Fluorescence Quantum Yield of Poly(p-phenylenevinylene) Prepared via the Paracyclophene Route:  Effect of Chain Length and Interchain Contacts

The monomer 9-[( tert -butyldimethylsilyl)oxy][2.2]paracyclophan-1-ene ( 1 ) is polymerized by Mo(NAr)(CHCMe 2 Ph)(OCMe(CF 3 ) 2 ) 2 (Ar = 2,6-diisopropylphenyl) in a living manner. Block copolymers containing poly( 1 ) and polynorbornene (poly(NBE)) can be prepared and have narrow polydispersities. Treatment of poly( 1 ) with NBu 4 F produces poly(9-hydroxy[2.2]paracyclophan-1-ene) which dehydrates to poly( p -phenylenevinylene) (PPV) under mild conditions. Block copolymers containing segments of size-specific and defect-free PPV with poly(NBE) of various dimensions can be prepared readily and are soluble in a variety of common organic solvents. These polymers serve as excellent candidates to measure the effect of chain length and frequency of interchain contacts on PPV's fluorescence quantum yield (Φ f ). Solution and solid-state quantum yield determinations, coupled to fluorescence lifetime measurements, reveal an acute drop in Φ f as the degree of polymerization of the emissive species increases and as the average distance between PPV chains decreases. PPV x - block -poly(NBE) y prepared in solution consistently shows larger Φ f than material prepared by solid-state dehydration. The poly(NBE) companion block also serves to protect PPV from atmospheric degradation.