Novel truxene-based dipyrromethanes (DPMs): synthesis, spectroscopic characterization and photophysical properties.

For the first time, herein, we report the synthetic part of the truxene-centred mono-, di- and tri-substituted dipyromethanes (DPMs) in good yields (60-80%) along with their preliminary photophysical (absorption, emission and time resolved fluorescence lifetime) properties. The condensation reaction for assembling the required DPMs were catalyzed with trifluoroacetic acid (TFA) at 0 °C to room temperature (rt), and the stable dipyrromethanes were purified through silica-gel column chromatography. After successfully synthesizing these easy-to-make yet interesting molecules, they were fully characterized by means of the standard spectroscopic techniques (1H NMR, 13C NMR and HRMS). We are of the opinion that these truxene-based systems will be useful for diverse applications in future studies.

Synthesis, structure and photophysical properties of truxene and truxene-triindole compounds.

Multi-branched π-conjugated organic molecules, due to their fascinating structures and unique optical properties, exhibit potential applications in optoelectronics. Herein, series of 4-N,N-diphenylaminostyryl substituted multi-branched truxene compounds (namely TN1, TN2 and TN3) and a truxene-triindole compound (namely N3T3) were synthesized. These compounds are characterized by effective π-extension and remarkably enhanced two-photon absorption (TPA) compared to their less π-conjugated analogues. For truxene compounds, the more the number of the branch, the large the TPA efficiency, and the C3-symmetric three-branched TN3 exhibit the largest TPA. The aromatic triindole unit proves to be a better two-photon fluorophore compared with truxene. The results conclude that the influence of π-conjugation, molecular planarity and intramolecular charge-transfer (ICT) to TPA is far more pronounced than to linear optical properties.

Interfacial Layer Materials with a Truxene Core for Dopant-Free NiOx-Based Inverted Perovskite Solar Cells.

Nickel oxide (NiOx) is commonly used as a holetransporting material (HTM) in p-i-n perovskite solar cells. However, the weak chemical interaction between the NiOx and CH3NH3PbI3 (MAPbI3) interface results in poor crystallinity, ineffective hole extraction, and enhanced carrier recombination, which are the leading causes for the limited stability and power conversion efficiency (PCE). Herein, two HTMs, TRUX-D1 (N2,N7,N12-tris(9,9-dimethyl-9H-fluoren-2-yl)-5,5,10,10,15,15-hexaheptyl-N2,N7,N12-tris(4-methoxyphenyl)-10,15-dihydro-5H-diindeno[1,2-a:1',2'-c]fluorene-2,7,12-triamine) and TRUX-D2 (5,5,10,10,15,15-hexaheptyl-N2,N7,N12-tris(4-methoxyphenyl)-N2,N7,N12-tris(10-methyl-10H-phenothiazin-3-yl)-10,15-dihydro-5H-diindeno[1,2-a:1',2'-c]fluorene-2,7,12-triamine), are designed with a rigid planar C3 symmetry truxene core integrated with electron-donating amino groups at peripheral positions. The TRUX-D molecules are employed as effective interfacial layer (IFL) materials between the NiOx and MAPbI3 interface. The incorporation of truxene-based IFLs improves the quality of perovskite crystallinity, minimizes nonradiative recombination, and accelerates charge extraction which has been confirmed by various characterization techniques. As a result, the TRUX-D1 exhibits a maximum PCE of up to 20.8% with an impressive long-term stability. The unencapsulated device retains 98% of their initial performance following 210 days of aging in a glove box and 75.5% for the device after 80 days under ambient air condition with humidity over 40% at 25 °C.

Synthesis of a Benzotrisazulene via Trioxobenzotrisazulene.

Polycyclic aromatic hydrocarbons (PAHs) containing odd-membered rings (such as pentagons or heptagons) are fascinating synthetic targets. A special case is the introduction of five- and seven-membered rings in form of an azulene unit. Azulene itself is an aromatic compounds known for its deep blue color, which is a result of its internal dipole moment. When azulene is embedded into PAHs it can change the optoelectronic properties of the PAH significantly. Herein, the synthesis and characterization of a PAH containing three azulene units is reported via reduction and elimination of its trioxo derivative.

Truxene-Centered Electron Acceptors for Non-Fullerene Solar Cells: Alkyl Chain and Branched Arm Engineering.

A series of symmetrical truxene-centered and 3-ethylrhodanine end-capped electron acceptors with high absorption coefficient, namely Tr(Hex)6-3RD, Tr(Dec)6-3RD, and Tr(Hex)6-6RD, were prepared and constructed for non-fullerene solar cells. To satisfy solution-processability, multiple energy levels, and suitable morphology, these three acceptors were comparatively studied through alkyl chain (hexyl/decyl) and branched-arm engineering (three/six branched arms). The six-bladed propeller acceptor of Tr(Hex)6-6RD recorded the power conversion efficiency (PCE) of 1.1% blending with PTB7-Th without additional additives and post-processing. This work highly broadens the potential applications of star-shaped truxene building blocks in the fields of organic electronics.

