Photophysical properties of bis(2,2′-bithiophene-5-yl)benzenes

The synthesis of three kinds of bis(2,2′-bithiophene-5-yl)benzenes (1,2-, 1,3- and 1,4-bis(2,2′-bithiophene-5-yl)benzene; o-PhBT2, m-PhBT2 and p-PhBT2) and analyses of their photophysical properties are reported. The electronic structures were also studied by the molecular orbital (MO) method. It was found that the extension of π-conjugation varies with the substitution mode (o-, m-, or p-), which in turn influences the absorption, fluorescence and transient absorption spectra. The unique behaviour of o-PhBT2 was interpreted in terms of its lowest unoccupied MO (LUMO) pattern, in which π-orbitals on the adjacent sulfur atoms in each bithienyl moiety can have considerable overlap.