Effect of ring fusion on the electronic absorption and emission properties of oligothiophenes

A series of fused-ring oligothiophenes were synthesized by a combination of Stille and oxidative coupling reactions. Compounds with the same number of double bonds, but varying in extent of planarization, display a similar longest wavelength absorption maximum in solution. However, the introduction of sulfur linkages into these oligothiophenes leads to a blue shift of the maximum emission wavelength and a correspondingly smaller Stokes shift.