Nonlinear optical analysis of a series of triblock copolymers containing model polyenes: the dependence of hyperpolarizability on conjugation length

Sequential ring-opening metathesis polymerization of norbornene and 7,8-bis(trifluoromethyl)tricyclo[4.2.2.0[sup 2.5]]-deca-3,7,9-triene with Mo(CHCMe[sub 3])(NAr)(OCMe[sub 3])[sub 2] (Ar = 2,6-diisopropylphenyl) followed by linking termination with a conjugated dialdehyde results in highly soluble A-B-A triblock copolymers containing an oligomer of a precursor of Durham polyacetylene as the central block. Subsequent heat treatment converts the polyacetylene precursors into model polyenes. A series of these copolymers that had conjugation lengths ranging from 4 to 16 double bonds was synthesized. The polyenes were isomerized to the predominantly all-trans isomer. The presence of the polynorbornene chains solubilizes the polyenes, allowing their hyperpolarizability to be probed with electric field induced second harmonic generation; [gamma][sub N]([minus]2[omega][sup [sm bullet]],[omega][omega],0) and [gamma][sub N](0) varied with conjugation length to the 3.6 and 3.2 powers, respectively. 54 refs., 8 figs., 4 tabs.