Abstract

Through a combined quantum mechanics/molecular mechanics (QM/MM) approach, we evaluate the photodynamics of the mono- and dithiolated azobenzenes when they are chemisorbed on a gold surface. The analysis of steric effects suggests that the presence of the surface influences the photoisomerization process of the chemisorbed monothiolated azobenzene. In particular, the trans → cis quantum yields decrease, and the nπ* state lifetimes become longer. The approach to the twisted conical intersection needed for the isomerization is hindered when the molecule is attached to a substrate because of the van der Waals interactions with the surface. For the cis isomer, the cis → trans photoisomerization quantum yield is almost unaffected, since this isomer is not flat, and thus the interaction with the surface is less remarkable. Dithiolated azobenzene can photoisomerize both trans → cis and cis → trans, also when doubly linked to the surface, preserving the two bonds with the gold atoms: the flexibility of the centra...

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