Density
Functional Theory Study of the Conformation and Optical Properties
of Hybrid Au<sub><i>n</i></sub>–Dithienylethene Systems
(<i>n</i> = 3, 19, 25)
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Abstract
We
present a theoretical study of Au<sub><i>n</i></sub>–dithienylethene
hybrid systems (<i>n</i> = 3, 19, 25), where the organic
molecule is covalently linked to a nanometer-scaled gold nanoparticle
(NP). We aim at gaining insights on the optical properties of such
photochromic devices and proposing a size-limited gold aggregate model
able to recover the optical properties of the experimental system.
We thus present a DFT-based calculation scheme to model the ground-state
(conformation, energetic parameters) and excited-state properties
(UV–visible absorption spectra) of this type of hybrid systems.
Within this framework, the structural parameters (adsorption site,
orientation, and internal structure of the photochrome) are found
to be slightly dependent on the size/shape of the gold aggregate.
The influence of the gold fragment on the optical properties of the
resulting hybrid system is then discussed with the help of TD-DFT
combined with an analysis of the virtual orbitals involved in the
photochromic transitions. We show that, for the open hybrid isomer,
the number of gold atoms is the key parameter to recover the photoactive
properties that are experimentally observed. On the contrary, for
hybrid closed systems, the three-dimensional structure of the metallic
aggregate is of high impact. We thus conclude that Au<sub>25</sub> corresponds to the most appropriate fragment to model nanometer-sized
NP–DTE hybrid device