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Alberto Credi

Publications and source records attributed to Alberto Credi.

7 recordsLinked to original sources
PubMed2003

Molecular logic circuits.

Miniaturization has been an essential ingredient in the outstanding progress of information technology over the past fifty years. The next, perhaps ultimate, limit of miniaturization is that of molecules, which are the smallest entities with definite size, shape, and properties. Recently, great effort has been devoted to design and investigate molecular-level systems that are capable of transferring, processing, and storing information in binary form. Some of these nanoscale devices can, in fact, perform logic operations of remarkable complexity. This research--although far from being transferred into technology--is attracting interest, as the nanometer realm seems to be out of reach for the "top-down" techniques currently available to microelectronics industry. Moreover, such studies introduce new concepts in the "old" field of chemistry and stimulate the ingenuity of researchers engaged in the "bottom-up" approach to nanotechnology.

Journal Article↗
PubMed2002

The bottom-up approach to molecular-level devices and machines.

The macroscopic concepts of a device and a machine can be extended to the molecular level. Molecular-level devices and machines are constructed by a bottom-up approach. The atom-by-atom bottom-up approach is unrealistic from the chemical viewpoint. The bottom-up approach molecule-by-molecule following the guidelines of supramolecular (multicomponent) chemistry has proved to be successful. The extension of the concepts of a device and a machine to the molecular level is of interest not only for basic research, but also for the growth of nanoscience and the development of nanotechnology.

Journal Article↗
PubMed2002

Photoinduced electron transfer in a triad that can be assembled/disassembled by two different external inputs. Toward molecular-level electrical extension cables.

We have designed, synthesized, and investigated a self-assembling supramolecular system which mimics, at a molecular level, the function performed by a macroscopic electrical extension cable. The system is made up of three components, 12+, 2-H3+, and 3. Component 12+ consists of two moieties: a [Ru(bpy)3]2+ unit, which plays the role of an electron donor under light excitation, and a DB24C8 crown ether, which fulfills the function of a socket. The wire-type component 2-H3+ is also composed of two moieties, a secondary dialkylammonium-ion center and a bipyridinium unit, which thread into the DB24C8 crown-ether socket of 12+ and the 1/5DN38C10 crown-ether socket 3, respectively. The photochemical, photophysical, and electrochemical properties of the three separated components, of the 12+ superset 2-H3+ and 2-H3+ subset 3 dyads, and of the 12+ superset 2-H3+ subset 3 triad have been investigated in CH2Cl2 solution containing 2% MeCN. Reversible connection/disconnection of the two plug/socket systems can be controlled independently by acid/base and redox stimulation. The behavior of the various different dyads and triad has been monitored by light absorption and emission spectroscopies, as well as by electrochemical techniques. In the fully connected 12+ superset 2-H3+ subset 3 triad, light excitation of the [Ru(bpy)3]2+ unit of component 12+ is followed by electron transfer (k = 2.8 x 108 s-1) to the bipyridinium unit of component 2-H3+, which is plugged into component 3. Possible schemes to obtain improved molecular-level electrical extension cables are discussed.

Journal Article↗
PubMed2002

Ferrocene-containing carbohydrate dendrimers.

