Structural and electronic properties of poly(fluorene–vinylene) copolymer and its derivatives: Time-dependent density functional theory investigation

Theoretical study of the alkoxyls groups effect on PPV-ether excited states, a relationship with femtosecond decay

Based on Density Functional Theory (DFT), the effect of alkoxyl substituents groups on the excited states of new PPV derivative (PPV-ether) are studied. Thus differences on the relaxation energy, the atomic charge distribution and the conjugation length at their excited state are interpreted on the pathways of the nature on the emissive species. Photoluminescence and optical spectra of the corresponding modeling structures are carried out. Furthermore, the life time at the excited state are emphasized either theoretically from oscillator strength or experimentally from time resolved photoluminescence.

Excited state properties, fluorescence energies, and lifetimes of a poly(fluorene-phenylene), based on TD-DFT investigation

The structural and electronic properties of fluorene-phenylene copolymer (FP)(n), n = 1-4 were studied by means of quantum chemical calculations based on density functional theory (DFT) and time dependent density functional theory (TD-DFT) using B3LYP functional. Geometry optimizations of these oligomers were performed for the ground state and the lowest singlet excited state. It was found that (FP)(n) is nonplanar in its ground state while the electronic excitations lead to planarity in its S(1) state. Absorption and fluorescence energies were calculated using TD-B3LYP/SVP and TD-B3LYP/SVP+ methods. Vertical excitation energies and fluorescence energies were obtained by extrapolating these values to infinite chain length, resulting in extrapolated values for vertical excitation energy of 2.89 and 2.87 eV, respectively. The S(1) <-- S(0) electronic excitation is characterized as a highest occupied molecular orbital to lowest unoccupied molecular orbital transition and is distinguishing in terms of oscillator strength. Fluorescence energies of (FP)(n) calculated from TD-B3LYP/SVP and TD-B3LYP/SVP+ methods are 2.27 and 2.26 eV, respectively. Radiative lifetimes are predicted to be 0.55 and 0.51 ns for TD-B3LYP/SVP and TD-B3LYP/SVP+ calculations, respectively. These fundamental information are valuable data in designing and making of promising materials for LED materials.