A Redox-ActiveC3-Symmetric Triindole-Based Triazacyclophane

Simple Functionalization of a Donor Monomer to Enhance Charge Transfer in Porous Polymer Networks for Photocatalytic Hydrogen Evolution

Porous polymer networks (PPNs) are promising candidates as photocatalysts for hydrogen production. Constructing a donor-acceptor structure is known to be an effective approach for improving photocatalytic activity. However, the process of how a functional group of a monomer can ensure photoexcited charges transfer and improve the hydrogen evolution rate (HER) has not yet been studied on the molecular level. Herein, we design and synthesize two kinds of triazatruxene (TAT)-based PPNs: TATR-PPN with a hexyl (R) group and TAT-PPN without the hexyl group, to understand the relationship between the presence of the functional group and charge transfer. The hexyl group on the TAT unit was found to ensure the transfer of photoexcited electrons from a donor unit to an acceptor unit and endowed the TATR-PPN with stable hydrogen production.

Triple B←N Lewis Pair-Functionalized Triazatruxenes with Large Stokes Shifts

A novel class of multiple B←N Lewis pair-functionalized polycyclic aromatic hydrocarbons with different BR2 groups (R = Cl or Et) directly attached at positions 1, 6, and 11 of triazatruxene was synthesized. The triazatruxene backbone of 4 displays a bowl shape, and its molecular skeleton shows a highly twisted propeller-like structure with C3 symmetry. The introduction of B←N Lewis pairs not only results in a large decrease in the HOMO-LUMO gap but also lowers the LUMO to -3.00 eV. Both compounds show excellent stability with large Stokes shifts of ≤8234 cm-1 and solvatochromic emission in solvents of different polarities.

From truxenes to heterotruxenes: playing with heteroatoms and the symmetry of molecules

As a result of the modification of truxene, we can change the electronic structure or create multidimensional materials. Thus, the use of truxenes is very wide.

Functionalization at Nonperipheral Positions of Triazatruxene: Modular Construction of 1,6,11-Triarylated-Triazatruxenes for Potentially Organic Electronics and Optoelectronics

Functionalization from nonperipheral positions of triazatruxene is representing a challenge. Triarylation of the nonperipheral positions (1, 6, and 11) in triazatruxene scaffold has been achieved for the first time via two approaches. The transformations involve arylation/cyclotrimerization and cyclotrimerization/arylation sequences. POCl₃-mediated direct cyclotrimerization of oxindoles containing electron-deficient substituents on the aryl group at the C7-position resulted in the formation of 2-chloroindoles, whereas oxindoles containing electron-donating substituents gave the triazatruxenes. Furthermore, desired triazatruxenes were achieved through cyclotrimerization of 7-bromooxindole followed by coupling with arylboronic acids. NMR structural analysis exhibited that two of the suitably substituted oxindole and triazatuxene may have atropisomerism at room temperature. As a representative triazatruxene scaffold, the optoelectronic properties of 9a have also been studied via ultraviolet-visible (UV-vis) absorption spectra and fluorescence spectra of 9a thin films. Also, density functional theory calculation was realized to get knowledge about frontier molecular orbitals. In the light of the information obtained, an organic light-emitting diode (OLED) device utilizing 9a as an emissive layer was applied to obtain white emission. In brief, this study provides the first examples of the synthesis of triazatruxenes bearing aryl substituents at the nonperipheral positions as candidate compounds for organic electronics, optoelectronics, and material chemistry.

Synthesis, Structure and Supramolecular Properties of a Novel C3 Cryptand with Pyridine Units in the Bridges

The high-yield synthesis and the structural investigation of a new cryptand with C3 symmetry, exhibiting 2,4,6-triphenyl-1,3,5-triazine central units and pyridine-based bridges, are reported. The structure of the compound was investigated by single crystal X-ray diffractometry, NMR (nuclear magnetic resonance), HRMS (high resolution mass spectrometry) measurements, and theoretical calculations. The study of supramolecular behavior in solid state revealed the association of cryptand molecules by C-H---π and π---π contacts. Moreover, theoretical calculations indicated the high binding affinity of the cryptand for various organic molecules as guests.

