Molecular crystal assembly of organic radicals and biradicals

Magnetostructural investigations were carried out on pyrene-1-yl (Pyr) bearing nitronylnitroxide (NN) and iminoylnitroxide (IN) radicals. PyrNN gives two allotropes: one has spin-paired dyads with ΔE = J/k ≈ -178 K, and the other is only half spin-paired with ΔE = J/k ≈ -102 K and the other half paramagnetic. PyrIN also gives two allotropes, an anti conformation that is spin paired in the crystal lattice with ΔE = J/k = -410 K, and a syn conformation that is disordered and paramagnetic. PyrNN also was discovered to co-crystallize with C6F6 in 2:1 ratio to give chains of radical networks linked into networks exhibiting low dimensional 1-D or 2-D antiferromagnetic exchange behavior. Furthermore, PyrNN was discovered to form a 2:1:2 co-crystal with octafluoronaphthalene (OFN) and entrapped solvent dichloromethane (DCM), in which the radical is ``shepherded\u27\u27 into forming chains of radical-radical contacts on the peripheries of (PyrNN-OFN-PyrNN)n pi-stacks, giving weak, low dimensional inter-radical antiferromagnetic (AFM) exchange interactions. Anthraquinone-substituted nitronylnitroxide radical (AntQNN) was synthesized and found to form two crystal polymorphs. Magnetostructural investigations carried on these indicated that both have antiferromagnetic (AFM) exchange behavior attributed to chain-type inter-radical contacts: one with J1D/k ≈ -3 K, and one with J1D/k ≈-17 K. Five different anthracene nitroxide-type biradicals were synthesized: 27AntdNN, 27AntdIN, 26AntdNN, 26AntdIN, and 9Br27AntdNN. Room temperature solution state, and frozen solution state electron spin resonance (ESR) studies were carried on all of these biradicals. Crystallographic packing information was successfully obtained for 27AntdIN, 26AntdNN, 26AntdIN, and 9Br27AntdNN. Magnetic susceptibility measurements were carried on 27AntdNN, 27AntdIN, 26AntdIN and 9Br27AntdNN. The NN derivatives showed both ferromagnetic (presumed intramolecular) and antiferromagnetic exchange interactions in the solid state. Four different anthraquinone nitroxide-type biradicals were synthesized: 27AntQdNN, 27AntQdIN, 26AntQdNN, 26AntdIN. ESR studies were carried on these biradicals, and showed that 27AntQdNN is not a stable organic radical. While ESR spectra confirmed that 27AntQdNN, 27AntQdIN are biradicals, ESR spectra with isolated monoradical behavior were obtained for 26AntQdNN, 26AntQdIN. Iodine substituted meta-phenylene nitroxide biradicals, IPhdNN, IPhNNIN, and IPhdIN were synthesized. Room temperature and frozen solution ESR studies showed triplet states with strong intramolecular spin interaction. Magnetic behavior and crystallography for IPhdIN (which incorporates DCM), showed halogen bonding between molecules that assists formation of chains between radical sites

Poly((2-alkylbenzo[1,2,3]triazole-4,7-diyl)vinylene)s for Organic Solar Cells

Poly((2-Alkylbenzo[1,2,3]triazole-4,7-diyl)vinylene)s (pBTzVs) synthesized by Stille coupling show different absorption spectra, solid-state morphology, and photovoltaic performance, depending on straight-chain versus branched-chain (pBTzV12 and pBTzV20) pendant substitution. Periodic boundary condition density functional computations show limited alkyl pendant effects on isolated chain electronic properties; however, pendants could influence polymer backbone conjugative planarity and polymer solid film packing. The polymers are electronically ambipolar, with best performance by pBTzV12 with hole and electron transport mobilities of 4.86 x 10(-6) and 1.96 x 10(-6) cm(2) V-1 s(-1), respectively. pBTzV12 gives a smooth film morphology, whereas pBTzV20 gives a very different fibrillar morphology. For ITO/PEDOT:PSS/(1:1 w/w polymer: PC71BM)/LiF/Al devices, pBTzV12 gives power conversion efficiency (PCE) up to 2.87%, and pBTzV20 gives up to PCE = 1.40%; both have open-circuit voltages of V-OC=0.6-0.7 V. (C) 2015 Wiley Periodicals, Inc

Rigid Core Anthracene and Anthraquinone Linked Nitronyl and Iminoyl Nitroxide Biradicals

The first syntheses of bis­(nitronyl nitroxide) and bis­(iminoyl nitroxide) (diNN, diIN) biradicals linked through rigid acene core conjugating anthracene (A) and anthraquinone (AQ) units are reported. Computational modeling predicts weak intramolecular exchange in AQ-linked systems, but A-linked biradicals to have ground state multiplicities consistent with the Borden-Davidson disjointness model. Solution electron spin resonance spectra showed inter-radical exchange-coupled triplet states, except for 2,6-AQ biradicals showing isolated spin spectra. Crystallography of the A-linked biradicals shows a key role for inter-radical contacts for molecular packing. DiINs showed lower-dimensional dyad packing with disorder at the radical units: the conformationally more symmetrical diNNs gave staircase one-dimensional or brickwork two-dimensional lattices. Core anthracene unit stacking was only seen in two systems with bromine on the central anthracene ring: the (large) bromine occupies alternate side placement in dyad stacks for the diIN, chain stacks for the diNN. Magnetism of 2,7-A-linked systems showed predominant ferromagnetic intramolecular triplet-singlet splitting of 24–28 K for diNNs and 8 K for diINs, plus weak antiferromagnetic (AFM) interactions from intermolecular contacts. The 2,6-A-linked biradicals showed AFM exchange between spins. Both A and AQ cores offer possibilities for electronic material development, with a combination of multiple radical spins and π-electron-rich acene cores

