The influence of nanoparticles on the excitation energies of the photochromic dihydroazulene/vinylheptafulvene system.

This paper studies how nanoparticles affect photochromic systems, focusing on the influence of gold nanoparticles on the optical properties of the dihydroazulene/vinylheptafulvene (DHA/VHF) system. This investigation is done using a combined quantum mechanical/molecular mechanical approach treating the photochromic system quantum mechanically. The gold nanoparticle is described as gold atoms with atomic polarizabilities using molecular mechanics, thus leaving out excitations of the gold nanoparticle. The photochromic molecule is described by density functional theory using the long-range corrected functional CAM-B3LYP and the correlation consistent basis set aug-cc-pVDZ. The results show that the optical properties of the photochromic system are affected by the presence of the nanoparticle. The vinylheptafulvene molecule is especially influenced, when increasing the interaction between the molecule and the gold nanoparticle. We observe that the optical properties of the photochromic system are influenced strongly by conformational changes, relative orientation compared to the gold nanoparticle, and the molecule-cluster distance. We observe that the different molecules are affected differently by the nanoparticle. Furthermore, we suggest that experiments should be carried out to investigate how the molecules coordinate to the nanoparticle.