We integrated single wall carbon nanotubes (SWNT), several water-soluble pyrene derivatives, which either bear negatively (pyrene-) or positively charged (pyrene+) charged ionic headgroups, and a series of water-soluble metalloporphyrins (MP8+/MP8-) into functional nanohybrids through a combination of associative van-der-Waals and electrostatic interactions. The resulting SWNT / pyrene and SWNT / pyrene / MP were characterized by spectroscopic and microscopic means and were found to form stable nanohybrid structures in aqueous media. When the nanohybrid systems are photoexcited with visible light, a rapid intrahybrid charge separation causes the reduction of the electron accepting SWNT and, simultaneously, the oxidation of the electron donating MP. Beneficial are charge recombination dynamics that are located in the Marcus-inverted region.
The mass-strength ratio is of exceptional importance for space application. The critical parts of both shuttle vehicles and satellites depends on strength and toughness of the materials they are made of, while strict limitations on the weight of the different components are placed by the launch technology. Single wall carbon nanotubes (SWNT) present significant potential as the basic material for the space applications. Exceptional mechanical properties of single wall carbon nanotubes (SWNT) have prompted intensive studies of SWNT composites. These qualities can also be used in a variety of other technologies from automotive to military and medical. However, the present composites have shown only a moderate strength enhancement when compared to other hybrid materials. Although substantial advances have been made, mechanical characteristics of SWNT-doped polymers are noticeably below their highly anticipated potential. Pristine SWNTs are well known for poor solubilization, which leads to phase segregation of composites. Severe structural inhomogeneities result in the premature failure of the hybrid SWNT/polymer materials. The connectivity with and uniform distribution within the matrix are essential structural requirements for the strong SWNT composites. Here we show that a new processing approach based on sequential layering of chemically-modified nanotubes and polyelectrolytes can greatly diminish the phase segregation and render SWNT composite highly homogeneous. Combined with chemical cross-linking, this processing leads to drastically improved mechanical properties. Tensile strength of the composites is several times higher than that of SWNT composites made via mixing; it approaches values seen for hard ceramics. The universality of the layering approach applicable to a wide range of functional materials makes possible successful incorporation of SWNT into a variety of composites imparting them required mechanical properties. The thin film membranes that are obtained in the result of the layer-by-layer process can be used as an intermediate or as a component of ultrastrong laminates. At the same time, the prepared membranes can also be utilized in the as-prepared form for the large area space telescopes (both radio and optical) because the combine the strength and multiple functionality of the SWNT membranes with the ease of deployment.
Excited states properties of supramolecular fullerene donor- bridge-acceptor dyads were studied under various conditions. The steady-state emission yields of C60-Fc and Ru-C60 dyads are noticeably quenched relative to ruthenium and fullerene model compounds, respectively. This indicates that intramolecular electron-energy transfer plays a predominant contribution in the deactivation of the photoexcited chromophores, e.g. the singlet excited state of the fullerene core and ruthenium excited MLCT state. Picosecond and nanosecond resolved photolysis show that the photoexcited C60-Fc and Ru-C60 dyads transform rapidly into charge separated states. Characteristic NIR absorption of the fullerene (pi) -radical anions were complimented by a detailed UV/vis analysis and confirm the existence of long-lived radical pairs. The structure, length, and nature of the bridging spacer separating the two reactive centers had a significant impact on the lifetime nd stabilization of the charge separated states.
Time-resolved and steady-state techniques are employed to explore the photophysical properties of C60C(COOEt)2, equatorial-C60[C(COOEt)2]2, trans3- C60[C(COOEt)2]2, trans2-C60[C(COOEt)2]2, and equatorial-C60[C(COOEt)2]3. Picosecond-resolved energy transfer to the fullerene core results in the formation of the excited singlet state with remarkably blue-shifted singlet-singlet transitions in going from C60 to 3. Rapid formation of the triplet-triplet absorption as a consequence of intersystem crossing to the energetically lower lying excited triplet state suffers a deceleration with increasing number of functionalizing addends. The corresponding triplet-triplet absorption energies also show a significant dependence on the degree and site of functionalization, spreading over a range of 100 nm. Energy transfer from radiolytically excited biphenyl to the fullerene's ground state, corroborates the photolytic data. 0->0 transitions from the lowest level of the excited singlet state and excited triplet state are mirror- images to the reversed 0->0 absorption transitions. Red- shifts of these emission, relative to pristine C60, again sensitively reflect the degree and site of functionalization. Cyclic voltammetry and reductive quenching of triplet excited fullerenes demonstrate that functionalization of the fullerene's (pi) -system obstructs the ease of reduction in the ground and excited triplet state. An increasing number of bis(ethoxycarbonyl)methylene groups shifts the redox potential of the ground state from -0.54 to -0.86 V versus SCE and of the excited triplet state from +1.01 V versus SCE to +0.64 V versus SCE for C60 and 3, respectively.