Truxene Core Research Articles

Rod–disc oligomeric liquid crystal based on 4-cyanobiphenyl and truxene core

ABSTRACTA facile synthesis of a novel covalently linked disc–rod mesogen is reported consisting of a truxene-based core attached to which are six 4-cyanobiphenyl units via flexible alkyl spacers. The compound formed a stable Langmuir monolayer at the air–water interface. The atomic force microscope study on the Langmuir–Blodgett film of the molecule reveals a tilted orientation at air–solid interfaces.

Synthesis of new dithieno[3,2-b:2′,3′-d]pyrrole (DTP) units for photovoltaic cells

Three new dithieno[3,2-b:2′,3′-d]pyrrole units (DTPA1–3) based on the truxene core have been designed and synthesized for a potential application in photovoltaic cells. One of these units (DTPA1) has been employed to construct a new organic dye (M47), exhibiting a higher solar-to-electrical energy conversion efficiency when compared to reference dyes (M48 and M49) under the same conditions. Absorption spectra, electrochemical cyclic voltammetry, theoretical calculations, current voltage curves and controlled intensity modulated photovoltage spectroscopy have been investigated. M47 sensitized solar cells employing a cobalt electrolyte afford a short circuit photocurrent of 12.1 mA cm−2, an open circuit voltage of 758 mV, and a fill factor of 0.56, corresponding to an overall power conversion efficiency of 5.1% under standard AM 1.5 sunlight. These results suggest that the truxene-substituted dithieno[3,2-b:2′,3′-d]pyrrole derivatives are promising candidates for photovoltaic cells.

A new thermal-stable truxene-based hole-transporting material for perovskite solar cells

Developing effective hole-transporting material is critical to achieve high efficiency CH3NH3PbI3 perovskite solar cells. A new thermal-stable truxene-based material, 2,7,12-tri(N,N-di(4-methoxyphenyl)amino)-5,5′,10,10′,15,15′-hexapropyltr-uxene, has been synthesized by a facile route. A reference compound, 1,3,5-tris(di-p-anisylamino)benzene, was prepared as well. Their optical, electronic properties, thermal stability and photovoltaic performances were investigated. This new truxene-based material exhibits a high decomposition temperature (432 °C), a high glass transition temperature (134 °C), and a suitable highest occupied molecular orbital level well-matched with the valence band of CH3NH3PbI3. The device based on this new material in conjunction with a carbon counter electrode achieves a power conversion efficiency of 3.18% under the illumination of 100 mW cm−2, which is better than that of the reference compound (0.93%). These results indicate truxene core is a promising building block for hole-transporting material.

Pyrene‐Capped Conjugated Amorphous Starbursts: Synthesis, Characterization, and Stable Lasing Properties in Ambient Atmosphere

A family of trigonal starburst conjugated molecules (TrFPy, TrFPy, and TrF2Py) composed of a truxene core and pyrene cappers with various bridge lengths is synthesized and characterized. The incorporation of pyrene cappers successfully depress the crystallization tendency, resulting in enhanced glassy temperature and improved morphological stability of the thin films. The high photoluminescence yield in neat films and excellent thermal stability render these pyrene‐capped starbursts promising lasing optical gain media. Low amplified spontaneous emission (ASE) thresholds (EthASE) of 180 nJ pulse‐1 and 101 nJ pulse–1 were recorded for TrFPy and TrF2Py, respectively. One dimensional distributed feedback (1D DFB) lasers demonstrated lasing threshold of 9.3 kW/cm2 and 7.3 kW/cm2 for TrFPy (at 457 nm) and TrF2Py lasers (at 451 nm), respectively. The ASE performance of TrFPy and TrF2Py in an ambient condition was recorded with various annealing temperature (from 80 to 250 °C, 10 min). Surprisingly, TrFPy exhibited excellent ASE stability in an ambient condition, which is still detectable even after annealing at 250 °C for 10 min. The results suggest the pyrene‐capped molecular design strategy is positive on improving the optical gain stability and meanwhile maintaining excellent lasing properties.

