Tunable Symmetry-Breaking-Induced Dual Functions in Stable and Photoswitched Single-Molecule Junctions.

The aim of molecular electronics is to miniaturize active electronic devices and ultimately construct single-molecule nanocircuits using molecules with diverse structures featuring various functions, which is extremely challenging. Here, we realize a gate-controlled rectifying function (the on/off ratio reaches ∼60) and a high-performance field effect (maximum on/off ratio >100) simultaneously in an initially symmetric single-molecule photoswitch comprising a dinuclear ruthenium-diarylethene (Ru-DAE) complex sandwiched covalently between graphene electrodes. Both experimental and theoretical results consistently demonstrate that the initially degenerated frontier molecular orbitals localized at each Ru fragment in the open-ring Ru-DAE molecule can be tuned separately and shift asymmetrically under gate electric fields. This symmetric orbital shifting (AOS) lifts the degeneracy and breaks the molecular symmetry, which is not only essential to achieve a diode-like behavior with tunable rectification ratio and controlled polarity, but also enhances the field-effect on/off ratio at the rectification direction. In addition, this gate-controlled symmetry-breaking effect can be switched on/off by isomerizing the DAE unit between its open-ring and closed-ring forms with light stimulus. This new scheme offers a general and efficient strategy to build high-performance multifunctional molecular nanocircuits.

Hysteresis Photomodulation via Single-Crystal-to-Single-Crystal Isomerization of a Photochromic Chain of Dysprosium Single-Molecule Magnets.

A one-dimensional coordination solid 1c is synthesized by reaction of a bispyridyl dithienylethene (DTE) photochromic unit with the highly anisotropic dysprosium-based single-molecule magnet [Dy(Tppy)F(pyridine)2]PF6. Slow magnetic relaxation characteristics are retained in the chain compound 1c, and photoisomerization of the bridging DTE ligand induces a single-crystal-to-single-crystal transformation that can be monitored using photocrystallography. Notably, the resulting chain compound 1o exhibits faster low-temperature relaxation than that of 1c, which is apparent in magnetic hysteresis data collected for both compounds as high as 4 K. Ab initio calculations suggest that this photomodulation of the magnetic relaxation behavior is due to crystal packing changes rather than changes to the crystal field splitting upon ligand isomerization.

Dual Light and Redox Control of NIR Luminescence with Complementary Photochromic and Organometallic Antennae.

With the help of a judicious association between dithienylethene (DTE) units, an ytterbium ion, and a ruthenium carbon-rich complex, we describe (i) the efficient (on/off) switching of pure NIR luminescence with a photochromic unit absorbing in the UV range and (ii) the association of electrochemical and photochemical control of this NIR emission in a single system with nondestructive readout.

Self-Assembled Monolayers of Redox-Active 4d-4f Heterobimetallic Complexes.

In this work, we report the preparation of functional interfaces incorporating heterobimetallic systems consisting in the association of an electroactive carbon-rich ruthenium organometallic unit and a luminescent lanthanide ion (Ln = Eu3+ and Yb3+). The organometallic systems are functionalized with a terminal hexylthiol group for subsequent gold surface modification. The formation of self-assembled monolayers (SAMs) with these complex molecular architectures are thoroughly demonstrated by employing a combination of different techniques, including infrared reflection absorption spectroscopy, ellipsometry, contact angle, and cyclic voltammetry measurements. The immobilized heterobimetallic systems show fast electron-transfer kinetics and, hence, are capable of fast electrochemical response. In addition, the characteristic electrochemical signals of the SAMs were found to be sensitive to the presence of lanthanide centers at the bipyridyl terminal units. A positive shift of the potential of the redox signal is readily observed for lanthanide complexes compared to the bare organometallic ligand. This effect is equally observed for preformed complexes and on-surface complexation. Thus, an efficient ligating recruitment of europium and ytterbium cations at gold-modified electrodes is demonstrated, allowing for an easy electrochemical detection of the lanthanide ions along with an alternative preparative method of SAMs incorporating lanthanide cations compared to the immobilization of the preformed complex.

Development of an Immuno-SPECT/Fluorescent Bimodal Tracer Targeting Human or Murine PD-L1 on Preclinical Models.

Detection of biomarkers to diagnose, treat, and predict the efficacy of cancer therapies is a major clinical challenge. Currently, biomarkers such as PD-L1 are commonly detected from biopsies, but this approach does not take into account the spatiotemporal heterogeneity of their expression in tumors. A solution consists in conjugating monoclonal antibodies (mAbs) targeting these biomarkers with multimodal imaging probes. In this study, a bimodal [111In]-DOTA-aza-BODIPY probe emitting in the near-infrared (NIR) was grafted onto mAbs targeting murine or human PD-L1 either in a site-specific or random manner. In vitro, these bimodal mAbs showed a good stability and affinity for PD-L1. In vivo, they targeted specifically PD-L1 and were detected by both fluorescence and SPECT imaging. A significant benefit of site-specific conjugation on glycans was observed compared to random conjugation on lysine. The potential of this bimodal agent was also highlighted, thanks to a proof of concept of fluorescence-guided surgery in a human PD-L1+ tumor model.

Electronic transport through single-molecule oligophenyl-diethynyl junctions with direct gold-carbon bonds formed at low temperature.

We report on the first systematic transport study of alkynyl-ended oligophenyl-diethynyl (OPA) single-molecule junctions with direct Au-C anchoring scheme at low temperature using the mechanically controlled break junction technique. Through quantitative statistical analysis of opening traces, conductance histograms and density functional theory studies, we identified different types of junctions, classified by their conductance and stretching behavior, for OPA molecules between Au electrodes with two to four phenyl rings. We performed inelastic electron tunneling spectroscopy and observed the excitation of Au-C vibrational modes confirming the existence of Au-C bonds at low temperature and compared the stability of molecule junctions upon mechanical stretching. Our findings reveal the huge potential for future functional molecule transport studies at low temperature using alkynyl endgroups.