Abstract
Photoresponsive effects associated with two photochromic polyamides [poly(3,3′-azo dibenzoyl- trans-2,5-dimethylpiperazene) (I) and poly(4,4′-azo dibenzoyl- trans-dimethylpiperazene) (II)] are reported. (i) Langmuir film balance measurements show a reduction in area/monomer unit on changing from dark to light conditions and this is interpreted as being the result of trans→ cis isomerization. From detailed consideration of pressure-area curves for I and II, it is postulated that I exists as a helical structure whereas the structure of II is linear. (ii) I and II are also shown to exhibit a photoviscosity effect where the viscosity is reduced upon irradiation. This effect is discussed in terms of the postulated structures. (iii) The polymers also exhibit photomechanical properties. The photocontractile effect observed on switching off the radiation is attributed to incomplete isomerization of a fraction of the azo residues in locations within the polymer matrix.
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