Maria Teresa Gandolfi

Photoinduced electron flow in a self-assembling supramolecular extension cable

We report the design, bottom-up construction, characterization, and operation of a supramolecular system capable of mimicking the function played by a macroscopic electrical extension cable. The system is made up of a light-powered electron source, an electron drain, and a cable as the molecular components programmed to self-assemble by means of two distinct plug/socket junctions. Such connections are reversible and can be operated independently by orthogonal chemical inputs. In the source–connector–drain supermolecule, photoinduced electron transfer from source to drain occurs, and it can be switched off by dual-mode chemically controlled disassembling of the molecular components.

Macrocycles, pseudorotaxanes and catenanes containing a pyrrolo-tetrathiafulvalene unit: absorption spectra, luminescence properties and redox behavior

The photophysical properties of (i) three macrocycles (1–3) of different size, each one incorporating a bis(2,5-dimethylpyrrolo[3,4-d])tetrathiafulvalene (TTFP) and a 1,4-dimethoxybenzene (DMB) electron-donating unit, (ii) the six pseudorotaxanes obtained by threading 1–3 with the electron acceptors dimethyldiazapyrenium (DMDAP2+) and dibenzyldiazapyrenium (DBDAP2+) and (iii) the three catenanes obtained by interlocking 1–3 with the electron-accepting cyclophane cyclobis(paraquat-p-phenylene) (CBPQT4+) have been investigated. The monooxidized and dioxidized species obtained by oxidation with Fe(III) of the TTFP unit contained in the above compounds have also been studied. The redox-driven dethreading/rethreading process has been investigated in the case of the pseudorotaxane based on the macrocycle 2 and the DMDAP2+ dication. In the catenanes, oxidation of the TTFP unit causes strong spectral changes, but does not promote disruption of the interlocked structures.

The self assembly of controllable [2]catenanes

The dynamic and electrochemical properties of two new [2]catenanes, in which bisparaphenylene-34-crown-10 is encircled by a cyclophane incorporating either (i) one bipyridinium and one bis(pyridinium)ethylene unit or (ii) two bis(pyridinium)ethylene units, are investigated in solution.

From a molecular to a supramolecular photochemistry

Abstract Following a current trend of chemical research, photochemical investigations are moving from molecular to supramolecular species. Some of the results obtained by the authors with supramolecular species containing metal complexes are briefly reviewed, with particular emphasis on (i) cage-type complexes, (ii) host-guest systems, (iii) metal catenates, and (iv) oligonuclear metal complexes.

Artificial molecular-level machines with [Ru(bpy)3]2

A molecular-level machine is an assembly of a discrete number of molecular components (that is, a supramolecular structure) designed to perform mechanical-like movements (output) as a consequence of appropriate external stimuli (input). Like macroscopic machines, molecular-level machines are characterized by (i) the kind of energy input supplied to make them work, (ii) the kind of movement performed by their components, (iii) the way in which their operation can be controlled and monitored, (iv) the possibility to repeat the operation at will and establish a cyclic process, (v) the time scale needed to complete a cycle of operation, and (vi) the function performed. The most convenient way to supply energy to an artificial molecular-level machine is through a photochemical reaction. [Ru(bpy)3]2

A simple fluorescent chemosensor for alkaline-earth metal ions

Abstract In acetonitrile solutions, the deprotonated form of 1-pyrenebutyric acid ( 1 ) forms 1:2 (metal:ligand) complexes with Zn 2+ , Cu 2+ , Fe 2+ , Fe 3+ , and earth alkali metal ions. The complexation process leads two pyrene moieties in close contact, so that dimers are formed, causing strong changes in the absorption and fluorescence spectra. Taking advantage of these changes, very low concentrations of earth alkali metal ions can be detected, suggesting 1 as a good prototype of a new family of fluorescent sensors.

The Synthesis and Spectroscopic Properties of Macrocyclic Polyethers Containing Two Different Aromatic Moieties and Their [2]Catenanes Incorporating Cyclobis(paraquat-p-phenylene)

The absorption spectra and luminescence properties of six new [2]catenanes are reported. The new catenanes are formed as a result of a template reaction of cyclobis(paraquat-p-phenylene) with six new derivatives of bis-p-phenylene-34-crown-10 in which the p-phenylene rings have been replaced variously by p-xylyl units, 1,5-, 1,6-, 2,6-, and 2,7-naphtho units, and a naphthalene-2,6-dimethylyl ring system. Dynamic 1H NMR spectroscopy reveals that some of the [2]catenanes exhibit translational isomerism (right). Comparison with the properties of simple model compounds shows the presence of intra- and intermolecular electronic interactions between the component units of the crown ethers and the catenanes.

