Systematic Modulation of Hydrogen Bond Donors in Aminoazobenzene Derivatives Provides Further Evidence for the Concerted Inversion Photoisomerization Pathway

A series of aminoazobenzene derivatives structurally related to AzoAMP‐1 have been prepared and characterized by using a variety of analytical techniques. AzoAMP‐1 is based on 2,2′‐diaminoazobenzene with N ‐methylpyridine groups. The new derivatives all contain a hydrogen bond between the aniline hydrogen atom and the azo group, as well as a separate pendant functional group that could contribute an additional hydrogen‐bond acceptor to an intramolecular network. A combination of photoisomerization studies and NMR spectroscopic and X‐ray crystallographic investigations suggest that AzoAMP‐1 possesses a unique structure that prevents isomerization through the concerted inversion pathway, which cannot be reproduced with other types or arrangements of substituents. Only AzoAMQ, which contains a similar quinolone heterocycle in place of the pyridine group of AzoAMP‐1, displayed somewhat similar photochemistry.