TY  - JOUR
A1  - Rietze, Clemens
A1  - Titov, Evgenii
A1  - Granucci, Giovanni
A1  - Saalfrank, Peter
T1  - Surface hopping dynamics for azobenzene photoisomerization
T2  - The journal of physical chemistry : C, Nanomaterials and interfaces
N2  - Azobenzenes easily photoswitch in solution, while their photoisomerization at surfaces is often hindered. In recent work, it was demonstrated by nonadiabatic molecular dynamics with trajectory surface hopping [Titov et al., J. Phys. Chem. Lett. 2016, 7, 3591-3596] that the experimentally observed suppression of trans -> cis isomerization yields in azobenzenes in a densely packed SAM (self-assembled monolayer) [Gahl et al., J. Am. Chem. Soc. 2010, 132, 1831-1838] is dominated by steric hindrance. In the present work, we systematically study by ground-state Langevin and nonadiabatic surface hopping dynamics, the effects of decreasing packing density on (i) UV/vis absorption spectra, (ii) trans -> cis isomerization yields, and (iii) excited-state lifetimes of photoexcited azobenzene. Within the quantum mechanics/ molecular mechanics models adopted here, we find that above a packing density of similar to 3 molecules/nm(2), switching yields are strongly reduced, while at smaller packing densities, the "monomer limit" is quickly approached. The UV/vis absorption spectra, on the other hand, depend on packing density over a larger range (down to at least similar to 1 molecule/nm(2)). Trends for excited-state lifetimes are less obvious, but it is found that lifetimes of pi pi* excited states decay monotonically with decreasing coverage. Effects of fluorination of the switches are also discussed for single, free molecules. Fluorination leads to comparatively large trans -> cis yields, in combination with long pi pi* lifetimes. Furthermore, for selected systems, also the effects of n pi* excitation at longer excitation wavelengths have been studied, which is found to enhance trans -> cis yields for free molecules but can lead to an opposite behavior in densely packed SAMs.
KW  - Computational chemistry
KW  - Energy
KW  - Molecules
KW  - Monomers
KW  - Oligomers
Y1  - 2020
UR  - https://publishup.uni-potsdam.de/frontdoor/index/index/docId/57892
SN  - 1932-7447
SN  - 1932-7455
VL  - 124
IS  - 48
SP  - 26287
EP  - 26295
PB  - American Chemical Society
CY  - Washington
ER  -