Certain molecular switches respond to input stimulations producing detectable outputs. The interplay of these signals can be exploited to reproduce basic logic operations at the molecular level. The transition from simple logic gates to complex digital circuits requires the design of chemical systems able to process multiple inputs and outputs. We have identified a three-state molecular switch that responds to one chemical and two optical inputs producing two optical outputs. We have encoded binary digits in its inputs and outputs applying positive logic conventions and demonstrated that this chemical system converts three-digit input strings into two-digit output strings. The logic function executed by the three-state molecular switch is equivalent to that of a combinational logic circuit integrating two AND, two NOT, and one OR gate. The three states of the molecular switch are a colorless spiropyran, a purple trans-merocyanine, and its yellow-green protonated form. We have elucidated their structures b...

Digital processing with a three-state molecular switch.

This review is part of a continuing study of the many applications of van der Waals radii (WR) in various fields of chemistry, and especially in crystal chemistry and stereochemistry. An analysis of relevant publications has shown that WR systems are used most often and most successfully in studies of the conformation of molecules, though their original source is usually an analysis of intermolecular contacts. This review will deal with traditional applications of WR and with some some new aspects, inducing the geometrical modelling of chemical reactions and new types of specific intermolecular interactions. The bibliography includes 149 references.

New applications of van der Waals radii in chemistry

A comparison of the solution and solid state thermal decay kinetics of five photochromic spiropyrans with different N-alkyl groups (SP1–SP5) was carried out in acetonitrile and nanocrystalline suspensions at 298 K. The change in absorbance at ca. 550 nm was measured as a function of time for the merocyanine (MC) using transmission UV–vis spectroscopy. We found that the thermal decay kinetics are slower and follow a biexponential decay in the solid state compared to a faster, monoexponential decay that was measured in solution. We observed that, while the kinetic range measured in solution varies by a factor of 13, the decay kinetics in the solid state cover a range of ca. 150, indicating that crystal packing has an influence much greater than that of the effects of N-alkyl substitution. A fluorescence analysis of irradiated samples of SP1 in solution could be used to determine the formation of the MC species and its subsequent decay. By contrast, a similar analysis of nanocrystalline suspensions displayed...

Transmission Spectroscopy and Kinetics in Crystalline Solids Using Aqueous Nanocrystalline Suspensions: The Spiropyran-Merocyanine Photochromic System

K. Sh. Karaev

Papers

Crystal and molecular structure of the photochromic spiropyran 1-benzyl-3,3-dimethyl-6′-nitrospiro ([2H-1]-benzopyran-2′,2-indoline)

Crystal and molecular structures of 4-hydroxy-5-nitrophenyl cyclohexyl ketone

Crystal and molecular structure of telluraxanthene C13H10Te and 9,9′-trans-bis(telluraxanthenyl) C26H18Te2