Smart fluorescent molecular switches based on boron

A molecular switch is a molecule that works in response to external stimuli, such as B. a change in pH, light or electric current, can be reversibly shifted between two or more stable states. These molecules are of interest in the nanotechnology field for use in molecular computers or reactive drug delivery systems. When in either state (on / off) the molecule fluoresces, the compounds are called fluorescent molecular switches and their applications are even more interesting in the life sciences field, especially when they can work in small spaces. For example, they can be used for biosensors and as imaging probes in cells.

Scientists from the Barcelona Institute of Materials Science (ICMAB, CSIC) and the Universitat Autònoma de Barcelona (UAB) have developed a series of extremely stable fluorescent molecular switches that can be controlled electrochemically by the application of a potential. This is possible due to the presence of a very specific redox-active anion – a negatively charged molecule that oxidizes and reduces very quickly. In this case the anion is the so-called COSAN anion (its full name is cobalt bisdicarbollide and chemical formula [3,3′-Co(C₂B₉H₁₁)₂]^{– –} ), a boron cluster-based complex with a Co (III) center that has the unusual property of self-assembling into vesicles and micelles.

These systems are the first examples of intelligent redox-controlled fluorescent molecular switches obtained from compounds based on boron clusters. Because of the presence of the COSAN, they are extremely stable, soluble in a large number of organic solvents, and show a large reversible fluorescence modulation. In addition, these molecules can self-assemble to form gels with 1D nanostructures, which in some cases preserves the luminescence behavior.

This research is the result of a collaboration between Dr. Rosario Núñez from the Laboratory for Inorganic Materials and Catalysis (LMI) at ICMAB-CSIC and Dr. Jordi Hernando from the Electrochemistry, Photochemistry and Organic Reactivity Group (GEFRO) in the Chemistry Department at UAB. The experience of the LMI group at ICMAB in the chemistry, electrochemistry and photoluminescence of materials based on boron clusters and the experience of the GEFRO group at UAB in the investigation of the luminescence and electrochemical properties of fluorescent dyes such as perylene derivatives came together in a very positive one Synergy that has made it possible to combine the special features of both research areas in order to produce these new intelligent molecules with outstanding electro-optical behavior.

“Due to the presence of COSAN, the properties of these compounds clearly demonstrate their ability to act as redox-induced fluorescent switches that could be used in the design of molecular storage and information processing devices, biosensor and imaging probes, or electrofluorochrome displays,” says Rosario Núñez, researcher at ICMAB.

“In addition, these systems outperform previous systems based on conjugates of perylenediimides with other metal-based redox units such as ferrocene. On the one hand, they show greater reversible fluorescence modulation with minimal degradation, while their solubility in polar media is dramatically improved, an essential requirement for future applications in biological systems, “explains Jordi Hernando, researcher at UAB.

Borate-based passivation layers enable reversible calcium batteries

More information:
Laura Parejo et al. Reversibly switchable fluorescent molecular systems based on metallacarborane-perylenediimide conjugates, Chemistry – A European magazine (2020). Doi: 10.1002 / chem.202002419

Provided by the Autonomous University of Barcelona