6 research outputs found
A Coarse-Grained Model for Free and Template-Bound Porphyrin Nanorings
Coarse-grained
simulation models are developed to study both template-bound
and free porphyrin nanoring systems. Key interactions are modeled
with relatively simple (and physically motivated) energy functions
which allow for relatively facile transfer both between different
ring sizes and between the template-bound and free nanoring systems.
The effects of varying the model parameters on the respective radii
of gyration are determined. The effects of including different templates
on the ring structure are investigated both in terms of the detailed
geometry of the template and the interaction strength between the
template and the metal centers in the nanorings. The role of the template-nanoring
interaction strength in controlling potential “caterpillar
track” rotational motion is discussed. The relationship of
the model to experimental small-angle X-ray, exchange spectroscopy,
and electron spin resonance results is discussed
Synthesis of Polyyne Rotaxanes
Active-metal templating has been used to synthesize rotaxanes consisting of a phenanthroline-based macrocycle threaded around a C8, C12, or C20 polyyne chain. The crystal structure of the C12 rotaxane has been determined. In the rhenium(I) carbonyl complex of this rotaxane, with Re(CO)<sub>3</sub>Cl coordinated to the phenanthroline macrocycle, the proximity of the polyyne chain quenches the luminescence of the rhenium. These rotaxanes offer a new approach to controlling the environment and interactions of a polyyne chain
Synthesis of Polyyne Rotaxanes
Active-metal templating has been used to synthesize rotaxanes consisting of a phenanthroline-based macrocycle threaded around a C8, C12, or C20 polyyne chain. The crystal structure of the C12 rotaxane has been determined. In the rhenium(I) carbonyl complex of this rotaxane, with Re(CO)<sub>3</sub>Cl coordinated to the phenanthroline macrocycle, the proximity of the polyyne chain quenches the luminescence of the rhenium. These rotaxanes offer a new approach to controlling the environment and interactions of a polyyne chain
Mechanical Stiffening of Porphyrin Nanorings through Supramolecular Columnar Stacking
Solvent-induced aggregates of nanoring
cyclic polymers may be transferred
by electrospray deposition to a surface where they adsorb as three-dimensional
columnar stacks. The observed stack height varies from single rings
to four stacked rings with a layer spacing of 0.32 ± 0.04 nm
as measured using scanning tunneling microscopy. The flexibility of
the nanorings results in distortions from a circular shape, and we
show, through a comparison with Monte Carlo simulations, that the
bending stiffness increases linearly with the stack height. Our results
show that noncovalent interactions may be used to control the shape
and mechanical properties of artificial macromolecular aggregates
offering a new route to solvent-induced control of two-dimensional
supramolecular organization
Optimizing the Energy Offset between Dye and Hole-Transporting Material in Solid-State Dye-Sensitized Solar Cells
The
power-conversion efficiency of solid-state dye-sensitized solar
cells can be optimized by reducing the energy offset between the highest
occupied molecular orbital (HOMO) levels of dye and hole-transporting
material (HTM) to minimize the loss-in-potential. Here, we report
a study of three novel HTMs with HOMO levels slightly above and below
the one of the commonly used HTM 2,2′,7,7′- tetrakis(<i>N</i>,<i>N</i>-di-<i>p</i>-methoxyphenylamino)-9,9′-spirobifluorene
(spiro-OMeTAD) to systematically explore this possibility. Using transient
absorption spectroscopy and employing the ruthenium based dye Z907
as sensitizer, it is shown that, despite one new HTM showing a 100%
hole-transfer yield, all devices based on the new HTMs performed worse
than those incorporating spiro-OMeTAD. We further demonstrate that
the design of the HTM has an additional impact on the electronic density
of states present at the TiO<sub>2</sub> electrode surface and hence
influences not only hole- but also electron-transfer from the sensitizer.
These results provide insight into the complex influence of the HTM
on charge transfer and provide guidance for the molecular design of
new materials
Slide tracheoplasty for congenital funnel-shaped tracheal stenosis.
Congenital funnel-shaped trachea is a serious condition, and the survival rate in infants is poor. A slide tracheoplasty is described, with a brief review of other methods of repair. Two cases that demonstrate the operability of congenital funnel-shaped trachea in infancy are reported