Nanoscale physics

Spiropyran-Merocyanine isomerization under electron attachment
O. A. Kovalenko1, Yu.M. Lopatkin1, and P.O.Kondratenko2
1 Department of General and Theoretical Physics, Sumy State University, Rymsky-Korsakov St., 2,  Sumy  40007, Ukraine 
E-mail: olya.sumy.ua@gmail.com
2  Department of Theoretical Physics, Aerospace Institute, National Aviation University, Kosmonavt Komarov Prosp., 1, Kiev 03680, Ukraine

To date, studies of light-sensitive molecules are widely used. They find an application as molecular switches, thermal and chemical sensors, etc [1]. One of the brightest representatives of such molecules are spiropyrans (SP). There are two basic principles of molecular devices: photochromism and electrochromism. SP molecule satisfies these principles.
This work is devoted to investigation the reaction pathway of the anionic spiropyran-merocyanine isomerization.

Figure 1. Route of SPNH+→MCOH+ transformation. Energies are calculated on camb3lyp/cc-pvdz level of theory relatively to open TTC- form

In this work the reaction pathway for anionic SP-MC transformation has been studied. From Fig.1 it can be seen that the highest energy barrier corresponds to the cleavage of Cspiro-O bond and conversion from closed form to one of the merocyanine’s isomers. All isomers of merocyanine are more stable than SP, so the reverse MC-SP reaction cannot be spontaneous. It can be caused by visible radiation.  
Our results shows the possibility of ring opening and closure control using external inputs.

1.	 Singh R., Bohm M., Balasubramanian G. Energetic  and  structural  properties  of  different  conformations of  merocyanine  and  its  protonated  forms // Chem. Phys. Let.-2015.-633.-P. 287-291.