Effect of interchain coupling on conducting polymer luminescence: Excimers in derivatives of poly(phenylene vinylene)

Optical excitation of a chain in a polymer film may result in formation of an excimer, a superposition of on-chain excitons and charge-transfer excitons on the originally excited chain and a neighboring chain. The excimer emission is redshifted compared to that of an on-chain exciton by an amount depending on the interchain coupling t_⊥. Setting up the excimer wave function and calculating the redshift, we determine average t_⊥ values, referred to a monomer, of 0.52 eV and 0.16 eV for poly(2,5-hexyloxy p-phenylene cyanovinylene), CN-PPV, and poly[2-methoxy, ${5{-}(2}^{{'}}{-}ethyl{-}hexyloxy){-}1$, 4 $p$-phenylene vinylene], MEH-PPV, respectively, and use them to determine the effect of interchain distance on the emission.