Applications optical limiters

Phthalocyanine derivatives of indium(III) have attracted even more interest.Some indium phthalocyanine adducts show interesting nonlinear optical properties.For example, tert-butyl-substituted chloro(phthalocyaninato)indium(III) (t-Bu)4PcInCl (24) is one of the best substances for optical-limiting applications. " Optical limiters limit the intensity of transmitted light once the input intensity exceeds a threshold value. This ability is useful for the protection of sensitive objects, such as human eyes or light sensors from high-intensity light beams. 

Light filters for colorimeters, see Filters, optical Limiting cathode potential 509 see also Controlled potential electro-analysis Linear regression 145 Lion intoximeter 747 Liquid amalgams applications of, 412 apparatus for reductions, 413 general discussion, 412 reductions with, (T) 413 zinc amalgam, 413 Liquid ion exchangers structure, 204 uses, 204, 560... 

One promising application for C60 is as an optical limiter. Optical limiters are used to protect people and materials from damage by high light intensities usually associated with intense pulsed sources. Optical limiting is accom-... 

Although there have been great advances in covalent functionalization of fullerenes to obtain surface-modified fullerene derivatives or fullerene polymers, the application of these compounds in composites still remains unexplored, basically because of the low availability of these compounds [132]. However, until now, modified fullerene derivatives have been used to prepare composites with different polymers, including acrylic [133,134] or vinyl polymers [135], polystyrene [136], polyethylene [137], and polyimide [138,139], amongst others. These composite materials have found applications especially in the field of optoelectronics [140] in which the most important applications of the fullerene-polymer composites have been in the field of photovoltaic and optical-limiting materials [141]. The methods to covalently functionalize fullerenes and their application for composites or hybrid materials are very well established and they have set the foundations that later were applied to the covalent functionalization of other carbon nanostructures including CNTs and graphene. 

The covalent chemistry of fullerenes has developed very rapidly in the past decade in an effort to modify fuUerene properties for a number of applications such as photovoltaic cells, infrared detectors, optical limiting devices, chemical gas sensors, three-dimensional electroactive polymers, and molecular wires [8, 25, 26, 80-82]. Systematic studies of the redox properties of Cgo derivatives have played a crucial role in the characterization of their unique electronic properties, which lie at the center of these potential applications. Furthermore, electrochemical techniques have been used to synthesize and separate new fullerene derivatives and their isomers as well as to prepare fullerene containing thin films and polymers. In this section, to facilitate discussion of their redox properties, Cgo derivatives have been classified in three groups on the basis of the type of attachment of the addend to the fullerene. In group one, the addends are attached via single bonds to the Cgo surface as shown in Fig. 6(a) and are referred to as singly bonded functionalized derivatives. The group includes... 

The small HOMO-LUMO band gap and presence of other close-in-energy MOs results in fullerenes being easily polarized. They all give very intense Raman scattering lines and have relatively large x values useful for NLO applications (11). Indeed, C60 is one of the best materials known to date for optical limiting. 

There is an increasing number of areas where bioreactors are serious alternatives to conventional chemical reactors, particularly when their mild conditions and high selectivity can be exploited. In the pharmaceutical industry micro-organisms and enzymes can be used to produce specific stereo-isomers selectively, a very desirable ability since it can be that only the one isomer (possibly an optical isomer) may possess the required properties. In such applications the limitations of bioreactors are clearly outweighed by the advantages in their use. The fact that the products are formed in rather dilute aqueous solution and at relatively low rates may be of secondary importance and it may then be economically feasible to employ multiple separation stages in their purification. 

A limiting factor in electron microscopy is the quality of the electron beam. Aberrations introduced by the optics limit both spatial resolution and analytical capabilities. There is a need to correct for the spherical and chromatic aberrations introduced by the electron optics. This will result in improved coherence of the beam and improved imaging and diffraction. In particular, these advances will permit the analysis of amorphous samples. Smaller beam sizes can also be achieved, allowing for sub-Angstrom resolution chemical analysis of samples. Development of higher-quality electron beams and short pulses of electron beams would broaden and deepen the application of electron microscopy. 

The incorporation of pendant Pcs to a polymeric backbone via the grafting of a suitable Pc molecule to a preformed polymer containing appropriate functional groups has been accomplished by Chen and co-workers [163], These authors exploited the axial reactivity of some metalloPcs (namely, In(III)Pcs) to prepare an In(III)Pc-polystyrene copolymer. The most remarkable feature of this material is that cofacial association between the macrocycles is fully prevented. For some applications of the Pcs, such as optical limiting or photodynamic therapy (PDT), aggregation should be avoided because it produces the quenching of the excited-states. 

High quantum yield photochemical reactions of condensed-phase species may become useful for future optical applications such as molecular switches, optical limiters, and read-write data storage media. Toward these ends, much research has been conducted on novel nonlinear chemical-based materials such as conducting polymers and metal-organic species. Monitoring the early time-dependent processes of these photochemical reactions is key to understanding the fundamental mechanisms and rates that control the outcome of these reactions, and this could lead to improved speed and efficiencies of devices. 

In the next few years, there will be many exciting developments related to NEMS devices. In particular, replacing the current chemically driven molecular machines with those stimulated by optical or electrical pulses - dramatically extending the range of applications. With so many possible nanobuilding blocks at our disposal, the scope of devices and resultant applications is limited only by our imaginations -an exciting area of discovery awaits ... 

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