AbstractThe title compound (P) was synthesized via Pd‐ and Cu‐catalyzed coupling reactions (Sonogashira reaction). Two model compounds prepared by similar synthetic routes, 1,4‐bis(2,2′‐bipyridin‐5′‐ylethynyl)‐2,5‐di(2‐ethylhexyl)oxybenzene (M), and 5,5′‐[1‐ethynyl‐4‐(2,2′‐bipyridin‐5′‐ylethynyl)‐2,5‐di(2‐ethylhexyl)oxybenzene]‐2,2′‐bipyridine (D), were included in the spectroscopic investigations for comparison. As a result of steady‐state and time‐resolved absorption and fluorescence investigations in solution and in solid films, we conclude that the π‐conjugation is restricted by torsional motions of the aromatic chain segments at ordinary temperature. It comprises about 2–3 repetition units in the S1 state as concluded from a comparison of the experimental radiative rate constant with that calculated from the Strickler–Berg relation. It is even less in the ground state. The theoretical limit obtained from DFT calculations is about twice as large for the ideal coplanar conformation. Whereas the π–π stacking interaction in pure polymer films is very weak in the ground state, it is significantly stronger in the S1 state, giving rise to excimer fluorescence. Energy migration along the polymer backbone is inefficient. Intermolecular energy migration and transfer to embedded acceptors becomes efficient in solid films. Copyright © 2004 John Wiley & Sons, Ltd.