Metallo-Supramolecular Octahedral Cages with Three Types of Chirality towards Spontaneous Resolution.

Chirality is one of the most important intrinsic properties of (supra)molecules. In this study, we obtained enantiomeric metallo-supramolecular octahedra without using any chiral sources. Such cages were self-assembled by prochiral trispyridine ligand L based on a C3h truxene core and CuII salts. Crystallization of the cages with BF4 - as counterions afforded racemate crystals; while crystallizations of cages with ClO4 - and OTf- as counterions resulted in conglomerates with spontaneous resolution. Three types of chirality were observed in each cage, including planar chirality of the truxene core, axial chirality from the pyridyl and truxene moieties, and propeller chirality of the pyridyl-CuII coordination sites. The cages reported here are among the largest discrete synthetic metallo-supramolecules ever reported with chiral self-sorting behavior. Remarkably, the chiral cages exhibited very slow racemization even at low concentrations, suggesting their high stability in solution.

Tuning the properties of truxene by successive substitution of nitrogen and sulphur heteroatoms: a DFT insight.

In this study, truxene, along with its nitrogen- and sulphur-substituted counterparts were investigated for their properties. The important characteristic properties of a potential conducting material such as HOMO-LUMO gap, electron affinity, ionization potential, and density of states were calculated and compared for analysis. Furthermore, Fukui function and dual descriptor analyses were also carried out, to identify the reactive sites in each of the molecules, as well as understand the effect of substituted heteroatoms. It was seen that the di-substituted candidates were convincingly better fitting for optoelectronic applications.

Design, synthesis and photophysical properties of novel star-shaped truxene-based heterocycles utilizing ring-closing metathesis, Clauson-Kaas, Van Leusen and Ullmann-type reactions as key tools.

Design, synthesis and properties of polycyclic aromatic hydrocarbons (PAHs) has historically attracted a considerable interdisciplinary interest from both fundamental as well as applied viewpoint on account of their wonderful optoelectronic properties. The scientific interest in two-dimensional star-shaped PAHs particularly in truxene architectures arises because of their high thermal stability, exceptional solubility and ease with which they can be constructed and modified. Therefore, bearing in mind a wide range of applications of truxene and its congeners, herein we reveal three novel distinctly different routes for the generation of C 3-symmetric pyrrole-based truxene architectures by means of cyclotrimerization, ring-closing metathesis (RCM), Clauson-Kaas and Ullmann-type coupling reactions as key steps. Moreover, we have also assembled some other interesting heterocyclic systems possessing oxazole, imidazole, benzimidazole, and benzoxazole in the framework of truxene. Additionally, the preliminary photophysical properties (absorption and emission) for these versatile systems has been revealed.

Truxene Functionalized Star-Shaped Non-fullerene Acceptor With Selenium-Annulated Perylene Diimides for Efficient Organic Solar Cells.

An electron acceptor with a truxene core and ring-fusion perylene diimide (PDI) tripolymer annulated by selenium (Se) branch, named as FTr-3PDI-Se, is designed and synthesized. FTr-3PDI-Se exhibits large conjugated planar conformation, strong absorption spectra in the regions of 300-400 and 450-550 nm, the deep HOMO energy level of 6.10 eV, and high decomposition temperature above 400°C. The FTr-3PDI-Se: PBDB-T-2Cl based device achieved a disappointing power conversion efficiency (PCE) of 1.6% together with a high V oc of 1.12 V. The low PCE was due to the large aggregates of blend film, the imbalanced hole/electron transport and low PL quenching efficiencies. The high V oc can be attributed to the high-lying LUMO level of FTr-3PDI-Se and the low-lying HOMO level of PBDB-T-2Cl. Our research presents an interesting and effective molecule-designing method to develop non-fullerene acceptor.

Photophysics, Electrochemistry and Efficient Electrochemiluminescence of Trigonal Truxene-Core Dyes.

We synthesized and characterized a series of dyes built from a spirofluorene or truxene core. The quadrupolar spirofluorene system is the initial building unit for the design and preparation of more complex star-shaped dyes consisting of a truxene core bearing three di- or triphenylamine moieties with or without a thiophene connector. Their photophysical, electrochemical, and electrochemiluminescence (ECL) properties were first investigated in solution. Structure/activity relationships were derived and rationalized by comparing the quadrupolar system and trigonal truxene-core derivatives using computational studies. The photophysical and redox characteristics are drastically tuned by the introduction of a thiophene bridge and electron-donor substituents at their terminal branches. These comparative studies show the essential role of the stability of both radical cations and anions to obtain efficient ECL dyes. The stabilization of the radicals is directly related to the charge delocalization due to the π-conjugation by the thiophene bridge. The brightest ECL is achieved by annihilation and coreactant (benzoyl peroxide) pathways with the blue-emitting truxene dye, which is 2- and 4.5-times greater than that of the quadrupolar compound and reference [Ru(bpy)3 ]2+ emitter, respectively. Such an extensive study on these extended π-conjugated molecules presenting different core structures may guide the design and synthesis of new ECL dyes with a strong efficiency.