TUNING OF FLUORESCENCE IN FILMS AND NANOPARTICLES OF OLIGOPHENYLENEVINYLENES

Oligophenylenevinylenes (OPV) with a series of distance-controlling, e lectron-donating, and/or electron-withdrawing substituents are deposit ed from vapor phase and solution as ultrathin films or nanoparticles w ith diameters of 20-200 nm. In some cases the systems are doped at lev els of 10(-5)-10(-3) with energy accepting OPV's of longer chainlength s. Absorption and fluorescence spectra, steady-state and time-resolved anisotropies, and radiative and nonradiative deactivation rates of th ese systems are investigated and compared to the corresponding propel ties in dilute solutions. Fluorescence yields of the parent oligomers and their alkyl or oxyalkyl derivatives are high in solution with an ' 'infinite chain'' limit of Phi(F) approximate to 0.5 and an upper radi ative rate constant limit of k(r)(infinity) = (1 +/- 0.3) x 10(9) s(-1 ). Yields and k(r) decrease strongly in films and nanoparticles becaus e of H-aggregate fort-nation. However, doping with fluorescent accepto rs can increase the yields up to Introduction of electron-withdrawing -CN and -SO2CF3 substituents reduces Phi(F) in low viscous dilute solu tions almost to zero, High viscosities and condensation to solid phase s will raise the yields up to Phi(F) --> 0.6 because of suppression of nonradiative torsional deactivation and formation of J-aggregates wit h high k(r).