Toward Soluble 5,10-Diheterotruxenes: Synthesis and Reactivity of 5,10-Dioxatruxenes, 5,10-Dithiatruxenes, and 5,10-Diazatruxenes

The following work presents three general approaches allowing, for the first time, the synthesis of 5,10-diheterotruxene derivatives containing two identical heteroatoms, namely, oxygen OOC, nitrogen NNC, or sulfur SSC. Two of described pathways involve the photocyclization of the corresponding triene 2 as a key step leading to a heptacyclic aromatic system. The third approach is based on the acidic condensation between ninhydrin 14 and benzo[b]heteroole 15. Typical functionalizations of the 5,10-diheterotruxene core have also been presented. In addition, the article discusses the advantages and limitations of the three suggested paths for receiving specific 5,10-diheterotruxene derivatives because the universal method suitable for obtaining molecules with any type of heteroatoms is not known so far.

Designing triazatruxene-based donor materials with promising photovoltaic parameters for organic solar cells

To address the increasing demand of efficient photovoltaic compounds for modern hi-tech applications, efforts have been made herein to design and explore triazatruxene-based novel donor materials with greater efficiencies. Five new molecules, namely M1-M5, were designed by structural modification of acceptor moiety (rhodanine-3-acetic acid) of well known experimentally synthesized JY05 dye (reference R), and their optoelectronic properties are evaluated to be used as donor molecules in organic solar cells. In these molecules M1-M5, triazatruxene acts as a donor unit and benzene spaced different end-capped moieties including 2-(4-(dicyanomethylene)-2-thioxothiazolidin-3-yl)acetic acid (A1), (E)-2-(4-(1-cyano-2-methoxy-2-oxoethylidene)-2-thioxothiazolidin-3-yl)acetic acid (A2), (Z)-2-(3'-ethyl-4'-oxo-2,2'-dithioxo-3',4'-dihydro-2'H,5H-[4,5'-bithiazolylidene]-3(2H)-yl)acetic acid (A3), (Z)-2-(4'-(dicyano-methylene)-3'-ethyl-2,2'-dithioxo-3',4'-dihydro-2'H,5H-[4,5'-bithiazol-ylidene]-3(2H)-yl)acetic acid (A4) and 2-((4Z,4'E)-4'-(1-cyano-2-methoxy-2-oxoethylidene)-3'-ethyl-2,2'-dithioxo-3',4'-dihydro-2'H,5H-[4,5'-bithiazolylidene]-3(2H)-yl)acetic acid (A5) respectively, as acceptor units. The electronic, photophysical and photovoltaic properties of the designed molecules M1-M5 have been compared with reference molecule R. All designed molecules exhibit reduced energy gap in the region of 1.464-2.008 eV as compared to reference molecule (2.509 eV). Frontier molecular orbital (FMO) surfaces confirm the transfer of charge from donor to acceptor units. All designed molecules M1-M5 exhibited an absorption spectrum in the visible region and they were broader as compared to that of reference R. Especially, M5 with highest λ max value 649.26 nm and lowest transition energy value 1.90 eV was accredited to the strong electron withdrawing end-capped acceptor moiety A5. The highest value of open circuit voltage (V oc) 1.02 eV with respect to HOMOdonor-LUMOBTP-4Cl was shown by M5 among all investigated molecules which was 0.15 V larger than reference molecule R. The designed molecule M5 is proven to be the best candidate for both electron and hole transport mobilities due to its smallest λ e (0.0212 eV) and λ h (0.0062 eV) values among all studied molecules.

Revisiting the intense NIR active bronzaphyrin, a 26-π aromatic expanded porphyrin: synthesis and structural analysis

Dithiabronzaphyrin, with intense absorption and fluorescence in the NIR region, was synthesized as its β-octaethyl analogue via a thiophene bridged terpyrrole. Solid state structural characterization obtained for the first time revealed inversion of the thiophene rings. Studies showed that there is no effect from protonation or temperature on the structural rigidity of the macrocycle. Crystal packing revealed four open dimeric trifluoroacetate [(CF3COO)2H]- moieties binding to the macrocycle in the protonated form via H bonding.