Synthesis and two-photon absorption properties of truxene-cored chromophores with functionalized pyrazine units fused as the end-groups

A new set of model chromophores derived from a truxene core fused with varied number and size of functionalized pyrazine units was designed and synthesized for the tentative exploration of possible connections between the molecular structure and their linear/nonlinear optical properties. The initial experimental results have indicated that these model compounds not only possess strong and widely dispersed two-photon absorption (2 PA) within the near-IR region but also show the ascending overall 2 PA when the molecular structure varies with increase in complexity and molecular weight, which implies that both the number of branches and the size of π-framework are important factors to the molecular 2 PA in this model chromophore system. On the other hand, the studied model chromophores also manifest very good photostability within their two-photon active spectral region even under a prolonged irradiation of IR laser pulses. In addition, a representative chromophore is selected to demonstrate optical power-limiting and power-stabilization performance against nanosecond laser pulses.

Dye-sensitized solar cells based on functionalized truxene structure

Abstract Three new metal-free organic dyes ( TX1 , TX2 and TX3 ) based on truxene core structure, with triphenylamine as the electron donor, thiophene as the π spacers, and cyanoacetic acid or rhodanine-3-acetic acid as the electron acceptor are designed and synthesized. Their UV–vis absorption spectra, electrochemical and photovoltaic properties were investigated. The cyanoacrylic acid is verified to be a better acceptor unit (meanwhile the anchoring group) compared to the rhodanine-3-acetic acid. And also, two anchoring groups in TX2 could provide stronger adsorption ability on the TiO 2 surface. In addition, the EIS results indicate a slower charge recombination processes for TX2 . As a result, dye TX2 bearing two cyanoacetic acid outperforms the other two dyes, exhibiting the photo-conversion efficiency of 2.64%, with J sc = 5.09 mA cm –2 , V oc = 729 mV, FF = 71.1.

Synthesis, characterization and nonlinear optical studies of novel blue-light emitting room temperature truxene discotic liquid crystals

A new series of discotic liquid crystals based on a truxene core has been synthesized to study the structure–property relationship in view of the self-assembling property and their linear and nonlinear optical properties.

Star shaped ferrocenyl truxenes: synthesis, structure and properties

This article reports the design and synthesis of star shaped, C3-symmetric ferrocenyl substituted truxenes by the Pd-catalyzed Sonogashira cross-coupling and cycloaddition reaction. The single photon absorption and electrochemical properties indicate significant electronic interaction between ferrocene and truxene core. The bathochromic shift in the absorption spectra of truxenes 4a-4c and 5a is a function of enhanced conjugation. The incorporation of tetracyanoethylene (TCNE) results in a strong charge transfer band in truxene 5a. The single crystal structure of truxene 4a is presented, which shows interesting supramolecular interactions.

Star-shaped chromophores based on a benzodithiophene fused truxene core for solution processed organic solar cells

By fusing three benzodithiophenes with a truxene, a new planar aromatic electron-rich core was synthesized, which was used for the construction of novel star-shaped chromophores with various terminal groups. The absorption maxima of the synthesized star-shaped chromophores in thin film are varied from 366 nm to 527 nm depending on the electron donating/accepting properties of the terminal groups. Bulk heterojunction (BHJ) photovoltaic devices were fabricated by using the star-shaped chromophores as donor materials and (6, 6)-phenyl C71-butyric acid methyl ester (PC71BM) as an acceptor material. The fabricated solar cells showed open circuit voltages (Voc) in the range of 0.86–1.07 V, which are related with the energy difference between HOMO energy levels of the chromophores and the LUMO energy level of PC71BM. BHJ photovoltaic devices based on one of these star-shaped chromophores exhibit a power conversion efficiency of 2.40% without extended optimization.

