The form of the potential surface of the ground state was investigated on the basis of indoline spiropyran. As a result of this work the rotamers of an open-ring form of the spiropyran molecule were discovered, and the existence of the most probable rotamers was justified. The 3D potential surface of the ground state of the spiropyran molecule was built. The route of the isomerization of the molecule was discovered and values of barriers for this reaction were found. The part of the isomerization route that is responsible for changing the hybridization of spiroatom from sp3to sp2was found.

Spiropyran (SP) is a chromic material that undergoes isomerization to merocyanine (MC) under irradiation. To extend its applicability as a molecular switch, it would be convenient to be able to induce and control its isomerization also in the dark, what seems to be possible in acidic media. We present here a computational study of the mechanism of isomerization of protonated SP. We have found that protonation induces the stabilization of MC, protonated at O, relative to SP, protonated at N. Given the different site of protonation for both species, the ring-opening reaction must take place together with a proton transfer event. We have shown that the barrier of this process decreases if a protic solvent molecule take part in the reaction. In this way, the rate determining step of the process is the isomerization between different rotamers of protonated MC. The detailed knowledge of the reaction mechanism can help in the design of structural or electronic modifications of SP to improve its switchability.

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In this work, the possibility of creating a molecular switch based on the spiropyran (SP) molecule has been investigated. A class of molecules containing a nitro group in the benzopyran fragment was studied. In the indoline fragment NH2, NO2, H, and Cl were used in different positions as substituents. It has been shown that between the SP molecule and corresponding merocyanine (MC) molecule and an electrode material (Ag, Au, Pt, and Pd) it is possible to сreate a contact at the expense of a chemical bond. Such a cell will be stable in the absence of an external electric field. The SP molecule will turn into the MC molecule with the application of a uniform external field with a magnitude of E > 0.02 a.u. (a negative sign is on the indoline moiety). When the field E = 0.01 a.u. with another polarity is applied, the MC molecule relaxes into the SP molecule.

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