Aliphatic amines, incorporating one or three (branched) acylated beta-D-glucopyranosyl residues, were coupled with the acid chloride of ferrocenecarboxylic acid and with the diacid chloride of 1,1'-ferrocenedicarboxylic acid to afford four dendrimer-type, carbohydrate-coated ferrocene derivatives in good yields (54-92%). Deprotection of the peracylated beta-D-glucopyranosyl residues was achieved quantitatively by using Zemplén conditions, affording four water-soluble ferrocene derivatives. When only one of the two cyclopentadienyl rings of the ferrocene unit is substituted, strong complexes are formed with beta-cyclodextrin in H2O, as demonstrated by liquid secondary ion mass spectrometry (LSIMS), 1H NMR spectroscopy, electrochemical measurements, and circular dichroism spectroscopy. Molecular dynamics calculations showed that the unsubstituted cyclopentadienyl ring is inserted through the cavity of the toroidal host in these complexes. The electrochemical behavior of the protected and deprotected ferrocene-containing dendrimers was investigated in acetonitrile and water, respectively. The diffusion coefficient decreases with increasing molecular weight of the compound. The potential for oxidation of the ferrocene core, the rate constant of heterogeneous electron transfer, and the rate constant for the energy-transfer reaction with the luminescent excited state of the [Ru(bpy)3]2+ complex (bpy = 2,2'-bipyridine) are strongly affected by the number (one or two) of substituents and by the number (one or three) of carbohydrate branches present in the substituents. These effects are assigned to shielding of the ferrocene core by the dendritic branches. Electrochemical evidence for the existence of different conformers for one of the dendrimers in aqueous solution was obtained.

Carbohydrates↗
PubMed1998

Diastereoselective Formation and Photophysical Behavior of a Chiral Copper(I) Phenanthroline Complex.

The Friedländer condensation of (1R,5S)-(+)- and (1S,5R)-(-)-nopinone with 8-aminoquinoline-7-carbaldehyde leads to the corresponding enantiomerically pure (2,3-b)-pineno-1,10-phenanthrolines. Coordination of these ligands with Cu(I) affords non-interconvertable chiral complexes which show equal and opposite Cotton effects in their CD spectra as well as identical half-wave oxidation potentials of +0.37 V and identical MLCT absorptions at 442 nm. Both complexes are nonemissive at 298 and 77 K. Stern-Volmer quenching studies were carried out with optically pure Delta- and Lambda-[Ru(bpy)(3)](2+) and racemic [Ru(dpb)(3)](2+) as donors (bpy = 2,2'-bipyridine and dpb = 4,4'-diphenyl-bpy). Neither study provides any evidence of enantioselective quenching, indicating that energy or electron transfer may be occurring through a distance where chiral recognition is unimportant.

Journal Article↗
PubMed1997

Luminescent and Redox-Active Iridium(III)-Cyclometalated Compounds with Terdentate Ligands.

Two novel bis-terdentate Ir(III)-cyclometalated complexes, [Ir(L1)(L1(-))](2+) (1) and [Ir(L1(-))(2)](+) (2), have been prepared (L1 is 2,6-bis(7'-methyl-4'-phenyl-2'-quinolyl)pyridine; L1(-) is its mono-anion, see Figure 1). To the best of our knowledge, 1 and 2 are the first luminescent and redox-active Ir(III)-cyclometalated bis-terdentate compounds. In acetonitrile solution, on oxidation, 2undergoes a reversible, metal-centered, one-electron oxidation at +1.40 V, whereas 1 does not exhibit any oxidation process up to +2.00 V. On reduction, both compounds undergo four reversible ligand-centered one-electron processes. The absorption spectra of the compounds are dominated by moderately intense (epsilon in the 10(3)-10(4) M(-)(1) cm(-)(1) range) spin-allowed metal-to-ligand charge-transfer (MLCT) bands at wavelengths longer than 350 nm and by intense (epsilon in the 10(4)-10(5) M(-)(1) cm(-)(1) range) ligand-centered (LC) bands at shorter wavelengths. The complexes exhibit an intense luminescence both at 77 K in MeOH/EtOH, 4:1 (v/v), rigid matrix (1, lambda(max) = 592 nm, tau = 20 &mgr;s; 2, lambda(max) = 598 nm, tau = 9 &mgr;s) and at room temperature in deoxygenated acetonitrile solution (1, lambda(max) = 620 nm, tau = 325 ns, Phi = 0.005; 2, lambda(max) = 630 nm, tau = 2.3 &mgr;s, Phi = 0.066). In all cases, the emission is assigned to triplet MLCT levels (namely, Ir --> L1 and Ir --> L1(-) in 1 and 2, respectively).

Journal Article↗