressions and equilibrium mesophases. The solvent compatible with the end groups swells the structure at low concentrations and at higher concentrations forces a phase split between an essentially pure solvent phase and a structured LC phase. The solvent affine with the core of the TsB does not swell the structure at low concentrations. At higher concentrations, this solvent induces a phase separation where the TsB-rich phase forms a unique liquid crystal membrane. The solvent compatible with the lateral chain will not form stable phase separations, but transforms the columnar structure into a loose, worm-like micellar network. The results reported are generic in nature and describe the phase space for the entire family of TsB's.