Chemical Science , the flagship journal of the Royal Society of Chemistry, published an article by scientists and teachers at the Novosibirsk State University Department of Solid State Chemistry and the Institute of Solid State Chemistry and Mechanochemistry SB RAS. The article is devoted to the use of quantitative precise measurements of crystal bending during photoconversion. This research determines the kinetic transformation parameters at various temperatures for: activation energy, constant rate, feedback coefficient, etc. (Chizhik S., Sidelnikov A., Zakharov B., Naumov P., Boldyreva E. Quantification of Photoinduced Bending of Dynamic Molecular Crystals: From Macroscopic Strain to Kinetic Constants and Activation Energies, Chem. Sci., 2018).
In the 1980s three groups of Russian scientists (Novosibirsk, Novokuznetsk and Nizhny Novgorod/Gorky at the time) discovered simultaneously the ability of crystals from certain compounds to bend under the influence of light, heating or irradiation with light of a different wavelength, and resume their shape when the light is removed. Based on these observations, various options for photometers and sensors were proposed. This work is still relevant today. In Novosibirsk, research is being led by Elena Boldyreva, Doctor of Chemical Sciences, Head of the NSU Department of Solid State Chemistry, Honorary Doctorate from Edinburgh University and foreign member of the Academy of Sciences and Arts of Slovenia. In the 1990s, Boldyreva's research was supported by the Humboldt Foundation (Germany), the Royal Society of Great Britain, the National Council for Scientific Research of Italy, and the German Research Society. These results formed the basis for her doctoral dissertation, which she defended at 39 becoming, at that time, the youngest Doctor of Science in the SB RAS.
Boldyreva talked about growing interest in the topic.
– Since the beginning of the 2000s, research on photomechanical effects has developed in other countries. Now, every day an article describing the bending or torsion of a crystal under the influence of light appears in the most «prestigious» international journals. Most of the authors simply describe the «curious» phenomena they observed without digging deeper into the underlying processes. In this respect, the work of the Novosibirsk group is distinguished by its combination of deep knowledge of the physicochemistry process and the mechanics of materials. Every publication by the Novosibirsk group on this topic becomes an event that is praised by specialists and stimulates wider interest. This is reflected in the large number of readers and citations.
The success of the Novosibirsk group is possible thanks to the composition of its team. This includes A.A. Sidelnikov, PhD a researcher who is as good as Levsha, S.A. Chizhik PhD, a highly qualified physicist who understands the problems of solid state chemistry, and two chemists who understand non-routine crystallography methods, B.A. Zakharov Ph.D. and Boldyreva.
The Novosibirsk researchers previously published the most comprehensive review to date on the problems of photomechanical effects on crystals (Naumov P., Chizhik S., Panda M., Nath Naba K., Boldyreva E. Mechanically Responsive Molecular Crystals, ChemRev, 2015, 115 ( 22), 12440 –12490). There were also several publications presenting the results of their original research: Naumov P., Sahoo SC, Zakharov BA, Boldyreva EV, «Dynamic single crystals: Kinematic analysis of photoinduced crystal jumping (the photosalient effect)», Angewandte Chemie - International Edition, 2013, 252 ( 38), 9990-9995; Zhang, L., Chizhik, S., Wen, Y., & Naumov, P. , «Directed motility of hygroresponsive biomimetic actuators», Advanced Functional Materials, 2016, 26 (7), 10401053; Sidelnikov AA, Chizhik SA, Zakharov BA, Chupakhin AP, Boldyreva EV, «The effect of the thermal expansion on photoisomerization in the crystals of [Co (NH3) 5NO2] Cl (NO3): Different strain origins – different outcomes», CrystEngComm, 2016,18 (38), 7276 –7283).
Boldyreva described the breakthrough in their latest article:
– The current article in «Chemical Science» is unique even in relation to our previous publications. By measuring a crystal bending with the aid of a device designed and built by the researchers, we supplemented the results of measurements with data on structural changes obtained by diffraction of synchrotron radiation. This demonstrated for the first time how to obtain information on rate constant and activation energy of elementary processes inside crystals, and even calculate the absorption coefficients of light by individual molecules, depending on their position and orientation in the crystal. This was not possible before.
The study of crystal properties is important for both fundamental science and industry. Developments in this field have led to the creation of molecular machines (nanocar – a microscopic vehicle consisting of several molecules and capable of moving independently), molecular engines, photometers (optical analytical devices for quantifying the chemical composition of various samples), and mechanical drives.
The 2016 Nobel Prize in Chemistry was awarded to a group of researchers for their ability to stimulate and control the completely defined mechanical movements of individual molecules. The most interesting molecules are not yet material, the same as the most perfect cogs and gears are not yet a mechanism. In order to transfer chemo-mechanical phenomena to the macrocosm, it is necessary to learn how to create extended structures. The active elements of these structures, the molecules, would be placed in a specific way and function under the influence of external stimuli in a coordinated and controlled manner. It is important to proceed with research on macroscopic solid objects, films and crystals, in which photo, electro, and magneto mechanical effects are observed. If we analyze scientific journals published today, we see that interest is increasingly shifting towards the field of materials based on molecular crystals capable of reversibly changing their form and performing work under the influence of external influences. The scientists from NSU and the Institute of Solid State Chemistry SB RAS are working with great success on these challenges.