Branched truxene and triindole compounds and their solid-state luminescent enhancement

C3-symmetric truxene and triindole have been widely used to design the branched optoelectronic molecules. However, most of them exhibit high luminous efficiency in the solution and quenched luminescence in the solid state. Here, we respectively chose alkylated truxene and triindole as the central core, 2-methylphenyl as the peripheral functional groups to synthesize three branched compounds. Their photophysical properties have been explored combining with the theoretical calculation. The three compounds exhibit good solubility and high solid-state fluorescence quantum yields. The absorption and emission peaks of triindole compound exhibit apparent red-shift in comparison with those of truxene compounds, which indicates triindole more highly electron delocalization than truxene. The single-crystal structure shows that alkylation of the central core and branched steric bulkiness of these molecules effectively reduce the intermolecular π⋯π stacking and avoid the non-radiative transition of these molecules from excited state to ground state in the solid state.

Melanin-Inspired Organic Electronics: Electroluminescence in Asymmetric Triazatruxenes

The oxidative polymerization of 5,6-dihydroxyindoles and related hydroxyindoles at pH<3 is diverted from the usual eumelanin-forming pathway to produce mixtures of symmetric and asymmetric triazatruxenes (TATs), which could be separated and characterized for their opto-electronic properties with the aid of TD-DFT calculations. Data showed that the asymmetric isomers exhibit higher fluorescence quantum efficiencies, lower HOMO-LUMO gaps, better film homogeneity, and a more definite aggregation behavior than the symmetric counterparts, suggesting promising applications in organic electronics. The enhanced luminance exhibited by the OLED devices fabricated with blends of the synthesized TATs in poly-9-vinylcarbazole confirmed the potential of the asymmetric skeleton as new versatile platform for light-emitting materials.

Truxene: a promising scaffold for future materials

Truxene (10,15-dihydro-5H-diindeno[1,2-a;1′,2′-c]fluorene), which is a heptacyclic polyarene structure, has attracted a great deal of interest due to its exceptional solubility, high thermal stability and ease with which it may be modified.

Cryptands with 1,3,5-tris(1',3'-dioxan-2'-yl)-benzene units: synthesis and structural investigations

Various cryptands based on 1,3-dioxane decorated 1,3,5-trisubstituted-benzene building blocks, connected by different chains (exhibiting ester, ether, or triazol groups) to several units with C3 symmetry, are reported. The structure of the compounds was investigated by single crystal X-ray diffraction, NMR, and MS. The role of the 1,3-dioxane units was targeted to ensure the preorganization of the substrate for the macrocyclization reactions on one side, and for easier NMR assignment of the structure of the cryptands on the other side.

Ion exchange of protons by coinage metals to give gold and silver encapsulation within a pseudo-D2d distorted face-capped Pd14 cubic kernel: [(μ14-M)Pd22(CO)20(PEt3)8]+ (M = Au, Ag)

Heart of gold (or silver): The pseudo-D2d distorted MPd14 cubic kernel of [(μ14-M)Pd22(CO)20(PEt3)8](+) cations, with M = Au (1), Ag (2), has an encapsulated M atom (see picture; yellow) coordinated to eight cubic corner (black) and six face-capping Pd atoms (gray). Compounds 1 and 2 were obtained (28-60 % yields) from two-step/one-pot reactions of a Pd10 precursor with CF3CO2 H followed by coinage-metal ion exchange of protons.

Thiophene-functionalized octupolar triindoles: synthesis and photophysical properties

Two thiophene-functionalized octupolar triindole molecules were synthesized through Suzuki and Sonogashira cross-coupling reactions. Their photophysical and electrochemical properties were explored. The spectroscopic data demonstrate that triindole is an excellent rich electronic central donor for building octupolar optoelectronic molecules and possesses excellent luminescent properties. Thiophenylethynyl substituted triindole compound 3,8,13-tri(2-thiophenylethynyl)-5,10,15-tributyltriindole forms an intermolecular aggregation induced by π-π stacking from the rigid coplanar molecular scaffold. The redox curves and results of theoretical calculation imply that the two compounds have low ionization potential and low E(1/2 oxd), which may be originated from the high electronic density of both triindole and thiophene groups.