π-Conjugated Molecules Based on Truxene Cores and Pyrene Substitution: Synthesis and Properties

Two starburst molecules based on pyrene with truxene cores, PYT and PYET, have been designed and synthesised by Pd(0)-catalysed Suzuki coupling and Sonogashira coupling reactions, respectively. Due to the different conjugation length, the solution absorption and emission spectra of PYET in dilute THF were redshifted compared with those of PYT. The solid absorption and emission spectra of PYET were also redshifted. Their thermal decomposition temperatures ( Td) were over 400 °C, and the glass transition temperatures ( Tg) were 96 and 124 °C, respectively, which showed that both materials possess good thermal stability. Electrochemical analysis implied that the HOMOs of PYET and PYT were similar.

Location, Location, Location ‐ Strategic Positioning of 2,1,3‐Benzothiadiazole Units within Trigonal Quaterfluorene‐Truxene Star‐Shaped Structures

AbstractThe fused, bicyclic molecule, 2,1,3‐Benzothiadiazole (BT), has become a key ingredient in the design of new organic semiconductors for light emission and energy harvesting applications. Here, the synthesis is reported of a series of trigonal, star‐shaped compounds comprising a truxene core and three quater‐dialkylfluorene arms into each of which a BT unit is inserted sequentially at each possible position (T4BT‐A to T4BT‐E). Analysis of the resulting electronic properties shows that as a consequence of conjugative coupling to the core and the resulting symmetry there are three distinct locations for the BT unit and the influence that these locations have on light emission and other spectroscopic characteristics is discussed. The systematic variation in photophysical properties for the different structural isomers helps to clarify the influence of BT unit addition to 9,9‐dialkylfluorene chains. It also helps to establish a design template for the construction of donor‐acceptor conjugated materials with targeted properties. For T4BT‐E with a BT unit at the terminal position of each arm, the photoluminescence quantum efficiency is significantly reduced and no amplified spontaneous emission is observed under typical pumping conditions. Theoretical calculations assist in understanding the variation in behaviors among the T4BT‐X family of compounds, especially in relation to their photoluminescence decay times and the Raman scattering intensities of their dominant BT‐unit‐centred molecular vibrations.

Fusing three perylenebisimide branches and a truxene core into a star-shaped chromophore with strong two-photon excited fluorescence and high photostability

A novel star-shaped chromophore, Tr-PBI, was constructed by fusing three perylenebisimide branches and a truxene core. Tr-PBI exhibits high photostability and excellent two-photon properties: the maximum of δ(TPA) is 11,000 GM at 990 nm and fluorescence quantum efficiency Φ is 0.40 in THF.

Dynamics of fluorescence depolarisation in star-shaped oligofluorene-truxene molecules

Star-shaped molecules are of growing interest as organic optoelectronic materials. Here a detailed study of their photophysics using fluorescence depolarisation is reported. Fluorescence depolarisation dynamics are studied in branched oligofluorene-truxene molecules with a truxene core and well-defined three-fold symmetry, and are compared with linear fluorene oligomers. An initial anisotropy value of 0.4 is observed which shows a two-exponential decay with time constants of 500 fs and 3-8 ps in addition to a long-lived component. The femtosecond component is attributed to exciton localisation on one branch of the molecule and its amplitude reduces when the excitation is tuned to the low energy tail of the absorption spectrum. The picosecond component shows a weak dependence on the excitation wavelength and is similar to the calculated rate of the resonant energy transfer of the localised exciton between the branches. These assignments are supported by density-functional theory calculations which show a disorder-induced splitting of the two degenerate excited states. Exciton localisation is much slower than previously reported in other branched molecules which suggests that efficient light-harvesting systems can be designed using oligofluorenes and truxenes as building blocks.

Manipulating the nanostructure of organogels generated from molecules with a 3-dimensional truxene core

Two new truxene-based 3-dimensional (3-D) molecules self-assembled in cyclohexane to give organogels with vesicular and fibrillar nano-morphologies governed by the substitution pattern of the peripheral alkyl amido side-chains grafted onto the rigid 3-D core.

