AK Prof. Dr. H. Langhals


High Performance Fluorescent Dyes - Switches for Light

High-performance semiconductors are universally known, they are the heart of electronics and play an increasing rôle in electrical components. What, however are high-performance fluorescent dyes? - They are the optical counterpart to high performance semiconductors.

Dual state and information recording devices are dominated by electronics. The most prominent example for this is the highly developed computer technology. Attractive as such systems may be, their limitations soon become obvious if high speed processing and high integration are required; the 10000 MHz region of processing is hardly attainable for PCP semiconductor computers and an area larger than a football stadium is required for the conventional wiring diagram of a modern micro processor. Moreover, the electrical connections behave less and less like wires if their dimensions are further decreased. The subject electrosmog gives an impression of the future problems if one tries to attain higher densities of integration and higher processing rates. - A completely novel technology is therefore required.

Photonics ("technology of light") is an attractive alternative to electronics because one can principally attain 500 Terahertz (5·1014 cycles per second) without problems. The construction of devices becomes possible with faster processing rates half a million times faster compared to our fastest PCP semiconductor computers to date. Moreover, light beams can cross each other without interference. Thus, it is not necessary to make wiring "around the corner" and this is of obvious advantage for attaining a high density of integration.

This novel and attractive photonic technology requires devices for signal processing such as switches and storage. This means that structures are required for the uptake and processing of light, preferently on the molecular scale in order to attain a high density of integration. The absorbed light should not get lost. Therefore, special dyes are required for the intermediate storage of light energy. Fluorescent dyes fulfil such requirements because they can re-emit the absorbed light after an intermediate storage.

The fluorescence quantum yield F is a measure of the quality of such dyes and indicates the percentage of stored light which is re-emitted. High-quality fluorescent dyes such as S-13 reach 100% of this quality indicator.

The photostability (light-fastness) is a further important measure of quality. This corresponds to the number of switching cycles of electric devices such as relays. More than 100 million cycles of absorption and processing of light are required for high-performance fluorescent dyes - no photodegradation of the dye S-13 could be detected, however, a chemical degradation is possible and this may be induced by light.

The aptitude for the absorption of light is a third important measure of the quality of dyes and is represented by the absorptivity e . The majority of textile dyes exhibit absorptivities of about 30000, but there are examples with more than 100000. An absorptivity of 87000 is attained by the highly stable dye S-13.

In photonic development all components should be developed on the basis of light, in order to obtain a homogeneous technology; electronics, if required, should be only coupled by an interface. Such a homogeneous photonics technology requires besides storage and processing devices also detectors, frequency doublers and interfaces. The molecular basis for such components is now to be established by the development of highly phototstable fluorescent dyes and the study of their chromophores and the interaction of several chromophores. The spin-offs of this research and development are novel fluorescent standards, for example, for the calibration of fluorescence spectrometers, novel laser dyes, novel membrane detectors and novel dyes for the near infrared; the latter are of importance for medicine and the technology of semiconductors


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