Understanding the effects of packing and chemical terminations on the optical excitations of azobenzene-functionalized self-assembled monolayers

Abstract

In a first-principles study based on many-body perturbation theory, we analyze the optical excitations of azobenzene-functionalized self-assembled monolayers (SAMs) with increasing packing density and different terminations, considering for comparison the corresponding gas-phase molecules and dimers. Intermolecular coupling increases with the density of the chromophores independently of the functional groups. The intense [Formula: see text] resonance that triggers photo-isomerization is present in the spectra of isolated dimers and diluted SAMs, but it is almost completely washed out in tightly packed architectures. Intermolecular coupling is partially inhibited by mixing differently functionalized azobenzene derivatives, in particular when large groups are involved. In this way, the excitation band inducing the photo-isomerization process is partially preserved and the effects of dense packing partly counterbalanced. Our results suggest that a tailored design of azobenzene-functionalized SAMs which optimizes the interplay between the packing density of the chromophores and their termination can lead to significant improvements in the photo-switching efficiency of these systems.

Interplay between Intra- and Intermolecular Charge Transfer in the Optical Excitations of J-Aggregates

“…The intermolecular CT that characterizes both J and J CT is favored by the close molecular packing 82−84 of the aggregate, which enhances the electron delocalization between neighboring molecules as generally observed in optical excitations of organic crystals. 17,50,53,54,85,86 The reduction of LFE in the J-aggregate compared to the isolated monomer is due to the more homogeneous electron distribution in the crystal.…”

“…48,49 For example, in azobenzene-functionalized self-assembled monolayers, intermolecular interactions impact strongly on light absorption and excitonic coupling, and hence critically influence the photoisomerization process. 50−53 In these systems, intermolecular coupling and packing effects have been shown to be crucial also in core excitations. 54…”

Electronic and optical excitations of two-dimensional ZrS2 and HfS2 and their heterostructure

“…2) and represent the contributions to a given electronic transition to the λ th solution of the BSE (see, for example, Refs. [54][55][56]). Both eigenenergies and eigenvectors of Eq.…”

Azobenzene isomerization in condensed matter: lessons for the design of efficient light-responsive soft-matter systems

“…A similar effect can be achieved by mixing azobenzenes with different functionalizations, which partially inhibits coupling of the chromophores, therefore preserving some of the spectral features of the constituent monomers. 93 Fig. 4 displays the calculated optical absorption spectra of dimers and densely packed SAM (p-SAM) structures with mixed -H, -CN and -CF 3 para-functionalizations on the azobenzene core.…”

“…Hence, the presence of mixed functionalization partially counteracts the intermolecular coupling promoted by high molecular density. 93 Another useful method is the use of curvature to moderate azobenzene packing. This approach has been explored through adsorption of azobenzene thiols to planar Au (111) and curved Au nanoparticle surfaces.…”