Enhancing Magnetic Communication between Metal Centres: The Role of s-Tetrazine Based Radicals as Ligands.

Although 1,2,4,5-tetrazines or s-tetrazines have been known in the literature for more than a century, their coordination chemistry has become increasingly popular in recent years due to their unique redox activity, multiple binding sites and their various applications. The electron-poor character of the ring and stabilization of the radical anion through all four nitrogen atoms in their metal complexes provide new aspects in molecular magnetism towards the synthesis of new high performing Single Molecule Magnets (SMMs). The scope of this review is to examine the role of s-tetrazine radical ligands in transition metal and lanthanide based SMMs and provide a critical overview of the progress thus far in this field. As well, general synthetic routes and new insights for the preparation of s-tetrazines are discussed, along with their redox activity and applications in various fields. Concluding remarks along with the limitations and perspectives of these ligands are discussed.

Bis(trialkylsilyl oxide) Silicon Phthalocyanines: Understanding the Role of Solubility in Device Performance as Ternary Additives in Organic Photovoltaics.

The use of ternary additives in organic photovoltaics is a promising route for improving overall device performance. Silicon phthalocyanines (SiPcs) are ideal candidates due to their absorption profile, low cost, and ease of synthesis and chemical tunability. However, to date, only a few examples have been reported and specific strategies for aiding in the design of improved ternary additives have not been established. In this study, we report a relationship between ternary additive solubility and device performance, demonstrating that device performance is maximized when the SiPc additive solubility is similar to that of the donor polymer (P3HT, in this case). This improved performance can be attributed to the favored interfacial precipitation of the SiPc when its solubility matches that of the other components of the thin film. The power conversion efficiency (PCE) varied from 2.4% to 3.4% by using axially substituted SiPcs with different solubilities, where the best ternary additive led to a 25% increase in PCE compared to that of the baseline device.

Stark Sublevel-Based Thermometry with Tb(III) and Dy(III) Complexes Cosensitized via the 2-Amidinopyridine Ligand.

Amidine-based ligand frameworks were employed to isolate a series of mononuclear lanthanide complexes. The employed N-2-pyridylimidoyl-2-pyridylamidine (Py2ImAm) undergoes metal-assisted hydrolysis yielding the ligand 2-amidinopyridine (PyAm), which coordinates to the lanthanide ions affording [Ln(acac)3(PyAm)], where Ln = Eu(III) (1), Gd(III) (2), Tb(III) (3), Dy(III) (4) along with the Y(III) analogue (5). The Eu(III), Tb(III), and Dy(III) congeners exhibit characteristic emissions of red, green, and yellow light, respectively, with emission quantum yields of 3, 65, and 8%, respectively. Due to changes in the thermal population of the Stark sublevels, the Tb(III) and Dy(III) complexes can be used as efficient optical thermometers with maximum relative sensitivities of 1.57 and 2.03% K-1 for 3 and 4, respectively. These results demonstrate the viability of PyAm as an antenna for the sensitization of lanthanide ions.

Three-Dimensional Magnetic Exchange Networks in Trigonal Bisdithiazolyl Radicals.

The N-methyl-4-phenyl-pyridine-bridged bisdithiazolyl radical PhBPMe is polymorphic, crystallizing from cold acetonitrile in a trigonal α-phase, space group P3121, and from hot dichloroethane in an orthorhombic ß-phase, space group Pca21. The crystal structures of both phases consist of slipped π-stacks of undimerized radicals aligned laterally into herringbone arrays. In the ß-phase, there are two independent radicals in the asymmetric unit, and the resulting π-stacks form corrugated layers interspersed by methyl and phenyl groups which block the approach of neighboring radicals. In the α-phase, the methyl/phenyl groups and the radical π-stacks separately form spirals about 31 axes, the latter giving rise to a 3D network of close radical/radical contacts. Variable temperature magnetic susceptibility measurements on the ß-phase indicate strong antiferromagnetic coupling. Weaker but predominantly antiferromagnetic interactions (θ = -20.7 K) are observed in the α-phase. A high temperature series expansion analysis of the magnetic data for the α-phase affords antiferromagnetic exchange energies for the one- and two-step radical/radical interactions about the 31 spirals ( J1 = -1.2 K, J2 = -10.9 K, respectively), with weak ferromagnetic interactions along the π-stacks ( Jπ = +1.8 K). Despite the presence of a 3D network based on the dominant J2 interactions, which affords two independent bipartite sublattices, no evidence of bulk antiferromagnetic order has been observed above T = 2 K. The magnetic results are discussed in light of exchange energies calculated using density functional theory broken symmetry methods.

