Fluorescence emissions and torsional conformations in pi-conjugated chains of PolyDCHD-HS

The fluorescence emission of polyDCHD-HS in solution at room and low temperature and as an amorphous film has been investigated. Extended segments along the polymer backbone are responsible for the observed fluorescence spectrum of polyDCHD-HS in benzene solution. Spectra of the polymer in cyclohexane solution and as an amorphous film give evidence of an additional red-shifted fluorescence, assigned to local substructures behaving as emission centers. Model calculations with the TD-DFT theoretical framework on planar and distorted enyne oligomers have allowed correlation of the S-0 -> S-1 transition energies to chain segments with different torsional angles around the C-C equivalent to C-C axis. In the ensuing structural model, benzene, molecules interact attractively with carbazolyl side groups of polyDCHD-HS, thus enhancing the chain rigidity. The interaction energy of carbazolyl groups with cyclohexane is smaller than that with benzene. This leads to more folded chains and, plausibly, also to clusters of few chain segments.