The molecular switches : types and applications

A subject of this work is group of organic compounds known as molecular switches. Molecular switches are described as chemical compounds which molecules have at least two thermodynamically stable states. Conversion between these states is reversible and may be induced by such factors as change of the temperature or flow of the electric current or irradiation of the molecule with the light of particular wavelength [1]. Especially interesting are photochromic molecular switches. In this group the conversion is triggered by irradiation with a light of a particular wavelength [2]. Because of its unique properties, this type of compounds is extensively studied by the scientists, who investigate their photochromic properties as ways of using them in coordination with lanthanide metals and construction of novel molecular materials [3]. Especially interesting group of photochromic molecular switches is class named diarylethenes. This type of compounds after irradiation with UV light undergo cyclization, which is reversible under light of the visible spectrum (Figure 1). The other important group of photochromic molecular switches is class of compounds possessing in their structure chiroptic unit. The irradiation of the molecule with left- and right-handed circularly polarized light leads to change of the absolute configuration (Fig. 8) [1]. This type of switches may be used in construction of synthetic molecular motors which is widely studied subject nowadays [1]. The other groups of molecular switches are host- guest molecular switches and mechanically- interlocked molecular switches. In the first mentioned before group the bistable states differ in their affinity for guests (Fig. 15) [14]. The second one is based on the group of compounds named catenanes and rotaxanes. They can be described as two chemical individuals, mechanically interlocked in each other, which are not connected with chemical bonds (Fig. 19). This kind of molecular switches are used in construction of the logic gates [1]