Abstract
Alternating oligomers and polymers consisting of 2,2′-bipyridine and diethinylenebenzene units and corresponding model compounds were synthesized and investigated in dilute solutions by absorption spectroscopy and by stationary and time-resolved emission spectroscopy. The strictly linear (rod-like) π-chain oligomers/polymers were compared with the angularly linked oligomers/polymers and with related model compounds. The model compounds which already show the essential spectroscopic properties of the oligomers/polymers consist of three (hetero)aromatics linearly connected by two diethenylene groups. These models exhibit fluorescence quantum yields close to unity and short fluorescence decay times around 1 ns. Fluorescence anisotropy and rotational relaxation times are consistent with the Stokes–Einstein equation and the Perrin equation. The absorption and emission spectra of the polymers and their radiative rate constants determined by fluorescence quantum yield and lifetime and according to the Strickler/Berg equation show a conjugation length of one to two repetition units. The conjugation along the chain is stronger in linear than in angular polymers and stronger in alkoxy-substituted than in unsubstituted polymers. In angular polymers at least two different emitting segments were found. The shortened mean lifetimes and the reduced fluorescence quantum yields and anisotropies of the oligomers/polymers indicate an additional radiationless deactivation channel which is opened by energy migration along the chain. Rates of energy transfer calculated for linear and angular polymers correlate with rates of radiationless deactivation. Copyright © 2000 John Wiley & Sons, Ltd.
Published Version
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