A theoretical study of the excited-state decay of acylhydrazones

Abstract

Acylhydrazones is a novel yet underexploited class of molecular switches. In the present paper, we investigated the excited-state decay of three model systems of acylhydrazones in the gas phase by a combination of electronic structure calculations and Tully's surface hopping dynamic simulations. Our computational results demonstrated that the S 2 (n N p*) state decay of the three model systems leads to both the imine-like photo-isomerization through the S 1 (n N p*)/S 0 intersection and population of the S 1 (n O p*) state that will cross to the triplet manifold. The position of phenyl substituent was found to have an effect on the ratio of the two S 1 states. The present theoretical work provides some understandings of the intramolecular mechanism for de-population of the excited electronic states of acylhydrazones.acylhydrazones, internal conversion, intersystem crossing, molecular switches, photo-isomerization | I N T R O D U C T I O NMolecules that are able to undergo structural changes in response to light stimuli have attracted a great deal of interest because this type of molecules can be applied in a variety of functionalized materials. [1] The common photo-switchable molecules include azobenzenes, [2,3] diarylethene derivatives, [4,5] fulgides, [6] spiropyran and spirooxazine derivatives, [7,8] stilbenes, [9,10] catenanes and rotaxanes, [11,12] and molecular machines. [13][14][15] Hydrazones, structurally related to imines, are a class of compounds containing the C@NAN group, and also widely used in molecular switches, [16][17][18][19][20][21][22][23][24][25][26][27][28][29] and other fields of chemistry. [30][31][32][33][34][35][36][37][38][39][40] Recently, the effect of substitution type and position on the photochromic properties of acylhydrazones, characterized by the C@NAN and AC@O motifs, have been exploited experimentally by Hecht and coworkers. [41] They showed that acylhydrazones own advantages of remarkably facile preparation, highly fatigue resistance, and a higher degree of control over their properties. Also, under UV-irradiation, acylhydrazones were shown to exhibit good quantum yields (0.3-0.4 for E ! Z), which is between azobenzenes and diarylethenes in terms of efficiency. [42] Compared with hydrazones, acylhydrazone-based photoswitches pres-Int.