Theoretical Investigation on the Luminescent Properties of Polyfluorene and Poly(fluorene-co-thiophene)

The density functional theory was employed to study the structures, ionization potentials（IPs）, electron affinities（EAs）, and HOMO-LUMO gaps（ΔH-L） of the oligomers. The time-dependent density functional theory（TD-DFT） and ZINDO were employed to study the lowest excitation energies（Egs） and the absorption and emission spectra of the oligomers of polyfluorene（PF） and poly（fluorene-co-thiophene）（PFT）. By extrapolating ΔH-L and Egs to those of infinite chain length, band gaps and effective conjugation lengths of the corresponding polymers were obtained. The IPs, EAs and 2abs of the polymers were obtained by extrapolating those of the oligomers to the inverse chain length equal to zero（I/n=0）. The outcome shows the decreased dihedral angle between fluorene and thiophene units in the PFT compared to that between fluorene units in the PF results in the increased efficient conjugation of PFT. These cause both the maximal absorption and emission wavelengths of PFT red-shifted compared with those of PF.

Luminescent Properties of Mercury-taining Diethynylfluorene Derivatives

Excited state structures and spectroscopic properties of mercury（ 11 ） complexes, Hg-TFT（1） and its electronwithdrawing substituents Hg-TFOT （ 2 ）, Hg-TFCNT （ 3 ）, where TFT = dietbynylfluorenyl, TFOT = diethynylfluorenone, and TFCNT = diethynyl-[9-（dicyanomethylene） fluorene], were studied using singlet excitation configuration interaction（CIS） and time-dependent density functional theory（TDDFT） methods. The results of the theoretical calculations indicate that the electron-withdrawing substitutions lead to a significant decrease in the energy gap between the ground state and the first excited states. In the case of Hg-TFCNT, the second singlet excited state （S2 ） may contribute to the luminescence because of its large S1-S2 separation.