Bowl-shape electron donors with absorptions in the visible range of the solar spectrum and their supramolecular assemblies with C60

We describe the synthesis, electronic, optical and photophysical properties of a family of three electron-donor bowl-shaped organic molecules that absorb light in the whole range of the visible spectrum (up to 800 nm in one case), and associate C60 in solution with binding constants in the range of 104–102 M−1 as measured from both UV-vis and fluorescence titrations in several solvents. These molecules are π-extended derivatives of tetrathiafulvalene, based on a truxene core to which two or three units of dithiole are covalently attached. The inclusion of the bulky dithiole groups is responsible for their bowl-shape geometry, which allows them to associate with C60, and their electron-donor character. The symmetric derivative 1, with three dithiole units, absorbs light in the 370–520 nm range. Exchanging one of the dithiole groups by an electron-withdrawing group, ketone (2) and dicyanomethylene (3), results in an intramolecular push–pull effect that extends the absorption to nearly 700 nm in the case of 2, and up to 800 nm in the case of 3. Transient absorption measurements, supported by spectroelectrochemical and radiolytical experiments, reveal that upon photoexcitation of the 1∙C60 associate the fully charge-separated state 1•+∙C60•− is generated, with lifetimes of hundreds of picoseconds. Molecular-level understanding of the electronic and supramolecular properties of 1–3 is provided by density functional theory calculations.

Water-soluble anionic fluorophores from truxene

Two new water-soluble fluorophores are synthesized from truxene and ester-substituted aryl acetylenes. The truxene core is decorated by 2-(2′-methoxy)ethoxyethyl groups to enhance the hydrophilicity of these fluorophores as well as to prevent the aggregation by π-stacking in aqueous media. The conjugated structures are assembled by iodination of the truxene core and subsequent Sonogashira coupling with aryl acetylenes. Upon the hydrolysis of the ester groups, water-soluble fluorophores are obtained in good to excellent yield (30–71% for 3 steps). A photophysical investigation reveals that these compounds exhibit strong fluorescence signals (quantum yield 46–63%) with maximum emission wavelength around 390–400 nm in aqueous phosphate buffer. Preliminary screening on sensing application shows that their fluorescent signals can be selectively quenched by porphyrin-containing metalloproteins.

Facile Synthesis of 5,10,15-Hexaaryl Truxenes: Structure and Properties

A new synthesis of 5,10,15-hexaaryltruxene derivatives has been developed. Experimental observations and theoretical calculations confirmed that the presence of aryl substituents on the sp(3)-hybridized bridge carbon atoms had an effect on the photophysical properties of the truxene core. Interestingly, the cage compound 11 possessing a distorted truxene core was verified by X-ray diffraction analysis; the influence of the peripheral aryl substituents on the photophysical properties of the truxene core was diminished because of its molecular rigidity.

Energy Transfer Dynamics in Multichromophoric Arrays Engineered from Phosphorescent PtII/RuII/OsII Centers Linked to a Central Truxene Platform

A rigid star-shaped tetrachromophoric trimetallic complex engineered from a 5,5',10,10',15,15'-hexabutyltruxene platform functionalized in the 2,7,12 positions with three different metal centers, namely, a terpyridine-Pt(II) ethynylene unit and Ru(II) and Os(II) bipyridine centers, was synthesized in a controlled fashion and characterized by (1)H NMR and mass spectrometry. The protocol was devised in such a way that key mono and dinuclear model complexes and two reference truxene ligands could also be prepared. Room temperature (RT) optical absorption and RT and 77 K luminescence studies were performed on the truxene ligands, the trimetallic species, the various mono- and binuclear complexes and precursors lacking the truxene fragment; RT nanosecond transient absorption measurements were also carried out in particular cases. The electronic properties of the Ru and Os subunits in the arrays were found to be unaffected by the presence of the truxene core whereas direct linking of the Pt subunit to the truxene via the σ-alkyne bond markedly influences the spectroscopic behavior of the Pt center. Remarkably the truxene phosphorescence was clearly established in the two ligands (lifetime of 4.3 s for the mono ethynyl-bipy substituted truxene and 17.5 ms for the bis ethynyl-bipy substituted truxene) and also detected in the Pt-containing complexes PtL' (model Pt-truxene) and Pt-Os (Pt-truxene-Os dyad) at low temperature. This is attributed to the closeness in energy of the Pt (3)CT level and the truxene triplet at low temperature and to the spin-orbit coupling induced by the Pt heavy atom. Transient absorbance measurements evidenced the population of the Pt-based triplet in the Pt-truxene mononuclear complex PtL' at room-temperature. For the trimetallic complex, where the various centers exhibit an energy gradient for the local excited levels, and following an approach based on the use of selected excitation of the components, an initial energy transfer was found to occur from the central truxene unit toward the peripheral Pt, Ru, and Os metal-based centers. Subsequent Pt-based and Ru-based excited state depletion contributes to the final sensitization of the low-lying Os triplet excited state; the excited state dynamics for these multicascade processes are examined in detail.

