Abstract
Azobenzene-containing molecules may associate with each other in systems such as self-assembled monolayers or micelles. The interaction between azobenzene units leads to a formation of exciton states in these molecular assemblies. Apart from local excitations of monomers, the electronic transitions to the exciton states may involve charge transfer excitations. Here, we perform quantum chemical calculations and apply transition density matrix analysis to quantify local and charge transfer contributions to the lowest electronic transitions in azobenzene dimers of various arrangements. We find that the transitions to the lowest exciton states of the considered dimers are dominated by local excitations, but charge transfer contributions become sizable for some of the lowest electronic transitions in stacked and slip-stacked dimers at short intermolecular distances. In addition, we assess different ways to partition the transition density matrix between fragments. In particular, we find that the inclusion of the atomic orbital overlap has a pronounced effect on quantifying charge transfer contributions if a large basis set is used.
Highlights
Azobenzene is arguably the most famous molecular switch, which is widely employed in numerous applications at the nanoscale [1]
Association of azobenzene units occurs in self-assembled monolayers of azobenzene-containing molecules [3,4], in micelles of azobenzene-functionalized surfactants [5,6], and in aggregates formed upon surfactant complexation with polymers, such as DNA [7,8]
Recent years have seen the emergence of covalently connected multiazobenzene molecules such as bisazobenzenes [9] and mixed dimers [10], star-shaped trimers [11,12,13] and tetramers [14], macrocycles [15] and molecular rings [16], tailored to applications ranging from energy storage [17] to wavelength-selective control of molecular switching [18]
Summary
Azobenzene is arguably the most famous molecular switch, which is widely employed in numerous applications at the nanoscale [1]. In many systems employing azobenzene-containing molecules, azobenzene units may interact with each other, which, in turn, may affect their photophysical and photochemical properties. Association of azobenzene units occurs in self-assembled monolayers of azobenzene-containing molecules [3,4], in micelles of azobenzene-functionalized surfactants [5,6], and in aggregates formed upon surfactant complexation with polymers, such as DNA [7,8]. Nanoscale architectures including azobenzene-functionalized carbon nanotubes [19] and metal-organic frameworks incorporating azobenzene [20] have been realized
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