Urethane-substituted PDAs

A thermochromic phase transition of first order in which the energy of peak A shifts to lower energy in the high tenqperature phase is observed in partially polymerised crystals of PDA-DCH (47). The energies for peak A are similar to those for the urethane substituted PDAs, 1.8 and 2.6 eV, but the energies are reversed in the high and low tmi rature phases. In fully polymerised PDA-DCH the phase change is inhibited. This is in contrast to PDA-TS %diere the differences between the phase transition in the polymer and monomer are very small (48). 

We have attempted crystal growth of assorted diacetylenes by both liquid and vapor phase techniques. Urethane substituted diacetylenes are of particular interest because they are melt-stable and radiation polymerizable. Moreover, the polymer of the bis-ethylurethane of 5,7- dodecadiyn -1,12- diol (ETCD) exhibits the low energy ("excitonic") absorption peak found in the L-B PDA acid multilayer above and in poly-PTS, but is found in poly-TCDU at higher energy (32). Hence, we hoped to assess the role of this low energy absorption in nonlinear optical phenomena. 

The chromism observed in certain PDA systems (especially the urethane substituted polymers) requires structural study if the origin of these effects are to be established. Correlation of... 

Figure 11 (Left) Scheme of the polymerized bilayer assembly. The blue phase polydiyacetylene chromatic detection element is deposited over a support monolayer. The polydiacetylene chain Is asymmetrically substituted with urethane side groups partially terminated with receptor-binding ligands. (Right) Absorption spectrum of the blue and red phase PDA with a schematic representation of their chain with (red phase) and without (blue phase) influenza virus attached. Adapted figures with permission from D.H. Charych, J.O. Nagy, W. Spevak, and M.D. Bednarski, Sc/ence 261, 585 (1993), Figure 2 and 3. Copyright 1993 AAAS.

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