Conformational analysis and electronic transition of carbazole-based oligomers as explained by density functional theory

Smooth heuristic optimization on a complex chemical subspace

In the present work, several heuristic reordering algorithms for deterministic optimization on a combinatorial chemical compound space are evaluated for performance and efficiency.

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.