Ultrafast Intramolecular and Solvation Dynamics in 4,7-Bis (4,5-dibutylbenzo[1,2-b:4,3-b′]bisthiophene[1,2-b:4,3-b′]bisthiophen-2-yl)-2,1,3-benzothiadiazole

We report a combined approach of stationary and time-resolved fluorescence measurements and ultraviolet–visible (UV–vis) transient absorption spectroscopy (TAS) along with ab initio calculations, which provide an overall picture of the dynamics occurring after excitation in a push–pull molecule, namely, 4,7-bis (4,5-dibutylbenzo[1,2-b:4,3-b′]bisthiophene[1,2-b:4,3-b′]bisthiophen-2-yl)-2,1,3-benzothiadiazole. The analysis of the emission spectra in solvents of different polarities reveals the presence of three conformers whose structures differ in the orientation of the 4,5-dibutylbenzo-bisthiophene groups and in their planarity with respect to the benzothiadiazole acceptor group. The Kawski method allows us to estimate the ground- and first-excited state dipole moments (μg and μe) for the three conformers. We find values of μe similar for the three conformers and higher than the relative μg values as can be expected from a push–pull molecule undergoing a light-induced charge-transfer (CT) transition. UV–v...