Photochromics

Photochromic molecules are increasingly used in the design of innovative functional materials with applications in nanosciences, biology, and photonic devices. These compounds convert photonic energy into chemical energy on an ultrafast (picosecond) timescale to bring about a reversible transformation between two isomers. The change in electronic and molecular structures following electronic excitation results in a change of physical properties, which forms the basis of the applications listed above. The majority of the investigated photochromic compounds relies on the use of organic molecules such as azobenzenes or dithienylethenes. A photochromic system with remarkable properties, yet not as well known, is the dimethyldihydropyrene (DHP) molecule. Indeed, DHP can be quantitatively and reversibly isomerized into cyclophanediene (CPD) under visible light, but has also the singular property to be able to produce, store and release singlet oxygen (1O2) upon irradiation at low energy under aerobic conditions. 1O2 is of major interest particularly for medical purposes. Other photochromic compounds based metal complexes have also been discovered. This is the case of ruthenium nitrosyl complexes (Ru-NO), which can be photoisomerized in their isonitrosyl form (Ru-ON). These complexes also have the remarkable property to have the capability to photorelease nitric oxide (NO•), which plays an important role in many physiological mechanisms. It thus appears that DHP and Ru-NO derivatives display remarkable and complementary properties. However, these compounds have not been much exploited yet and their underlying photoswitching mechanism and releasing capability of biologically active species remain poorly understood. The PHOTOCHROMICS project plans to intimately associate DHP and Ru-NO units in order to design hybrid DHP-Ru-NO multifunctional compounds. The objectives are the design of i) multiphotochromic compunds and ii) bimodal molecular systems capable of producing simultaneously 1O2 and NO• by photoinduced stimuli. Indeed, the design of switchable molecular architectures that can exist in several stable states is a growing field. Similarly, the possibility to produce at the same time the 1O2 and NO• biologically active species, which both display remarkable antibacterial properties, is of tremendous interest in the medical field, as synergistic effects have already been observed. This proposal gathers theoretical and experimental chemists. Original hybrid compounds will be synthesized using technics in organic synthesis and coordination chemistry. The properties of the different states involved in the multiphotochromic systems and the production / activation of 1O2 and NO• will be analyzed by spectroscopic, photophysical, photochemical and electrochemical studies. A major task will be the rationalization of the underlying mechanisms involved. We will use advanced computational methodologies beyond the current state-of-the-art, which will allow static and dynamic investigations of these systems in their environment. The main originality of this proposal lies in the remarkable properties and complementarity of the DHP and Ru-NO derivatives, whether in the field of photochromism or in the activation of small molecules of biological interest. To merge these two units in hybrid systems represent a formidable opportunity, which constitutes the heart of this project. The PHOTOCHROMICS proposal is a fundamental research project whose expected results will bring significant progress in the understanding of the involved systems. However, if the end results proved to be full of promise, the designed compounds might be exploited for application purposes in the future.