Multi-addressable photochromic terarylene containing benzo[b]thiophene-1,1-dioxide unit as ethene bridge: multifunctional molecular logic gates on unimolecular platform

Abstract

A photochromic terarylene (BTO) containing a benzo[b]thiophene-1,1-dioxide unit as a central ethene bridge was synthesized and characterized, and exhibits good thermal stability and fatigue resistance both in solution and bulk crystals. When triggered by chemical ions, protons and light, BTO can behave as an absorbance and fluorescence switch, leading to a multi-addressable system. The different color changes of BTO upon adding Cu²⁺ and Hg²⁺ ions arise from the relative binding stoichiometry and the association affinities. The titration of the Job plot indicates that BTO forms a 1 : 1 complex with Hg²⁺, whereas in the case of Cu²⁺, the Job plot exhibits a maximum at about a 0.33 mole fraction, indicating that BTO forms a 2 : 1 complex with Cu²⁺. Moreover, the conversion yield of BTO can be modulated with chemical ions. Impressively, an increase in conversion yield was observed by adding Hg²⁺ to the solution of BTO, that is, the conversion yield and cyclization quantum yield are increased from 77.6% and 28.5% (for BTO only) to 99.8% and 43.1% (BTO-Hg²⁺), respectively. A series of molecular logic gates such as a half-adder, half-subtractor, 4-to-2 encoder, 2-to-4 decoder, and a 1 : 2 demultiplexer were constructed on the unimolecular platform by employing absorption and emission properties at different wavelengths as outputs, with the appropriate combination of chemical and photonic stimuli, which is a further step towards data processing on the molecular level with potential applications in sensing and labeling as well as for data manipulation.