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

Abstract

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.

Using calculations of the electronically excited states for investigation of fluorescent sensors: A review

“…The radiative lifetime from the SVP+ basis set is from 0.04 to 0.10 ns larger than that from the SVP basis set. [60,61] Unfortunately, these calculated values have not been validated with experimental data.…”

“…[58] Fluorescence lifetime (Ґf) is obtained from radiative lifetime (Ґr) and experimental fluorescence quantum yield (Φ) according to equation 2. [59] [60] In this way, R. Chidthong and co-workers calculated the radiative lifetime of a poly(fluorenepyridine) copolymer (FPy)n and a poly(fluorenephenylene) (FP)n ( figure 15). [60] The results of TD-B3LYP/SVP calculations show that the radiative lifetime is reduced from 0.84 to 0.40 ns for (FPy)n, and from 1.77 to 0.83 ns for (FP)n, when the oligomer chain is extended from n=1 to n=4.…”

“…[59] [60] In this way, R. Chidthong and co-workers calculated the radiative lifetime of a poly(fluorenepyridine) copolymer (FPy)n and a poly(fluorenephenylene) (FP)n ( figure 15). [60] The results of TD-B3LYP/SVP calculations show that the radiative lifetime is reduced from 0.84 to 0.40 ns for (FPy)n, and from 1.77 to 0.83 ns for (FP)n, when the oligomer chain is extended from n=1 to n=4. The radiative lifetime from the SVP+ basis set is from 0.04 to 0.10 ns larger than that from the SVP basis set.…”

A DFT study of charge-transfer and opto-electronic properties of some new materials involving carbazole units

“…That is, all molecules become more planar and possess a quinoid character in their lowest excited state[41]. We note the same inter-ring bonds length almost for oligomers e and f, whereas we observe a less value of C 25 -N 25' and C 1 -N 1' of compound d compared to those of e and f.Furthermore, in the middle of the backbone all structures tend to be more planar with dihedral angle about ߮~1°, while at the tow side of the chain we find almost the same values of angles ߠ at neutral state, which indicates the significant steric effect on geometrical properties.…”

Theoretical study on the structures and electronic properties of oligo(p-phenylenevinylene) carboxylic acid and its derivatives: effects of spacer and anchor groups

“…A quantitative understanding of molecular electronic excited states is important in many disciplines, including spectroscopy, photochemistry and the design of optical materials [15][16][17][18][19][20][21][22][23][24][25][26][27][28]. The prediction or interpretation of the discrete part of the spectrum is a demanding task for theoretical methods, especially for medium-and large-sized molecules.…”