Magnetic Mn and Co Complexes with a Large Polycyclic Aromatic Substituted Nitronylnitroxide

2-(1′-Pyrenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1<i>H</i>-imidazole-3-oxide-1-oxyl (PyrNN) was reacted with M­(hfac)₂ (M = Mn­(II) and Co­(II), hfac = hexafluoracetylacetonate) to give two isostructural ML₂ stoichiometry M­(hfac)₂(PyrNN)₂ complexes and a ML stoichiometry one-dimensional (1-D) polymer chain complex [Mn­(hfac)₂(PyrNN)]. The ML₂ complexes have similar crystal structures with monoclinic unit cells, in which one NO unit from each PyrNN ligand is bonded to the transition metal on cis vertices of a distorted octahedron. The major magnetic interactions are intracomplex metal-to-radical exchange (<i>J</i>), and intermolecular exchange across a close contact between the uncoordinated NO units (<i>J</i>′). For M = Mn­(II) an approximate chain model fit gives <i>g</i> = 2.0, <i>J</i> = (−)­125 cm^–1 and <i>J</i>′ = (−)­49 cm^–1; for M = Co­(II), <i>g</i> = 2.4, <i>J</i> = (−)­180 cm^–1, and <i>J</i>′ = (−)­70 cm^–1. Hybrid density functional theory (DFT) computations modeling the intermolecular exchange by using only the radical units across the close contact are in good accord with the estimated values of <i>J</i>′. The chain type complex structure shows solvent incorporation for overall structure [Mn­(hfac)₂(PyrNN)]_<i>n</i>·0.5­(CHCl₃)·0.5­(C₇H₁₆). Both NO groups of the PyrNN ligand are complexed to form helical chains, with very strong metal to radical antiferromagnetic exchange that gives overall ferrimagnetic behavior

Magnetic Mn and Co Complexes with a Large Polycyclic Aromatic Substituted Nitronylnitroxide

2-(1′-Pyrenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1<i>H</i>-imidazole-3-oxide-1-oxyl (PyrNN) was reacted with M­(hfac)₂ (M = Mn­(II) and Co­(II), hfac = hexafluoracetylacetonate) to give two isostructural ML₂ stoichiometry M­(hfac)₂(PyrNN)₂ complexes and a ML stoichiometry one-dimensional (1-D) polymer chain complex [Mn­(hfac)₂(PyrNN)]. The ML₂ complexes have similar crystal structures with monoclinic unit cells, in which one NO unit from each PyrNN ligand is bonded to the transition metal on cis vertices of a distorted octahedron. The major magnetic interactions are intracomplex metal-to-radical exchange (<i>J</i>), and intermolecular exchange across a close contact between the uncoordinated NO units (<i>J</i>′). For M = Mn­(II) an approximate chain model fit gives <i>g</i> = 2.0, <i>J</i> = (−)­125 cm^–1 and <i>J</i>′ = (−)­49 cm^–1; for M = Co­(II), <i>g</i> = 2.4, <i>J</i> = (−)­180 cm^–1, and <i>J</i>′ = (−)­70 cm^–1. Hybrid density functional theory (DFT) computations modeling the intermolecular exchange by using only the radical units across the close contact are in good accord with the estimated values of <i>J</i>′. The chain type complex structure shows solvent incorporation for overall structure [Mn­(hfac)₂(PyrNN)]_<i>n</i>·0.5­(CHCl₃)·0.5­(C₇H₁₆). Both NO groups of the PyrNN ligand are complexed to form helical chains, with very strong metal to radical antiferromagnetic exchange that gives overall ferrimagnetic behavior

Sensing of proteins in human serum using conjugates of nanoparticles and green fluorescent protein

There is a direct correlation between protein levels and disease states in human serum, which makes it an attractive target for sensors and diagnostics. However, this is challenging because serum features more than 20,000 proteins, with an overall protein content greater than 1 mM. Here we report a sensor based on a hybrid synthetic–biomolecule that uses arrays of green fluorescent protein and nanoparticles to detect proteins at biorelevant concentrations in both buffer and human serum. Distinct and reproducible fluorescence-response patterns were obtained from five serum proteins (human serum albumin, immunoglobulin G, transferrin, fibrinogen and α-antitrypsin), both in buffer and when spiked into human serum. Using linear discriminant analysis we identified these proteins with an identification accuracy of 100% in buffer and 97% in human serum. The arrays were also able to discriminate between different concentrations of the same protein, as well as a mixture of different proteins in human seru