Halide Influence on Molecular and Supramolecular Arrangements of Iron Complexes with a 3,5-Bis(2-Pyridyl)-1,2,4,6-Thiatriazine Ligand.

A series of iron centered complexes, namely, [Fe(Py2TTA)Cl2] (1), [Fe(Py2TTA)Br2] (2), and [Fe(µ-F)(Py2TTAO)F]∞ (3), were isolated via complexation of 3,5-bis(2-pyridyl)-1,2,4,6-thiatriazine (Py2TTAH) with various ferric halides (e.g., FeF3, FeCl3, and FeBr3). Comparison of the optical and electrochemical spectroscopy, structural analysis, and magnetic studies reveal numerous similarities between the chlorido (1) and bromido (2) derivatives, which crystallize as discrete five-coordinate iron centered complexes with coordination geometries that are intermediate between trigonal bipyramidal and square base pyramid. Conversely, the fluorido derivative (3) results in a completely different structure due to oxidation of the ligand and the formation of a one-dimensional coordination polymer held together through a bridging fluoride ion. Consequently, the spectroscopic and magnetic behavior of 3 differs significantly compared with 1 and 2. Complexes 1 and 2 exhibit paramagnetic properties typical for a mononuclear S = 5/2 system with weak intermolecular antiferromagnetic interactions at low temperatures, whereas complex 3 demonstrates significant exchange couplings within the chain and weak antiferromagnetic interchain interactions, which stabilize a canted antiferromagnetic state below 4.2 K.

Low-Cost Silicon Phthalocyanine as a Non-Fullerene Acceptor for Flexible Large Area Organic Photovoltaics.

We demonstrate large-area (1 cm2) organic photovoltaic (OPVs) devices based on bis(tri-n-butylsilyl oxide) silicon phthalocyanine (3BS)2-SiPc as a non-fullerene acceptor (NFA) with low synthetic complexity paired with poly(3-hexylthiophene) (P3HT) as a donor polymer. Environment-friendly nonhalogenated solvents were used to process large area OPVs on flexible indium tin oxide (ITO)-coated polyethylene terephthalate (PET) substrates. An alternate sequentially (Alt-Sq) blade-coated active layer with bulk heterojunction-like morphology is obtained when using (3BS)2-SiPc processing with o-xylene/1,3,5-trimethylbenzene solvents. The sequential (Sq) active layer is prepared by first blade-coating (3BS)2-SiPc solution followed by P3HT coated on the top without any post-treatment. The conventional sequentially (Sq) blade-coated active layer presents very low performance due to the (3BS)2-SiPc bottom layer being partially washed off by processing the top layer of P3HT. In contrast, alternate sequentially (Alt-Sq) blade-coated layer-by-layer film shows even better device performance compared to the bulk heterojunction (BHJ) active layer. Time-of-flight secondary ion mass spectroscopy (TOF-SIMS) and atomic force microscopy (AFM) reveal that the Alt-Sq processing of the active layer leads to a BHJ-like morphology with a well-intermixed donor-acceptor component in the active layer while providing a simpler processing approach to low-cost and large-scale OPV production.

Variance-resistant PTB7 and axially-substituted silicon phthalocyanines as active materials for high-Voc organic photovoltaics.

While the efficiency of organic photovoltaics (OPVs) has improved drastically in the past decade, such devices rely on exorbitantly expensive materials that are unfeasible for commercial applications. Moreover, examples of high voltage single-junction devices, which are necessary for several applications, particularly low-power electronics and rechargeable batteries, are lacking in literature. Alternatively, silicon phthalocyanines (R2-SiPc) are inexpensive, industrially scalable organic semiconductors, having a minimal synthetic complexity (SC) index, and are capable of producing high voltages when used as acceptors in OPVs. In the present work, we have developed high voltage OPVs composed of poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno [3,4 b]thiophenediyl}) (PTB7) and an SiPc derivative ((3BS)2-SiPc). While changes to the solvent system had a strong effect on performance, interestingly, the PTB7:(3BS)2-SiPc active layer were robust to spin speed, annealing and components ratio. This invariance is a desirable characteristic for industrial production. All PTB7:(3BS)2-SiPc devices produced high open circuit voltages between 1.0 and 1.07 V, while maintaining 80% of the overall efficiency, when compared to their fullerene-based counterpart.

