skip to main content

Title: Synergistic regulation of nonbinary molecular switches by protonation and light

We report a molecular switching ensemble whose states may be regulated in synergistic fashion by both protonation and photoirradiation. This allows hierarchical control in both a kinetic and thermodynamic sense. These pseudorotaxane-based molecular devices exploit the so-called Texas-sized molecular box (cyclo[2]-(2,6-di(1H-imidazol-1-yl)pyridine)[2](1,4-dimethylenebenzene); 14+, studied as its tetrakis-PF6salt) as the wheel component. Anions of azobenzene-4,4′-dicarboxylic acid (2H+•2) or 4,4′-stilbenedicarboxylic acid (2H+•3) serve as the threading rod elements. The various forms of 2 and 3 (neutral, monoprotonated, and diprotonated) interact differently with 14+, as do the photoinducedcisortransforms of these classic photoactive guests. The net result is a multimodal molecular switch that can be regulated in synergistic fashion through protonation/deprotonation and photoirradiation. The degree of guest protonation is the dominating control factor, with light acting as a secondary regulatory stimulus. The present dual input strategy provides a complement to more traditional orthogonal stimulus-based approaches to molecular switching and allows for the creation of nonbinary stimulus-responsive functional materials.

; ; ; ; ;
Publication Date:
Journal Name:
Proceedings of the National Academy of Sciences
Page Range or eLocation-ID:
Article No. e2112973118
Proceedings of the National Academy of Sciences
Sponsoring Org:
National Science Foundation
More Like this
  1. Five new divalent metal coordination polymers containing either 1,3‐adamantanedicarboxylate (adc) or 1,3‐adamantanediacetate (ada) and pillaring dipyridyl ligands were prepared and structurally characterized by single‐crystal X‐ray diffraction. Using the V‐shaped linker 4,4′‐dipyridylamine (dpa), three new phases were isolated. {[Zn2(ada)2(dpa)2]·4.5H2O}n(1) shows a (4,4) grid topology with embedded octameric water clusters. {[Co(ada)(dpa)(H2O)]·H2O}n(2) also manifests a 2D dimensionality, but with an intriguing novel (4)(12)(4.125) looped topology. {[Cd(adc)(H2O)2]·H2O}n(3) did not incorporate dpa ligands during self‐assembly, but exhibits an uncommon 3‐connected 83etbnetwork topology. [Co(ada)(ebin)]n(4) [ebin = ethanediaminebis(nicotinamide)] possesses a (3,6) triangular net based on {Co2(OCO)2} dimeric units. {[Cd(adc)(ebin)]·2H2O}n(5) also shows dimeric units, although linked into a decorated (4,4) grid topology. Magnetic susceptibility studies of compound4revealed a decrease inχmTproduct upon cooling, ascribed to antiferromagnetic coupling concomitant with single‐ion effects [g= 2.39(2) withD= 40(3) cm–1andJ= –3.55(4) cm–1]. Compounds1and5undergo blue‐violet fluorescence upon ultraviolet irradiation; the zinc derivative1shows potential as a sensor for the solution‐phase detection of nitrobenzene andm‐nitrophenol. Thermal decomposition behavior of the five new phases is also discussed.

  2. Abstract

    Nitrous acid (HONO) plays pivotal roles in various metal‐free as well as metal‐mediated routes relevant to biogeochemistry, atmospheric chemistry, and mammalian physiology. While the metastable nature of HONO hinders the detailed investigations into its reactivity at a transition metal site, this report herein utilizes a heteroditopic copper(II) cryptate [oC]CuIIfeaturing a proton‐responsive second‐coordination‐sphere located at a suitable distance from a [CuII](ONO) core, thereby enabling isolation of a [CuII](κ1‐ONO⋅⋅⋅H+) complex (2HNO2). A set of complementary analytical studies (UV‐vis,14N/15N FTIR,15N NMR, HRMS, EPR, and CHN) on2H‐NO2and its15N‐isotopomer (2H‐15NO2) reveals the formulation of2H‐NO2as {[oCH]CuII(κ1‐ONO)}(ClO4)2. Non‐covalent interaction index (NCI) based on reduced density gradient (RDG) analysis on {[oCH]CuII(κ1‐ONO)}2+discloses a H‐bonding interaction between the apical 3° ammonium site and the nitrite anion bound to the copper(II) site. The FTIR spectra of [CuII](κ1‐ONO⋅⋅⋅H+) species (2H‐NO2) shows a shift of ammonium NH vibrational feature to a lower wavenumber due to the H‐bonding interaction with nitrite. The reactivity profile of [CuII](κ1‐ONO⋅⋅⋅H+) species (2H‐NO2) towards anaerobic nitration of substituted phenol (2,4‐DTBP) is distinctly different relative to that of the closely related tripodal [CuII]‐nitrite complexes (1‐NO2/3‐NO2/4‐NO2).


