Structure, electronic and optical characterization of oligothiophenes terminated with (9H-fluoren-9-ylidene)methyl chromophores

The synthesis, spectral measurements and theoretical study of oligothiophenes terminated by (9H-fluoren-9-ylidene)methyl chromophores at the one (series AN) and both (series BN) ends are presented. The electron absorption and fluorescence spectra of prepared molecules were measured in polymer matrices and chloroform solution. The absorption and fluorescence spectra of the investigated systems are represented by broad band without vibrational structure. Well detectable fluorescence is observed for the compounds of the BN family. The experimentally observed medium large Stokes shifts (less than 5000 cm−1) indicate restricted geometrical changes in molecular chain upon optical excitation. Experimental lifetimes of fluorescence are shorter than 1 ns. Theoretical calculations have been performed at the semiempirical Austin Model 1 (AM1) and density functional theory (DFT) levels of the theory. The planarisation of dihedral angles between the fluorene and thiophene chromophores upon optical excitation theoretically was characterised, as well.