Charge Delocalization in a Cyclometalated Bisruthenium Complex Bridged by a Noninnocent 1,2,4,5-Tetra(2-pyridyl)benzene Ligand

Two ruthenium atoms are covalently connected to the para positions of a phenyl ring in 1,2,4,5-tetra(2-pyridyl)benzene (tpb) to form a linear Ru–tpb–Ru arrangement. This unique structure leads to appealing electronic properties for the biscyclometalated complex [(tpy)Ru(tpb)Ru(tpy)]2+, where tpy is 2,2′;6′,2″-terpyridine. It could be stepwise oxidized at substantially low potential (+0.12 and +0.55 V vs Ag/AgCl) and with a noticeably large comproportionation constant (1.94 × 107). In addition to the routinely observed metal-to-ligand charge-transfer transitions, [(tpy)Ru(tpb)Ru(tpy)]2+ displays a separate and distinct absorption band at 805 nm with appreciable absorptivity (ε = 9000 M–1 cm–1). This band is assigned to the charge transition from the Ru–tpb–Ru motif to the pyridine rings of tpb with the aide of density functional theory (DFT) and time-dependent DFT calculations. Complex [(tpy)Ru(tpb)Ru(tpy)]2+ was precisely titrated with 1 equiv of cerium ammonium nitrate to produce [(tpy)Ru(tpb)Ru(tpy)]3+, which shows intense multiple NIR transitions. The electronic coupling parameters Hab of individual NIR components are determined to be 5812, 4942, 4358, and 3560 cm–1. DFT and TDDFT calculation were performed on [(tpy)Ru(tpb)Ru(tpy)]3+ to elucidate its electronic structure and spin density population and the nature of the observed NIR transitions. Electron paramagnetic resonance studies of [(tpy)Ru(tpb)Ru(tpy)]3+ exhibit a discernible rhombic signal with the isotropic g factor of ⟨g⟩ = 2.144. These results point to the strong orbital interaction of tpb with metal centers and that tpb behaves as a redox noninnocent bridging ligand in [(tpy)Ru(tpb)Ru(tpy)]2+. Complex [(tpy)Ru(tpb)Ru(tpy)]3+ is determined to be a Robin–Day class III system with full charge delocalization across the Ru–tpb–Ru motif

Solvent-Assisted Self-Assembly of Fullerene into Single-Crystal Ultrathin Microribbons as Highly Sensitive UV–Visible Photodetectors

The size, shape, and crystallinity of organic nanostructures play an important role in their physical properties and are mainly determined by the self-assembling kinetics of molecular components often involving the solvent conditions. Here, we reported a kinetically controlled self-assembly of C₆₀ assisted by the solvent carbon bisulfide (CS₂) into single-crystal ultrathin microribbons of 2C₆₀·3CS₂, upon mixing the poor solvent isopropyl alcohol with a C₆₀/CS₂ stock solution. Surface energy calculations reveal that these microribbons represent a kinetically favored high-energy state as compared with the thermodynamically stable shape of prismatic rods. High-resolution transmission electron microscopy observations clarify that association of CS₂ at the nucleation stage helps to guide and rigidify the formation of π–π stacking 1D chains of C₆₀ through the surrounding CS₂ cage-like structures, which further act as glue, boosting lateral assembly of as-formed 1D chains into untrathin 2D microribbon single crystals. Precise control over the thickness, width, and length of 2C₆₀·3CS₂ microribbons was achieved by manipulation of the growth kinetics through adjusting the solvent conditions. Upon heating to 120 °C, sublimation of CS₂ components results in fcc C₆₀ microribbons. We found that both microribbons of solvated monoclinic 2C₆₀·3CS₂ and pure fcc C₆₀ exhibit highly sensitive photoconductivity properties with a spectral response range covering UV to visible. The highest on/off ratio of two-terminal photodetectors based on single ribbons reaches around 250, while the responsitivity is about 75.3 A W^–1 in the UV region and 90.4 A W^–1 in the visible region

Theoretical Study of Tetrahydrofuran-Stabilized Al₁₃ Superatom Cluster

We present here an in-depth study upon the interaction between a neutral cluster Al13 and a typical ligand tetrahydrofuran (THF) via density functional theory (DFT) calculation. It is found that electron delocalization over the framework of Al13 and THF facilitates ligand-to-Al13 charge transfer leading to enhanced stability for the superhalogen cluster Al13. Further study on the stabilization of Al13(THF)n cluster complexes with n = 1–8 reveals that the adsorption of more THF ligands gradually enhances the total binding energy and the total electronic charge transfer from the ligand to Al13. The bonding nature and stabilization of Al13(THF)n cluster are then demonstrated by rationalizing the interactions between superatomic and molecular orbitals of Al13 and THF, respectively

Multi-Center Redox-Active System: Amine–Amine Electronic Coupling through a Cyclometalated Bisruthenium Segment

A multicenter redox-active system with a linear N–Ru–Ru–N array, where two distal triarylamine sites are bridged by a cyclometalated bisruthenium segment, has been synthesized and characterized with single-crystal X-ray analysis. This system displays four consecutive and separate anodic redox waves at low potentials, indicating the presence of amine–amine electronic coupling with a distance of 19.16 Å through the cyclometalated bisruthenium segment. In contrast, when a noncyclometalated bisruthenium bridge is used, no amine–amine coupling is present. Upon stepwise oxidation by chemical or electrochemical methods, four-step absorption spectral changes occur in the visible to near-infrared region. In addition, the EPR studies and DFT and TDDFT calculations of the singly oxidized state are presented

