Acta Physico-Chimica Sinca  2018, Vol. 34 Issue (10): 1171-1178    DOI: 10.3866/PKU.WHXB201803024 Special Issue: Molecular Simulations in Materials Science
 ARTICLE
Influence of Photoisomerization on Binding Energy and Conformation of Azobenzene-Containing Host-Guest Complex
Pingying LIU1,2,Chunyan LIU2,Qian LIU2,Jing MA2,*()
1 School of Materials Science and Engineering, Jingdezhen Ceramic Institute, Jingdezhen 333403, Jiangxi Province, P. R. China
2 School of Chemistry and Chemical Engineering, Key Laboratory of Mesoscopic Chemistry of MOE, Nanjing University, Nanjing 210023, P. R. China

Abstract

The construction of a photo-controllable artificial molecular machine capable of realizing the light-driven motion on a molecular scale and of performing a specific function is a fascinating topic in supramolecular chemistry. The bistable switchable molecule, azobenzene (AZO), has been introduced into the supramolecular architecture as a key building block, owing to its efficient and reversible trans (E)-cis (Z) photoisomerization. The binding strength of the dibenzo[24]crown-8 (DB24C8) host and dialkylammonium-based rod-like guest consisting of an AZO moiety and the Z$\to$E photoisomerization process in an interlocked host-guest complex have been investigated by the density functional theory (DFT) calculations and the reactive molecular dynamics (RMD) simulations by considering both torsion and inversion paths. The strong host-guest binding strength provides a necessary premise to stabilize the complex during the E-Z photoisomerization of the AZO unit, which is a terminal stopper to control the directional motion of the guest. A stronger binding strength for the Z isomer can be induced by the stronger hydrogen-bonding interaction. The steric effect is introduced into the Z isomer to force the ring slipping exclusively over the cyclopentyl terminal (pseudostopper). The host-guest complexation has a slight effect on the conformation of the AZO functional subunit for the two isomers. The faster Z$\to$E photoisomerization process within the picosecond timescale is kinetically more favored than the dethreading of the ring through the pseudostopper subunit of the rod. After isomerization, a structure relaxation is observed for the crown ether ring within 500 ps. The flexible backbone of the crown ether ring is helpful in realizing steady and stable host-guest recognition during photoisomerization. Moreover, the orthogonality of the site-specific binding interaction is revealed by the similar binding energies obtained at similar hydrogen bonding recognition sites for various interlocked host-guest supramolecular systems although the constituents of the guests are different from each other. The introduction of two stereoisomers of the AZO subunit has little influence on the other conformations of guest subunits. These results are useful for the rational design of more sophisticated stimuli-controlled artificial molecular machines.

Received: 25 December 2017      Published: 02 March 2018
 MSC2000: O641
Fund:  the National Natural Science Foundation of China(21673111);the National Natural Science Foundation of China(21661017);Natural Science Foundation of Jiangxi Province, China(20161BAB203081)
Corresponding Authors: Jing MA     E-mail: majing@nju.edu.cn