Georgia A. Zissimou

A magnetostructural investigation of an abrupt spin transition for 1-phenyl-3-trifluoromethyl-1,4-dihydrobenzo[e][1,2,4]triazin-4-yl

1-Phenyl-3-trifluoromethyl-1,4-dihydrobenzo[e][1,2,4]triazin-4-yl is the first example of a hydrazyl radical that shows a reversible sharp spin transition fully completed within 5(1) K. The nominally first-order transition takes place at ca. 58(2) K and proceeds via subtle changes of intra- and interstack interactions between two similar structural phases. The low-temperature phase (5-60 K) is diamagnetic and has a singlet ground state (2Jexp = -166.8 cm(-1), gsolid = 2.0042, ρ = 0.2%) stemming from a multicenter two-electron interaction. The high-temperature phase (60-300 K) is paramagnetic as a result of noninteracting S = 1/2 spins arising from weakly bound dimers.

Novel BODIPY-based conjugated polymers donors for organic photovoltaic applications

Five new polymers based on the 4,4′-difluoro-4-bora-3a,4a-diaza-s-indacene core (BODIPY) chromophore moiety have been synthesized as low bandgap polymers for optoelectronic applications. The polymers exhibited high solubility in common organic solvents and optical bandgaps ranging from 1.7–2 eV. The materials were characterized using NMR, UV-Vis, steady state and time-resolved photoluminescence and the energy levels were examined using electrochemistry and validated using quantum chemical calculations. Finally, a representative BODIPY derivative : PCBM blend was examined in terms of photovoltaic properties. Preliminary device performance parameters as a function of photo-active layer thickness and composition are reported and discussed, relating to power conversion efficiency values.

Coordination Complexes of a Neutral 1,2,4-Benzotriazinyl Radical Ligand: Synthesis, Molecular and Electronic Structures, and Magnetic Properties

A series of d-block metal complexes of the recently reported coordinating neutral radical ligand 1-phenyl-3-(pyrid-2-yl)-1,4-dihydro-1,2,4-benzotriazin-4-yl (1) was synthesized. The investigated systems contain the benzotriazinyl radical 1 coordinated to a divalent metal cation, Mn(II) , Fe(II) , Co(II) , or Ni(II) , with 1,1,1,5,5,5-hexafluoroacetylacetonato (hfac) as the auxiliary ligand of choice. The synthesized complexes were fully characterized by single-crystal X-ray diffraction, magnetic susceptibility measurements, and electronic structure calculations. The complexes [Mn(1)(hfac)2 ] and [Fe(1)(hfac)2 ] displayed antiferromagnetic coupling between the unpaired electrons of the ligand and the metal cation, whereas the interaction was found to be ferromagnetic in the analogous Ni(II) complex [Ni(1)(hfac)2 ]. The magnetic properties of the complex [Co(1)(hfac)2 ] were difficult to interpret owing to significant spin-orbit coupling inherent to octahedral high-spin Co(II) metal ion. As a whole, the reported data clearly demonstrated the favorable coordinating properties of the radical 1, which, together with its stability and structural tunability, make it an excellent new building block for establishing more complex metal-radical architectures with interesting magnetic properties.

4H-1,2,6-Thiadiazin-4-one-containing small molecule donors and additive effects on their performance in solution-processed organic solar cells

The optical, electrochemical, morphological and transport properties of a series of thiadiazinone (acceptor) and (thienyl)carbazoles (donor) containing π-extended donor–acceptor–donors (D–A–D) are presented. Systematic variations in the number of the thienyl units, the choice of branched or straight alkyl side chains and the use of a processing additive demonstrate their use as electron donors in bulk heterojunction solar cells blended with fullerene acceptors. The best power conversion efficiency (PCE) of 2.7% is achieved by adding to the D–A–D 3 : fullerene blend a polydimethylsiloxane (PDMS) additive, that improves the morphology and doubles the hole mobility within the D–A–D : fullerene blend.

Tetraphenylhexaazaanthracenes: 16π Weakly Antiaromatic Species with Singlet Ground States

Tetraphenylhexaazaanthracene, TPHA-1, is a fluorescent zwitterionic biscyanine with a closed-shell singlet ground state. TPHA-1 overcomes its weak 16π antiaromaticity by partitioning its π system into 6π positive and 10π negative cyanines. The synthesis of TPHA-1 is low yielding and accompanied by two analogous TPHA isomers: the deep red, non-charge-separated, quinoidal TPHA-2, and the deep green TPHA-3 that partitions into two equal but oppositely charged 8π cyanines. The three TPHA isomers are compared.

Preparation of Blatter Radicals via Aza-Wittig Chemistry: The Reaction of N-Aryliminophosphoranes with 1-(Het)aroyl-2-aryldiazenes

Reacting N-aryliminophosphoranes with 1-(het)aroyl-2-aryldiazenes in preheated diphenyl ether at ca. 150-250 °C for 5-25 min affords in most cases the 1,3-diaryl-1,4-dihydrobenzo[e][1,2,4]triazin-4-yls (aka Blatter radicals) in moderate to good yields. All new compounds are fully characterized, including EPR and CV studies for the radicals. Single-crystal X-ray structures of 1-benzoyl-2-(perfluorophenyl)diazene and 1-(perfluorophenyl)-3-phenyl-1,4-dihydrobenzo[e][1,2,4]triazinyl are also presented.

