Conjugated polymers with 2,2 '-bipyridine and diethinylenebenzene units: absorption and luminescence properties

Alternating oligomers and polymers consisting of 2,2'-bipyridine and diethi nylenebenzene units and corresponding model compounds were synthesized and investigated in dilute solutions by absorption spectroscopy and by stationa ry and time-resolved emission spectroscopy. The strictly linear (rod-like) pi-chain oligomers/polymers were compared with the angularly linked oligome rs/polymers and with related model compounds. The model compounds which alr eady show the essential spectroscopic properties of the oligomers/polymers consist of three (hetero)aromatics linearly connected by two diethenylene g roups. These models exhibit fluorescence quantum yields close to unity and short fluorescence decay times around I ns. Fluorescence anisotropy and rot ational relaxation times are consistent with the Stokes-Einstein equation a nd the Perrin equation. The absorption and emission spectra of the polymers and their radiative rate constants determined by fluorescence quantum yiel d and lifetime and according to the Strickler/Berg equation show a conjugat ion length of one to two repetition units. The conjugation along the chain is stronger in linear than in angular polymers and stronger in alkoxy-subst ituted than in unsubstituted polymers. In angular polymers at least two dif ferent emitting segments were found. The shortened mean lifetimes and the r educed fluorescence quantum yields and anisotropies of the oligomers/polyme rs indicate an additional radiationless deactivation channel which is opene d by energy migration along the chain. Rates of energy transfer calculated for linear and angular polymers correlate with rates of radiationless deact ivation. Copyright (C) 2000 John Wiley & Sons, Ltd.