2,5-bis(Arylethynyl)thienyl systems: Preparation and photophysical properties. Part II

A series of novel thienyl aryleneethynylenes have been prepared by the Sonogashira cross-coupling of dibrominated or diiodinated thiophenes with arylacetylenes. Previously we have investigated the properties of 2,5-bis(phenylethynyl) thiophene, BPET (1), [Siddle et al., New J. Chem., 2007, 31, 841] and in this work we go on to make chemical modification of the central thienyl moiety and examine their influence on the photophysical properties of the arylethynylene thienyl system. Room and low temperature absorption and emission spectra have been recorded, along with fluorescence quantum yields and lifetimes. It is demonstrated that the 1,1-dioxides (3b & 4b) exhibit significant broadening of their fluorescence spectra relative to the other systems, which we attribute to some degree of charge transfer from the peripheral phenyl rings into the electron-deficient thiophene-1,1-dioxide moiety. Furthermore, a non-conjugated fused thiophene system (6b) displays phosphorescence at low temperature, which is rarely observed from aryleneethynylenes. DFT and TD-DFT calculations have been performed to assist understanding the observed properties.