A convenient approach for the self-assembly of well-defined porphyrin nanowires in water, wherein the individual monomers do not aggregate via pi-pi interactions, is disclosed. These unidirectional and heteromeric assemblies are instead composed of robust beta-CD/adamantane host/guest interactions. A combination of surface microscopies and fluorescence energy transfer experiments were conducted on the nanowires demonstrating their stability and resistance to disassembly.
The ligand-to-metal charge transfer state (LMCT) of [(dmpe)3Re](2+) (dmpe = 1,2-bis(dimethylphosphino)ethane) has been demonstrated to be a potent oxidant (E(0)(Re(2+*)/Re(+)) = 2.61 V vs standard calomel electrode). This complex has been traditionally prepared by nontrivial routes in low yields, and very little has been achieved in optimizing the ground state and emission energy properties of the general class of complexes [(PP)3Re](2+) (PP = chelating diphosphine) through phosphine modification. Improved syntheses for Re(I) tris-homoleptic diphosphine complexes [(PP)3Re](+) (PP = 1,2-bis(dimethylphosphino)ethane (dmpe), 1,2-bis(diethylphosphino)ethane (depe), bis(dimethylphosphino)methane (dmpm), bis(diphenylphosphino)methane (dppm), Me2PCH2PPh2, 1,3-bis(dimethylphosphino)propane (dmpp), or 1,2-bis(dimethyl-phosphino)benzene (dmpb)) were achieved by single-pot reactions exploiting the reducing potential of the phosphines when reacted with Re(V) oxo-complexes in 1,2-dichlorobenzene at 160-180 °C. Single-electron chemical oxidation of [(PP)3Re](+) yields luminescent Re(II) analogues; appropriate use of Ph3C(+), Cp2Fe(+), or (4-BrC6H4)3N(+) B(C6F5)4(-) salts produced [(PP)3Re](2+) complexes in good yields. Crystallographic trends for the Re(+)/Re(2+) pairs show significantly lengthened Re(2+)-P bonds for [(PP)3Re](2+) relative to the corresponding [(PP)3Re](+) system. The redox and luminescence behavior of the complexes indicates the luminescence is from a ligand P(σ)-to-metal (Re(dπ)) charge transfer ((2)LMCT) state for all the complexes. Structured luminescence at 77 K is postulated to originate from relaxation of the (2)LMCT state into two spin-orbit coupled states: the ground state and a state ∼ 3000 cm(-1) above the ground state. The excited-state reduction potential (Re(II*/I)) for [(depe)3Re](2+) was determined from the free energy dependence of luminescence quenching rate constants. Yields for formation of charge separated ions were determined for three of the complexes with a variety of electron donors. Despite favorable electrostatics, no charge separated ions were observed for radical ion pairs for which the energy of back electron transfer exceeded 1.1 V.
Micromechanical silicon cantilever structures of typical dimensions 1 mm x 80 pm x 5 pm have been excited by absorption of pulsed light from diode laser at 790 nm or a LED at 830 nm respectively. The excitation motion of the cantilevers was measured by means of a fiber -optic Michelson interferometer as well as a reflective multimode fiber optic pick up. In addition to the optical signal the electrical signal of a thin film piezoresistive transducer localized at the base of the cantilever has been measured. The optimal fiber position with respect to the cantilever was determined experimentally. At this position a signal to noise ratio of about 6 could be realized for the detected signal at 5 kHz bandwidth for optical power levels of 56 pW. Using a 125 pm diameter optical fiber this corresponds to an optical power density of 4.6 mW /mm2 which is below the critical value of 5 mW /mm2 suggested for explosive environments.
The proposal of the subject for this discussion is in itself a remarkable thing and a symbol of the spirit of this meeting. A few years ago the proposal would have looked preposterous. Proteins were known as a mysterious sort of colloids, the molecules of which eluded our search. W hat is it then th a t has happened in these years ? W hy is the most distinguished scientific society of this country inviting a discussion on the protein molecule ?The brilliant work on inorganic colloids, especially on gold sols, by Zsigmondy and others had shown th a t the mass of the particles of these colloids changed continually with the conditions of their formation. The particles had no individuality from the quantum point of view-therefore they were not molecules although they obeyed the same laws of therm al motion as the molecules. Now the proteins behaved in many respects like inorganic colloids, were held back by membranes, diffused very slowly, etc., and one therefore concluded th a t the protein particles were not molecules. Another line of thought led to the same conclusion. In spite of all their efforts and the wonderful achievements in other fields the organic chemists were not able to synthesize molecules of a mass approaching-even in a modest way-th a t of the protein particle. Giant molecules, therefore, were supposed not to exist-only clusters of ordinary small molecules forming particles of undefined mass.To-day we have, I think, definite proof th a t this view is wrong. Investi gations along different lines have given the result th a t the proteins are built up of particles possessing the hall-mark of individuality and therefore are in reality giant molecules. We have reason to believe th a t the particles in[ 40 ]
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