Solution-processable triindoles as hole selective materials in organic solar cells

We report the use of two solution-processable triindoles, triazatruxene (TAT), and N-trimethyltriindole (TMTI), as hole selective materials in organic solar cells. The unique optical and electronic properties of these molecules make them suitable as a hole extracting/electron blocking layer, i.e. transparency in the visible region due to a wide bandgap, high LUMO (lowest unoccupied molecular orbital) energy level, modest HOMO (highest occupied molecular orbital) level, and high hole carrier mobility. TAT is shown to have a LUMO at -1.68 eV, a HOMO at -5.03 eV, and a bandgap of 3.35 eV, whereas TMTI has a LUMO at -2.05 eV, a HOMO at -5.1 eV, and a bandgap of 3.05 eV, obtained from cyclic voltammetry measurements and absorption spectroscopy. Planar heterojunction photovoltaic devices, consisting of a solution processed transparent TAT (or TMTI) layer and a vapor-deposited C60 layer, exhibited efficiencies of up to 0.71 % (or 0.87 %). In these bilayer devices, the excitons are primarily generated in the C60 layer and undergo dissociation in the interfaces via hole transfer from the C60 layer to the TAT (or TMTI) layer. Additionally, spin-casting methanol solution of TAT on the top of P3HT:PCBM bulk heterojunction in an inverted device produced a hole selective interfacial layer between the photoactive layer and anode, leading to a 26% efficiency increase as compared to a control device without the TAT layer.

Synthesis and characterizations of star-shaped octupolar triazatruxenes-based two-photon absorption chromophores

A series of star-shaped octupolar triazatruxenes (TATs, 1-6) with intramolecular "push-pull" structure were synthesized and their photophysical properties have been systematically investigated. These chromophores showed obvious solvatochromic effect, i.e., significant bathochromic shift of the emission spectra and larger Stokes shifts were observed in more polar solvents mainly due to photoinduced intramolecular charge transfer (ICT). The two-photon absorption (2PA) cross-section values were determined by two-photon excited fluorescence (2PEF) measurements in toluene and THF. These chromophores exhibited large two-photon absorption cross-sections ranging from 280 to 1620 GM in the near-infrared (NIR) region. Compound 6 showed the largest 2PA action cross-section (σ(2)Φ) of 564 GM and could be a potential two-photon fluorescent (2PF) probe. In addition, compounds 1-6 all displayed good thermal stability and photostability.

Self-assembly of C3-symmetrical hexaaryltriindoles driven by solvophobic and CH-pi interactions

The synthesis and aggregation properties of a series of differently substituted star-shaped hexaaryltriindoles both in solution and in the solid state are being reported. While these molecules do not show any significant intermolecular aggregation in CDCl(3), it has been possible to induce aggregation by increasing the polarity of the solvent and therefore facilitating the occurrence of solvophobic forces. A study of the influence of the electronic character of peripheral substituents on the self-association behavior in solution has shown that increasing the electron-donor character of the substituents facilitates self-association while derivatives substituted with electron-acceptor substituents do not self-assemble. The electronic nature of the substituents also has an influence in the geometry of the stacking of these derivatives observed in the solid state. While unsubstituted hexaphenyl triindole self-assemble in a staggered face-to-face arrangement, attaching six cyano functional groups results in an offset stacking. The influence of the substituents in the strength and geometry of the stacking tendency contrasts with the trend expected for an aggregation induced solely by pi-pi interactions, but can be explained considering an important contribution of multiple cooperative CH-pi interactions.

Synthesis and preferred all-syn conformation of C3-symmetrical N-(hetero)arylmethyl triindoles

A new series of C(3)-symmetrical N-(hetero)arylmethyl triindoles has been synthesized in a straightforward procedure. The structure and conformation in the solid state have been determined for three derivatives (3, 4, and 6) by X-ray crystallographic analysis. In all three cases, the molecules adopt a tripodal conformation with all of the flexible arms directed towards the same side, thereby delimiting an inner cavity. Compound 6 crystallizes and forms C(3)-symmetric dimeric cagelike complexes. Guest molecules of chloroform and water are confined within the resulting cavities with stabilization by different intermolecular interactions; this highlights the potential of these compounds in the construction of supramolecular systems. A computational analysis has been performed to predict the most stable conformers. As a general trend, a preference for a conformation with all branches directed to the same side has been predicted. Comparison between theoretical and experimental results indicates that the computational level selected for the present study, B3LYP/6-31G*, is able to reproduce both the minimum energy conformations and the rotation barriers about the N--CH(2) bond.

Electroactive C3symmetric discotic liquid-crystalline triindoles

Discotic liquid crystals based on triindole, a novel redox active central core, have been synthesized and their mesomorphic behaviour investigated.