Molecular-Level Artificial Machines Based on Photoinduced Electron-Transfer Processes

The concept of macroscopic machine can be extended to the molecular level. A molecular-level machine can be defined as an assembly of a discrete number of molecular components (that is, a supramolecular structure) designed to perform mechanical-like movements (output) as a consequence of appropriate external stimulation (input). Molecular-level machines operate via nuclear rearrangements and, like macroscopic machines, are characterized by (i) the kind of energy input supplied to make them work, (ii) the manner in which their operation can be monitored, (iii) the possibility to repeat the operation at will, i.e., establishing a cyclic process, (iv) the time scale needed to complete a cycle of operations, and (v) the performed function. The extension of the concept of machine to the molecular level is of great interest not only for basic research, but also for the growth of nanoscience and the development of nanotechnology. In this chapter recent examples of molecular-level machines based on pseudorotaxanes, rotaxanes, and catenanes, and operating by means of photoinduced electron-transfer processes are presented.

The synthesis and spectroscopic properties of a [2]catenane incorporating an anthracene chromophoric unit

A modified bis-p-phenylene-34-crown-10 ring in which one of the 1,4-dioxybenzene units has been replaced by a 9,10-dioxyanthracene unit has been employed as a template for the formation of cyclobis(paraquat-p-phenylene). The [2]catenane which results has been shown by 1H NMR spectroscopy to exist in solution exclusively in the translationally isomeric form in which (a) only the 1,4-dioxybenzene ring occupies the central cavity of the tetracationic cyclophane and (b) the crown ether ring is prevented from circumrotating through the cyclophane by the large 9,10-dioxyanthracene unit. The absorption spectrum and luminescence properties of this new [2]catenane and of its crown ether component in its free state have been investigated and compared with those of 1,4-dimethoxybenzene and a model anthracene derivative, carrying methylated triethylene glycol chains on the 9 and 10 positions of the anthracene ring. While the absorption spectrum of the crown ether is the sum of the spectra of the two component chromophoric moieties, its emission spectrum shows only the fluorescence band of the 9,10-dioxyanthracene-type unit. The excitation spectrum shows that the disappearance of the 1,4-dioxybenzene type emission in the crown ether is due to a very efficient (kq ≥ 4 × 1010 s−1) energy-transfer process from the 1,4-dioxybenzene to the 9,10-dioxyanthracene type unit. The absorption spectrum of the [2]catenane is noticeably different from the sum of the spectra of its two cyclic components, particularly as far as the presence of a very broad charge-transfer (CT) band in the visible spectral region (λmax = 545 nm, ϵmax = 615 M−1 cm−1) is concerned.Comparison with the CT band of a model compound shows that the very broad CT band of the [2]catenane is in fact the result of two component bands originating from the interaction of the two different electron-donor units (1,4-dioxybenzene and 9,10-dioxyanthracene type) present in the crown ether with the electron-acceptor bipyridinium-type units of the cyclobis(paraquat-p-phenylene). The emission spectrum of the [2]catenane does not show any band because of the quenching action (rate constant kq ≥ 5 × 1010 s−1) of the low-energy non-luminescent charge-transfer levels on the higher energy, potentially luminescent levels of the crown ether.

Tetrathiafulvalene and its Derivatives as π-Electron Donating Units in Pseudorotaxanes, Rotaxanes, and Catenanes

The in terest f or t etrathiafulvalene (hereafter in dicated a s TTF) began a bout s eventy years ago, but before 1970 only a few articles appeared in the literature [1]. In 1970 Wudl and coworkers observed that TTF can be reversibly oxidized to monocationic radical and dication [3]; both the charged species are stable in solution for a long time, and the first and second oxidation potential values can be finely tuned by appropriate substituents [4]. Since 1970 the work dealing with TTF has increased enormously. A few years later Ferraris et al. [5] observed that TTF reacts in the solid state with 7,7’,8,8’-tetracyano-p-quinodimethane (a good π-electron accepting unit), forming a molecular solid, which for its high electrical conductivity and some similarity with metals was named the first organic metal. For its chemical and electrochemical properties TTF (and its derivatives) is today considered an important building block in many fields of scientific research, both in physics and chemistry [6].