Substituent effects on the excited states of phenyl-capped phenylene vinylene tetramers

The singlet and triplet excited states of phenyl-capped tetramers of phenyl ene vinylene with different alkyl, alkoxy or cyano substituents, were inves tigated in benzene solution. The lowest singlet states were studied by lase r flash-photolysis with time-resolved microwave conductivity and fluorescen ce. The triplets were generated by pulse radiolysis, via energy transfer fr om the solvent excited singlet followed by inter-system crossing or by ener gy transfer from the naphthalene triplet. Their absorption spectra and rate s of quenching by oxygen were determined.