Probing optical and magnetic properties via subtle stereoelectronic effects in mononuclear DyIII-complexes.

Tapping into the secondary coordination environment of mononuclear DyIII-complexes leads to drastic changes in luminescence and magnetism. Visualization of effects induced by stereoelectronics on the opto-magnetic properties was achieved through subtle modifications in the ligand framework.

Thin-Film Engineering of Solution-Processable n-Type Silicon Phthalocyanines for Organic Thin-Film Transistors.

Metal and metalloid phthalocyanines are an abundant and established class of materials widely used in the dye and pigment industry as well as in commercial photoreceptors. Silicon phthalocyanines (SiPcs) are among the highest-performing n-type semiconductor materials in this family when used in organic thin-film transistors (OTFTs) as their performance and solid-state arrangement are often increased through axial substitution. Herein, we study eight axially substituted SiPcs and their integration into solution-processed n-type OTFTs. Electrical characterization of the OTFTs, combined with atomic force microscopy (AFM), determined that the length of the alkyl chain affects device performance and thin-film morphology. The effects of high-temperature annealing and spin coating time on film formation, two key processing steps for fabrication of OTFTs, were investigated by grazing-incidence wide-angle X-ray scattering (GIWAXS) and X-ray diffraction (XRD) to elucidate the relationship between thin-film microstructure and device performance. Thermal annealing was shown to change both film crystallinity and SiPc molecular orientation relative to the substrate surface. Spin time affected film crystallinity, morphology, and interplanar d-spacing, thus ultimately modifying device performance. Of the eight materials studied, bis(tri-n-butylsilyl oxide) SiPc exhibited the greatest electron field-effect mobility (0.028 cm2 V-1 s-1, a threshold voltage of 17.6 V) of all reported solution-processed SiPc derivatives.

Developing and Comparing 2,6-Anthracene Derivatives: Optical, Electrochemical, Thermal, and Their Use in Organic Thin Film Transistors.

Anthracene-based semiconductors have attracted great interest due to their molecular planarity, ambient and thermal stability, tunable frontier molecular orbitals and strong intermolecular interactions that can lead to good device field-effect transistor performance. In this study, we report the synthesis of six anthracene derivatives which were di-substituted at the 2,6-positions, their optical, electrochemical and thermal properties, and their single crystal structures. It was found that 2,6-functionalization with various fluorinated phenyl derivatives led to negligible changes in the optical behaviour while influencing the electrochemical properties. Furthermore, the choice of fluorinated phenyl moiety had noticeable effects on melting point and thermal stability (ΔTm < 55 °C and ΔTd < 65 °C). Bottom-gate top-contact (BGTC) organic thin transistors (OTFTs) were fabricated and characterized using the 2,6-anthracene derivatives as the semiconducting layer. The addition of fluorine groups on the phenyl groups led to a transition from p-type behaviour to n-type behaviour in BGBC OTFTs.

Old Molecule, New Chemistry: Exploring Silicon Phthalocyanines as Emerging N-Type Materials in Organic Electronics.

Efficient synthesis of silicon phthalocyanines (SiPc) eliminating the strenuous reaction conditions and hazardous reagents required by classical methods is described. Implementation into organic thin-film transistors (OTFTs) affords average electron field-effect mobility of 3.1 × 10-3 cm2 V-1 s-1 and threshold voltage of 25.6 V for all synthetic routes. These results demonstrate that our novel chemistry can lead to high performing SiPc-based n-type OTFTs.

Developing 9,10-anthracene Derivatives: Optical, Electrochemical, Thermal, and Electrical Characterization.

Anthracene-based semiconductors are a class of molecules that have attracted interest due to their air stability, planarity, potential for strong intermolecular interactions, and favorable frontier molecular orbital energy levels. In this study seven novel 9,10-anthracene-based molecules were synthesized and their optical, electrochemical, and thermal properties were characterized, along with their single crystal arrangement. We found that functionalization of the 9,10-positions with different phenyl derivatives resulted in negligible variation in the optical properties with minor (±0.10 eV) changes in electrochemical behavior, while the choice of phenyl derivative greatly affected the thermal stability (Td > 258 °C). Preliminary organic thin film transistors (OTFTs) were fabricated and characterized using the 9,10-anthracene-based molecules as the semiconductor layer. These findings suggest that functionalization of the 9,10-position of anthracene leads to an effective handle for tuning of the thermal stability, while having little to no effect on the optical properties and the solid-state arrangement.

