Issue 22, 2016

Connectivity matters – ultrafast isomerization dynamics of bisazobenzene photoswitches


We have investigated the ultrafast dynamics of o-, m- and p-bisazobenzenes, which represent elementary building blocks for photoswitchable multiazobenzene nanostructures. The connectivity pattern within bisazobenzenes and the ensuing complex interactions between the individual azobenzene units determines the ultrafast dynamics of these compounds and their photochemical properties. While retaining a relatively high EZ isomerization quantum yield, o-bisazobenzene exhibits a very high thermal relaxation rate (half-life of 1.6 ms). Our theoretical calculations reveal that the geometry allows intramolecular excitonic interaction between the azobenzene units, which is reflected in the femtosecond transient absorption data via the simultaneous bleaching of the two excitonic bands. In contrast, the properties of m-bisazobenzene are very similar to the monomeric azobenzene, with the two units acting nearly independently from each other. The highest degree of π conjugation extending over the two azobenzene units was observed for p-bisazobenzene, which results in strong planarity of the molecule, reduced excited state lifetime and relatively low isomerization quantum yield. Multiphotochromic systems bridge the gap between molecular photoswitches and macroscopic function and thus, understanding the properties of bisazobenzenes opens the way to the design and development of new structures with extensive and versatile applications.

Graphical abstract: Connectivity matters – ultrafast isomerization dynamics of bisazobenzene photoswitches

Supplementary files

Article information

Article type
27 Jan 2016
05 Mar 2016
First published
09 Mar 2016
This article is Open Access
Creative Commons BY license

Phys. Chem. Chem. Phys., 2016,18, 14795-14804

Connectivity matters – ultrafast isomerization dynamics of bisazobenzene photoswitches

C. Slavov, C. Yang, L. Schweighauser, C. Boumrifak, A. Dreuw, H. A. Wegner and J. Wachtveitl, Phys. Chem. Chem. Phys., 2016, 18, 14795 DOI: 10.1039/C6CP00603E

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