    We report new ruthenium complexes bearing the lipophilic bathophenanthroline (BPhen) ligand and dihydroxybipyridine (dhbp) ligands which differ in the placement of the OH groups ([(BPhen)2Ru(n,n′‐dhbp)]Cl2withn = 6 and 4 in 1Aand 2A, respectively). Full characterization data are reported for 1Aand 2Aand single crystal X‐ray diffraction for 1A. Both 1Aand 2Aare diprotic acids. We have studied 1A, 1B, 2A, and 2B(B = deprotonated forms) by UV‐vis spectroscopy and 1 photodissociates, but 2 is light stable. Luminescence studies reveal that the basic forms have lower energy3MLCT states relative to the acidic forms. Complexes 1Aand 2Aproduce singlet oxygen with quantum yields of 0.05 and 0.68, respectively, in acetonitrile. Complexes 1 and 2 are both photocytotoxic toward breast cancer cells, with complex 2 showing EC50light values as low as 0.50 μM with PI values as high as >200vs. MCF7. Computational studies were used to predict the energies of the3MLCT and3MC states. An inaccessible3MC state for 2Bsuggests a rationale for why photodissociation does not occur with the 4,4′‐dhbp ligand. Low dark toxicity combined with an accessible3MLCT state for1O2generation explains the excellent photocytotoxicity of 2.

  4. Summary

    Chemotrophic microorganisms gain energy for cellular functions by catalyzing oxidation–reduction (redox) reactions that are out of equilibrium. Calculations of the Gibbs energy (ΔGr) can identify whether a reaction is thermodynamically favourable and quantify the accompanying energy yield at the temperature, pressure and chemical composition in the system of interest. Based on carefully calculated values ofΔGr, we predict a novel microbial metabolism – sulfur comproportionation (3H2S ++ 2H+4S0+ 4H2O). We show that at elevated concentrations of sulfide and sulfate in acidic environments over a broad temperature range, this putative metabolism can be exergonic (ΔGr<0), yielding ~30–50 kJ mol−1. We suggest that this may be sufficient energy to support a chemolithotrophic metabolism currently missing from the literature. Other versions of this metabolism, comproportionation to thiosulfate (H2S ++ H2O) and to sulfite (H2S + 34+ 2H+), are only moderately exergonic or endergonic even at ideal geochemical conditions. Natural and impacted environments, including sulfidic karst systems, shallow‐sea hydrothermal vents, sites of acid mine drainage, and acid–sulfate crater lakes, may be ideal hunting grounds for finding microbial sulfur comproportionators.

  5. Abstract

    Tailoring the doping of semiconductors in heterojunction solar cells shows tremendous success in enhancing the performance of many types of inorganic solar cells, while it is found challenging in perovskite solar cells because of the difficulty in doping perovskites in a controllable way. Here, a small molecule of 4,4′,4″,4″′‐(pyrazine‐2,3,5,6‐tetrayl) tetrakis (N,N‐bis(4‐methoxyphenyl) aniline) (PT‐TPA) which can effectively p‐dope the surface of FAxMA1−xPbI3(FA: HC(NH2)2; MA: CH3NH3) perovskite films is reported. The intermolecular charge transfer property of PT‐TPA forms a stabilized resonance structure to accept electrons from perovskites. The doping effect increases perovskite dark conductivity and carrier concentration by up to 4737 times. Computation shows that electrons in the first two layers of octahedral cages in perovskites are transferred to PT‐TPA. After applying PT‐TPA into perovskite solar cells, the doping‐induced band bending in perovskite effectively facilitates hole extraction to hole transport layer and expels electrons toward cathode side, which reduces the charge recombination there. The optimized devices demonstrate an increased photovoltage from 1.12 to 1.17 V and an efficiency of 23.4% from photocurrent scanning with a stabilized efficiency of 22.9%. The findings demonstrate that molecular doping is an effective route to control the interfacial charge recombination in perovskite solar cells which ismore »in complimentary to broadly applied defect passivation techniques.

    « less