Discovery of anti-cancer activity for benzo[1,2,4]triazin-7-ones: Very strong correlation to pleurotin and thioredoxin reductase inhibition.

The thioredoxin (Trx)-thioredoxin reductase (TrxR) system plays a key role in maintaining the cellular redox balance with Trx being over-expressed in a number of cancers. Inhibition of TrxR is an important strategy for anti-cancer drug discovery. The natural product pleurotin is a well-known irreversible inhibitor of TrxR. The cytotoxicity data for benzo[1,2,4]triazin-7-ones showed very strong correlation (Pearson correlation coefficients ∼0.8) to pleurotin using National Cancer Institute COMPARE analysis. A new 3-CF3 substituted benzo[1,2,4]triazin-7-one gave submicromolar inhibition of TrxR, although the parent compound 1,3-diphenylbenzo[1,2,4]triazin-7-one was more cytotoxic against cancer cell lines. Benzo[1,2,4]triazin-7-ones exhibited different types of reversible inhibition of TrxR, and cyclic voltammetry showed characteristic quasi-reversible redox processes. Cell viability studies indicated strong dependence of cytotoxicity on substitution at the 6-position of the 1,3-diphenylbenzo[1,2,4]triazin-7-one ring.

Emission from the stable Blatter radical

1,3-Diaryl-1,4-dihydro-1,2,4-benzotriazin-4-yls are air stable organic radicals which have been exploited for their interesting magnetic properties. Herein, we present the optical properties of the “parent” radical namely 1,3-diphenyl-1,4-dihydro-1,2,4-benzotriazin-4-yl (aka “the Blatter radical”), which possesses absorption bands that span the UV and visible spectrum that lead to broadband emission across the same spectral region. As shown in our experiments, the emission originates from excited electronic states of the radical, with, however, low quantum yield. Emission across the visible is also observed from thin films of the radical when inserted into PMMA matrices. As radical concentration within the polymer matrix is increased, systematic modifications in the spectral and temporal characteristics of the fluorescence indicate the formation of radical ground state aggregates.

The Suppression of Columnar π-Stacking in 3-Adamantyl-1-phenyl-1,4-dihydrobenzo[e][1,2,4]triazin-4-yl

3-Adamantyl-1-phenyl-1,4-dihydrobenzo[e][1,2,4]triazin-4-yl (4) crystallizes as chains of radicals where the spin bearing benzotriazinyl moieties are isolated from each other. Magnetic susceptibility studies in the 5–300 K temperature region indicate that radical 4 demonstrates typical paramagnetic behavior stemming from non-interacting S = ½ spins.

Correction to Route to Benzo- and Pyrido-Fused 1,2,4-Triazinyl Radicals via N′-(Het)aryl-N′-[2-nitro(het)aryl]hydrazides

As such, Scheme 7 in the original article should now be as follows: Furthermore, the Experimental Section (section 4.7.2) now becomes: 4.7.2. 5-[1,3-Di(pyrid-2-yl)-7-(tri f luoromethyl)-1,4dihydrobenzo[e][1,2,4]triazin-4-yl]-1,3-di(pyrid-2-yl)-7-(trif luoromethyl)-1,4-dihydro-1,2,4-benzotriazin-4-yl (1o). To a stirred solution of 1,3-di(pyrid-2-yl)-7-(trifluoromethyl)-1,4-dihydro1,2,4-benzotriazine (23c) (355 mg, 1.0 mmol) in DCM (10 mL) at ca. 20 °C was added MnO2 (869 mg, 10.0 mmol). After 2 days, the reaction mixture was filtered through Celite and rinsed with additional DCM, and volatiles were removed in vacuo. The residue was chromatographed on basic alumina (DCM/t-BuOMe, 1:1) to give the title compound 1o (173 mg, 49%) as black needles. Mp (DSC) onset 218.1 °C, peak max 222.9 °C (from MeCN); Rf 0.49 (Al2O3, DCM); (found C, 60.93; H, 3.07; N, 19.89. C36H21F6N10• requires C, 61.11; H, 2.99; N, 19.79%); λmax(DCM)/nm 236 (log ε 4.56), 267 (4.66), 282 inf (4.63), 328 inf (4.36), 436 (3.78), 510 (3.31); νmax/cm −1 3061w and 3011w (Ar CH), 1585m, 1568w, 1514w, 1466m, 1429s, 1402m, 1375m, 1344s, 1325s, 1290m, 1271s, 1233w, 1190w, 1161s, 1115s, 1088m, 1061m, 1043w, 991w, 947w, 912m, 878m, 822m, 800m, 775m, 743m, 733w; MALDITOF (m/z) 709 (MH + 1, 39%), 708 (MH, 100), 696 (24), 630 (8), 617 (20), 603 (9), 588 (17), 354 (8), 342 (9), 339 (6). The structures of the remaining radicals have been rechecked, and their structures are correct. From a brief initial study, it appears that the higher basicity of the dipyridyl 1o is partly responsible for this unexpected dimerization, and we have been unable to find conditions to oxidize the precursor triazine 23c that do not give the dimeric species 1o. This dimerization is now under study, and we plan to provide a full report on this reaction in the very near future.