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(2,5)]-deca-3,7,9-triene with Mo(CHCMe3)(NAr)(OCMe3)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(N)(-2omega;omega,omega,0) and gamma(N)(0) varied with conjugation length to the 3.6 and 3.2 powers, respectively.