School of Mathematics and Natural Sciences

Molecular logic with color absorbing and emitting molecules based on spiropyran

Information and communication skills are the foundation of our modern technology society. Despite cultural and linguistic barriers, it is becoming increasingly important to be able to fall back on the universal structure of thought and action: logic.

The term molecular logic describes a field of research in which attempts are made to imitate logical connections with the aid of molecular systems, in solution or in solid phase. The most important requirement for this is that the system used shows a perceptible signal, for example in the form of light (absorption or emission), when stimulated in different ways. In other words, the molecular system used must be able to reversibly assume at least two distinct states, analogous to the states "on" and "off". Molecular logic is thus closely linked to the development and application of molecular switches, i.e. a compound class that fully fulfils these requirements.

Spiropyrans are a much researched substance class of molecular switches. These include the photochromic compound 1‘,3‘,3‘-Trimethyl-6-nitrospiro[chromen-2,2‘-indoline] (simplified as spiropyran). The compound can exist in two isomeric forms, the colourless spiropyrane and the less stable coloured merocyanine. The isomer merocyanine can be converted into a protonated MEH+ form with other photochromic properties in the presence of strong proton donors. Due to simple synthesis routes and commercial availability, good solubility in a variety of organic solvents, high chemical stability and, above all, its photochemical properties, it is ideally suited as a model substance for university and high-school education.

The main objective of this work was to develop didactically concise and scientifically consistent experiments with spiropyrane to introduce molecular logic into Chemistry classes and university courses. To achieve this goal, extensive photometric investigations with spiropyrane in solution and in solid matrix were carried out.

The knowledge gained from the photometric investigation of spiropyran in different solvents on the photochromic and thermal behaviour of the two merocyanine species ME and MEH+ could be used for the successful design and implementation of (min.) a meaningful example for all common gate variants (incl. a NAND coupling with fluoresceine, with the exception of a full adder). Each gate is designed so that ( i) chemicals suitable for school use can be experimented with, (ii) inexpensive experimental material can be used, (iii) the change in the output signal can be followed by the naked eye, and (iv) the light component is an important component.

The secondary goal of this work was the development of new interactive eLearning modules to illustrate structural and mechanistic basics in molecules and reactions, especially with the molecular switch spiropyrane/merocyanine. This goal was achieved by integrating several eLearning modules into the eLearning platform scheLM (special chemical eLearning modules) of the Heinrich-Heine-University Düsseldorf.

Get the thesis (in German): urn:nbn:de:hbz:468-20190221-103039-6

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