Ferromagnetically coupled dinuclear MII complexes based on a boratriazine ligand framework.

A boratriazine ligand, which incorporates attractive features from both bodipy and terpy, has been used to synthesize [Fe2II(µ1,1-N3)2(Py2F2BTA)2(N3)2] (1) and [Co2II(µ1,1-N3)2(Py2F2BTA)2(N3)2] (2). Both 1 and 2 feature a double end-on azido bridging motif, which promotes ferromagnetic interactions between the metal centres. Indeed, 1 represents the first report of a dinuclear FeII complex with this bridging mode exhibiting J = 5.7(9) cm-1 and D = -6.0(4) cm-1, while the isostructural Co analogue shows J = 7.1(9) cm-1 and D = 17.3(9) cm-1.

Spin-canting in heavy atom heterocyclic radicals.

A pair of isostructural bis-selenathiazolyl and bis-diselenazolyl radical conductors display weak (spin-canted) ferromagnetism with Tc values of 18 K and 27 K respectively.

Organic Thin Film Transistors Incorporating Solution Processable Thieno[3,2-b]thiophene Thienoacenes.

Bottom-gate bottom-contact organic thin film transistors (OTFTs) were prepared with four novel star-shaped conjugated molecules containing a fused thieno[3,2-b]thiophene moiety incorporated either in the core and/or at the periphery of the molecular framework. The molecules were soluble in CS2, allowing for solution-processing techniques to be employed. OTFTs with different channel geometries were characterized in both air and vacuum in order to compare environmental effects on performance. Blending the small molecules with poly(styrene), an insulating polymer, facilitated the formation of an even semiconducting film, resulting in an order of magnitude increase in device mobility. The highest field-effect mobilities were in air and on the order of 10-3 cm²/Vs for three of the four molecules, with a maximum mobility of 9.2 × 10-3 cm²/Vs achieved for the most conjugated small molecule. This study explores the relationship between processing conditions and OTFT devices performance for four different molecules within this new family of materials, resulting in a deeper insight into their potential as solution-processable semiconductors.

Connecting mononuclear dysprosium single-molecule magnets to form dinuclear complexes via in situ ligand oxidation.

A Dy2 complex, exhibiting SMM behaviour, and its Y analogue were prepared via in situ oxidation of Py2TTA, a pincer type ligand, followed by dimerisation. This unique metal complexation and subsequent dimerization were followed by solution NMR studies.

Bis-1,2,3-thiaselenazolyl radicals and their sigma-bonded dimers.

Resonance stabilized bis-1,2,3-thiaselenazolyl radicals associate in the solid state to afford Se-Se sigma-bonded dimers.

The effect of selenium incorporation on the bandwidth and conductivity of neutral radical conductors.

The first example of an undimerized pi-stacked bis-1,2,3-thiaselenazolyl radical displays improved bandwidth and conductivity relative to an isostructural bis-1,2,3-dithiazolyl.

Anion-induced Ag(I) self-assemblies with electron deficient aromatic ligands: anion-π-system interactions as a driving force for templated coordination networks.

Three novel 1D, 2D and 3D coordination polymers were successfully isolated using nitrogen based 3,6-bis(2'-pyrimidyl)-1,2,4,5-tetrazine (BPymTz) and 2,4,6-tris(2-pyrimidyl)-1,3,5-triazine (TPymT) ligands with Ag(I) ions. The formation of these supramolecular assemblies was templated through anion-π-system interactions.

Ambivalent binding between a radical-based pincer ligand and iron.

A complex exhibiting valence delocalization was prepared from 3,5-bis(2-pyridyl)-1,2,4,6-thiatriazinyl (), an inherently redox active pincer-type ligand, coordinated to iron ( ()). Complex can be prepared via two routes, either from the reaction of the neutral radical with FeCl2 or by treatment of the anionic ligand () with FeCl3, demonstrating its unique redox behaviour. Electrochemical studies, solution absorption and solid-state diffuse reflectance measurements along with X-ray crystallography were carried out to elucidate the molecular and solid-state properties. Temperature- and field-dependent Mössbauer spectroscopy coupled with magnetic measurements revealed that exhibits an isolated S = 5/2 ground spin state for which the low-temperature magnetic behaviour is dominated by exchange interactions between neighbouring molecules. This ground state is rationalized on the basis of DFT calculations that predict the presence of strong electronic interactions between the redox active ligand and metal. This interaction leads to the delocalization of ß electron density over the two redox active centres and highlights the difficulty in assigning formal charges to .