Triphenylene Diazocines: Butterfly-Type Rigid Photoswitches with Annulated Aromatic Ring Systems and Increased Switching Amplitude

TL;DR

This paper introduces new photoswitches with large aromatic rings that can be used in materials science for applications like liquid crystals and polymers.

Contribution

The integration of triphenylene groups into diazocines creates photoswitches with the largest annulated aromatic ring systems reported.

Findings

Triphenylene diazocines show increased switching amplitude and visible-range switching wavelengths.

The new photoswitches avoid side reactions seen in azoanthracene and can be easily synthesized.

The 4-fold substituted system is suitable for use in polymers, COFs, and MOFs.

Abstract

Azobenzenes are arguably
the most frequently used photoswitches,
but systems in which the benzene units are replaced by larger π
systems are rare. Azonaphthalene is known, but the next higher homologue
azoanthracene already undergoes irreversible intramolecular cycloaddition
during photoisomerization. Such side reactions are not possible with
rigid diazocines. In the present work, we have succeeded in integrating
triphenylene groups into diazocines, making them the azo switches
with the largest aromatic, annulated ring systems published to date.
Both the unsubstituted system and several derivatives are easy to
access. The extension of the π systems results in a larger molecular
switching amplitude compared to parent diazocine, which should lead
to better force transmission to the environment in material applications.
The switching wavelengths are shifted bathochromically into the visible
range, although the photostationary equilibria are decreased. Potential
applications include switchable liquid crystals, mechanophores, photoactuators,
and many other responsive materials. Particularly noteworthy is the
4-fold substitution of the system, which allows incorporation into
larger systems, e.g. as multifunctional cross-linkers in polymers
or as building blocks in COFs and MOFs.

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