Electronic Communication between Two Amine Redox Centers Bridged by a Bis(terpyridine)ruthenium(II) Complex

Two bis(terpyridine)ruthenium(II) complexes 2 and 3 appended with one or two di-p-anisylamino groups, respectively, were synthesized and fully characterized. Their electronic properties were studied by electrochemical and spectroscopic analyses. Electronic communication between individual amine sites of 3 was estimated by intervalence charge-transfer band analyses

Modulating PCBM-Acceptor Crystallinity and Organic Solar Cell Performance by Judiciously Designing Small-Molecule Mainchain End-Capping Units

In this article, we report that the bulk-size and electron-donating/electron-accepting nature of moieties, which are end-capping onto small-molecule donor mainchain, not only modulate the donor’s absorption, molecular frontier orbitals, and phase ordering, but also effectively tune the PC₇₁BM-acceptor phase crystallinity. Compared to the electron-deficient trifluoromethyl (SM-CF₃) units on the diketopyrrolopyrrole (DPP) small molecule mainchain ends, the electron-rich methoxyl (SM-OCH₃) units ending on the same mainchain help improve the PC₇₁BM-acceptor phase short-range ordering. As a result, the −OCH₃ capping small-molecule displays larger short-circuit current density (<i>J</i>_sc) when blended with PC₇₁BM (10.72 ± 0.22 vs. 16.15 ± 0.53 mA/cm²). However, the electron-donating nature of −OCH₃ raises the donor HOMO level, which leads to a quite small open-circuit voltage (<i>V</i>_oc) (0.624 vs. 0.881 V). Replacement of the −OCH₃ with the large and weak electron-donating aromatic carbazolyl (SM-Cz) ones affords the small molecule of SM-Cz. The SM-Cz:PC₇₁BM system affords a high <i>V</i>_oc of 0.846 V and a large <i>J</i>_sc of 13.33 ± 0.34 mA/cm² after thermal annealing, and hence gives a larger power conversion efficiency (PCE) of 6.26 ± 0.13%, which is among the top values achieved so far from the DPP molecules. Taken together, these results demonstrate that engineering the end-capping units on small-molecule donor mainchain can effectively modulate the organic solar cell performance

Electronic Communication between Two Amine Redox Centers Bridged by a Bis(terpyridine)ruthenium(II) Complex

Two bis(terpyridine)ruthenium(II) complexes 2 and 3 appended with one or two di-p-anisylamino groups, respectively, were synthesized and fully characterized. Their electronic properties were studied by electrochemical and spectroscopic analyses. Electronic communication between individual amine sites of 3 was estimated by intervalence charge-transfer band analyses

Synthesis of Vinyl-Substituted Polypyridyl Ligands through Suzuki–Miyaura Cross-Coupling of Potassium Vinyltrifluoroborate with Bromopolypyridines

Suzuki–Miyauru cross-coupling of bromopolypyridines with potassium vinyltrifluoroborate affords vinyl-substituted polypyridyl ligands in moderate to good yields. This reaction allows simple and practical syntheses of numerous vinyl-substituted polypyridines, such as 4′-vinyl-2,2′:6′,2′′-terpyridine, 5,5′-divinyl-2,2′-bipyridine, and 4,4′-divinyl-2,2′-bipyridine. In addition, a new ruthenium complex, [Ru(5,5′-divinyl-2,2′-bipyridine)3]2+, was synthesized and found to undergo reductive electropolymerization smoothly

Five-Stage Near-Infrared Electrochromism in Electropolymerized Films Composed of Alternating Cyclometalated Bisruthenium and Bis-triarylamine Segments

Oxidative electropolymerization of cyclometalated bisruthenium complexes [(Nptpy)2Ru2(tppyr)]­(PF6)2 and [(Nptpy)2Ru2(tpb)]­(PF6)2 produced adherent metallopolymeric films on electrode surfaces, where Nptpy is 4′-(p-N,N-diphenylamino)­phenyl-2,2′:6′,2″-terpyridine, tppyr is the 2,7-bisdeprotonated form of 1,3,6,8-tetra­(pyrid-2-yl)­pyrene, and tpb is the 3,6-bisdeprotonated form of 1,2,4,5-tetra­(pyrid-2-yl)­benzene. The resulting polymers are composed of two types of alternating constituent units: tppyr- or tpb-bridged cyclometalated bisruthenium units and biphenyl-bridged bis-triarylamine segments. These films exhibited four well-defined anodic redox couples as a result of the stepwise oxidations of these two units. By manipulating the intervalence charge-transfer transitions of mixed-valent bisruthenium and bis-triarylamine units, five-stage near-infrared electrochromism with stepwise color changes accompanied by good contrast ratio and coloration efficiency has been realized in these films. The film characterization by scanning electronic microscopy and X-ray photoelectron spectroscopy techniques are presented as well

Metallopolymeric Films Based on a Biscyclometalated Ruthenium Complex Bridged by 1,3,6,8-Tetra(2-pyridyl)pyrene: Applications in Near-Infrared Electrochromic Windows

A biscyclometalated ruthenium complex bridged by the 2,7-deprotonated form of 1,3,6,8-tetra­(2-pyridyl)­pyrene was deposited onto indium–tin oxide glass electrodes by reductive electropolymerization. The resulting metallopolymeric films exhibited tricolor electrochromic behavior in the near-infrared region upon switching of the two well-separated RuII/III processes at low potentials. A good contrast ratio (35%) at 2050 nm and a long memory time up to 100 min were recorded for this electrochromic behavior. The response time is typically of a few seconds