[functional molecule] molecular data storage: multimode optical / thermal controlled macrocyclic compounds

Multimode optical switch refers to molecules with various forms of existence under external stimulation They have attracted wide attention in the fields of molecular electronic devices, optical data memory, molecular machines, sensors and solar energy storage by virtue of their ability of multi-state conversion When multiple molecules with switching characteristics are combined, their ability is far more than 1 + 1 But when multiple switches are combined, they often face another problem: how to control one switch alone? If all switches are controlled by one signal, no matter how many switches are combined, they can only change two states from 0 to 1 If several switches are controlled by the same signal or affected by each other, the accuracy of the system will also be fatally affected Fig 1 Gibbs free energy of isomers of macrocyclic compounds (image source: angel Chem Int ed., 2018, 57, 6069) Recently, Professor Mogens br ø ndsted Nielsen from the Department of chemistry, University of Copenhagen synthesized a multi-mode ring molecule, which has multiple controllable switches and can realize the transformation of different molecular States through light and heat stimulation 。 DHA / VHF system and cis / trans - AZB system have been the favorite in the field of molecular switch Combining the advantages of these two kinds of molecules, a macrocyclic compound with a single azobenzene unit and two chamomile units was synthesized, and the state transition of the macrocyclic compound was regulated by the light / heat response of each unit This achievement was published in German Applied Chemistry (DOI: 10.1002 / anie 201712942) under the title of "multistate photoswitches: macrocyclic dihydroazulene / azobenzeneaggregates" Fig 2 synthesis route (left) and crystal structure (right) of macrocyclic compounds (photo source: angelw Chem Int ed., 2018, 57, 6069) synthesis of macrocyclic compounds is not complex Acyl chloride substituted azobenzene (1) and glycol compound (2) can be cyclized in the presence of DMAP to obtain macrocyclic compounds (Fig 2, left) Although the target compounds have diastereomers (A and b) by separation, their UV-Vis absorption spectra are very similar, which will not have a great impact on the subsequent results In addition, the author has obtained a single crystal (trans AZB DHA DHA b) of one of the non enantiomers The crystallographic data show that the compound does not exist in the form of monomer, but in the form of a dimer of cyclocyclo Fig 3 transformation from trans AZB DHA DHA to CIS AZB VHF VHF (left); change of absorbance with irradiation time (middle); transformation from CIS AZB VHF VHF to trans AZB VHF VHF (right) (photo source: angel Chem Int ed., 2018, 57, 6069) The author first tested the light conversion of trans AZB DHA DHA DHA with the lowest energy under 365 nm light, The UV absorption of trans-azb-dha-dha at 300-400 nm continued to decrease, while that at 420-620 nm continued to increase (Fig 3, left) By comparing the changes of UV absorption of azobenzene and chamomile under light conditions, it can be proved that the changes are caused by the CIS trans transformation of azobenzene and the transformation of DHA / VHF Based on the data of UV absorption, the conversion rate of DHA to VHF is 86% In addition, the kinetic test results show that the transition from DHA to VHF is independent of the CIS trans change of azobenzene (Fig 3, middle) However, since the conversion of VHF to DHA cannot be controlled by light, only trans AZB VHF VHF, a macrocyclic compound transformed by azobenzene, can be obtained by illuminating CIS AZB VHF VHF (Fig 3, right) Fig 4 transition from trans-azb-vhf-vhf to trans-azb-dha-dha (left); UV absorption of trans-azb-vhf-vhf and cis-azb-vhf-vhf over time (right) (source: angel Chem Int ed., 2018, 57, 6069) Since the transition from VHF to DHA is controlled by heat, it can be controlled separately from the transformation of azobenzene However, there are two VHFs in the molecule, so the author would like to know whether the conversion of the two VHFs can be carried out separately The results show that the change of UV absorption is not a continuous process in the transition process from trans / cis-azb-vhf-vhf to trans / cis-azb-dha-dha Therefore, the authors conclude that the conversion rate of the first VHF to DHA is not the same as that of the other VHF to DHA (Fig 4, left) In addition, the effect of azobenzene on the conversion rate was studied The results showed that the presence of azobenzene had no effect on the conversion of the first VHF, but the conversion rate of VHF to DHA containing trans azobenzene was nearly three times faster than that of CIS azobenzene Finally, the author said that although the synthesized molecules are expected to be used in the field of data storage, the current molecules can only store three bytes of information, which is a long way from practical application All authors: Alexandru vlasseanu, MADS koerstz, Anders b.skov, Kurt v Mikkelsen, and Mogens br ø ndsted Nielsen