Electronic transitions of fluorene, dibenzofuran, carbazole, and dibenzothiophene: From the onset of absorption to the ionization threshold

Single-Labeled Oligonucleotides Showing Fluorescence Changes upon Hybridization with Target Nucleic Acids

“…We have developed quencher-free MB probes that incorporate a 2-ethynylfluorene derivative covalently attached to a 2′-deoxyuridine residue ( U F ) ( Figure 12 ). Although fluorene ( FL ) derivatives provide a high fluorescence yield, they do not significantly affect the stability of the DNA duplexes because they have small volumes [ 49 , 50 , 51 , 52 , 53 , 54 , 55 ]. When an FL derivative was introduced at the C-5 position of deoxyuridine, the DNA containing it had little effect on the stability of the double-stranded DNA (dsDNA) formed upon hybridization with the complementary DNA [ 56 , 57 , 58 , 59 ].…”

A TD‐DFT basis set and density functional assessment for the calculation of electronic excitation energies of fluorene

“…The fluorene absorption spectrum in gas phase show three distinct groups of bands in the near ultraviolet, namely, a moderately intense band in the region of 300 nm, followed by a stronger band and more complex region (∼260 nm), and an even stronger set of bands near to 230 nm 5. These bands were previously assigned by polarized crystal transmittance and reflectance spectra29, 30 as A 1 (at 266, 202, 197, 162, and 130 nm) and B 2 (296, 255, 212, and 195 nm) symmetries 18. Vertical excitation energies of Rydberg states obtained at CASPT2/cc‐pVDZ level were attributed to three A 1 states: 181 (4 b 1 → 3 p x ), 190 (3 a 2 → 3 d xy ), and 169 nm (4 b 1 → 3 d xz ), and four B 2 states: 202 (3 a 2 → 3 p x ), 188 (3 a 2 → 3 d xz ), 173 (2 a 2 → 3 p x ), and 165 nm (3 b 1 → 3 d xy ) 16…”

“…The rigid and planar molecular structure of fluorene consisting of biphenyl units (Fig. 1) of C 2v symmetry and its unique photophysical properties, such as relatively large band gaps, low highest occupied molecular orbital (HOMO) energy levels, efficient polarized light emission, and intense violet fluorescence,17–22 have turned this chromophore into one of the most promising materials for photovoltaic applications,5, 23–26 dye‐sensitized solar cells, and two photon sensitizers with high quantum yields for use in photodynamic therapy 16, 27…”

“…Quantum chemical calculations of single units of π‐conjugated polymers can provide a fundamental understanding of the electronic structure of these molecules, and make a considerable contribution to the design of novel optoelectronic materials, because the electronic properties of a conjugated polymer are primarily governed by the chemical structure of its backbone 31, 32. Fluorene electronic excitations have been obtained at several levels of theory such as semiempirical,28, 29 time‐dependent density functional theory (TD‐DFT),16, 18 and multireference perturbation theory to the second order (CASPT2) 16. Vertical transitions obtained at TD‐DFT level using B3LYP/6‐31+G(d,p) show that predicted energies of the lowest B 2 and A 1 electronic transitions are at higher energy than experimentally observed, with an incorrect ordering of the 1 A 1 and 2 B 2 excited states 18.…”

“…Fluorene electronic excitations have been obtained at several levels of theory such as semiempirical,28, 29 time‐dependent density functional theory (TD‐DFT),16, 18 and multireference perturbation theory to the second order (CASPT2) 16. Vertical transitions obtained at TD‐DFT level using B3LYP/6‐31+G(d,p) show that predicted energies of the lowest B 2 and A 1 electronic transitions are at higher energy than experimentally observed, with an incorrect ordering of the 1 A 1 and 2 B 2 excited states 18. According to Ljubić and Sabljić16 calculations at CASPT2/cc‐pVDZ level, gives the observed sequence of the three lowest transitions (1 B 2 , 2 A 1 , and 2 B 2 ), while TD‐DFT using the hybrid density functional B3P86 and the basis set 6‐311+G(2d,p) fails to give the correct excited states sequence 18…”