2,3,7,8,12,13‐Hexaaryltruxenes: An ortho‐Substituted Multiarm Design and Microwave‐Accelerated Synthesis toward Starburst Macromolecular Materials with Well‐Defined π Delocalization

We present herein a novel design and the efficient synthesis towards a "homogeneous" starburst fluorene system based on the novel 2,3,7,8,12,13-hexaaryltruxene scaffold. Controlled microwave heating provides a facile and powerful approach for each step in the synthesis of these bulky materials with large steric hindrance, suggesting an avenue to access structurally well-defined complex organic semiconductors (OSCs) rapidly and conveniently with high yield and purity. The resulting materials exhibited good thermal stability and an excellent glassy structure as revealed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) as well as wide-angle X-ray diffraction (WAXD) studies. Moreover, compared with their corresponding three-arm-substituted counterparts T1-T4, the introduction of the ortho substituents around the truxene core in Tr1-Tr4 results in significant blueshifts (of 7-24 nm) of the absorption maxima lambda(max) and higher energy optical gaps (E(g)). Comparative studies with corresponding linear, rod-shaped oligofluorene counterparts (OFX) have revealed that the longest para-conjugated segment in the TrX (X=1-4) structures plays the dominant role in determining their electronic properties. UV/Vis data and cyclic voltammetry (CV) investigations have indicated that there is little electronic interaction between the arms, even for the shortest armed oligomer Tr1. A clear linear relationship of both 1/lambda(max) and E(g) with the inverse of (n+1) for these branched systems was found. Our findings highlight a novel molecular design comprising an ortho-substituted, multiarmed architecture that would allow the introduction of isotropic physical and/or mechanical properties, while at the same time maintaining most of the important electronic properties of the rod-shaped constituents of a fully conjugated system.

A Pre-organised Truxene Platform for Phosphorescent [Ru(bpy)2] and [Os(bpy)2] Metal Centres: A Clear-Cut Switch from Förster- to Dexter-Type Energy-Transfer Mechanism

We report on the synthesis, optical properties and energy-transfer features of a series of transition-metal-containing complexes and dyads, based on a pre-organised truxene scaffold. In this series, the [Ru(bpy)(3)](2+) and [Os(bpy)(3)](2+) photoactive terminals are coupled to the bridging aromatic truxene core through rigid ethynyl linkers. The photoinduced energy-transfer processes taking place from the Ru- to the Os-based levels, and from the truxene bridging ligand to the terminal-metal chromophores are studied and the pathways and mechanisms are discussed. The photoinduced energy-transfer process observed in the dyad proceeds rapidly through: i) an efficient (1)L-->(1)Os direct energy transfer followed by intersystem crossing to (3)Os, and ii) a fast (1)L-->(1)Ru energy-transfer step and subsequent intersystem crossing to (3)Ru followed by a (3)Ru-->(3)Os energy-transfer process. The first (1)L-->(1)Os and (1)L-->(1)Ru steps are controlled by a dipole-dipole interaction (Förster mechanism), whereas the subsequent (3)Ru-->(3)Os step proceeds by means of a long-range (approximately 24 A) through-bond mediated Dexter mechanism, facilitated by the conjugation along the bpy-truxene-bpy molecular axis.