Molecular-level study of photoorientation in hydrogen-bonded azopolymer complexes
Article [Accepted Manuscript]
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Macromolecules ; vol. 51, no. 3, pp. 1077-1087.Publisher(s)
American Chemical SocietyAbstract(s)
To optimize azobenzene-containing materials for applications such as
rewritable waveguides and holographic data storage, it is imperative to understand the effect
of the azobenzene structure on the photoresponse of the material. Supramolecular materials,
in which a complexed photoactive azobenzene controls the motion or other properties of a
passive polymer, are uniquely convenient for studying the impact of specific chemical
modifications. Here, we use polarization modulation infrared structural absorbance
spectroscopy (PM-IRSAS) to hydrogen-bonded supramolecular azobenzene complexes
using poly(4-vinylpyridine) (P4VP) as a model polymer. We show that changing the tail
group from hydrogen (AH) to cyano (ACN) induces greater angular redistribution of the
chromophores and, remarkably, provokes P4VP pyridine ring orientation. Increasing the
degree of complexation decreases the saturated orientation of both AH and ACN, whereas for
P4VP/ACN it increases the pyridine orientation as well as the orientation stability of both
components. These results explain the contrasting photoinduced birefringence behavior
previously observed for these complexes and identify azo-azo intermolecular interactions as
the main reason. To our knowledge, this is the first molecular-level spectroscopic analysis of
the contrasting contributions of azobenzenes to the photo-orientation of supramolecular
azopolymer complexes and the first report of the large impact of small molecular changes on
the capacity of azo dyes to transfer light-induced orientation to a photopassive polymer.
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