Fluorene fluorescence emission

Figure 28e suggests that fluorene 17 indeed underwent 2PA as evidenced by the slope of the plot of fluorescence emission intensity vs. several pump powers. It is particularly noteworthy that with this method of two-photon... 

Fig. 12 Normalized fluorescence emission spectra of PFO (black line), 9-fluorenone (red line) and the fluorene-fluorenone copolymer with 25% 9-fluorenone units (PF/FL0.25) (blue line)...

Fig. 13 Fluorescence emission spectra of fluorene-fluorenone copolymers with different 9-fluorenone fractions...

The synthesis of a polyfluorene with para-carborane in the backbone was reported (compound 63 in Figure 26.25). This polymer was found to be a blue Ught-anitting material. The monomer l,12-fcM(7-bromo-9,9-dihexyl-9H-fluoren-2-yl)-c/o50-l,12-dicarbadodecaborane was first synthesized and then polymerized via a Ni(0)-catalyzed dehalogenative polymerization. Shifts in UV absorption and fluorescence emission indicate some involvanent of the p-carborane clusters in extending the conjugation (Peterson et al., 2009). 

Pei and coworkers [362] synthesized fluorene copolymer functionalized with imidazole ligands in the side chains (270). The PL emission of 270 was sensitive to the presence of metal cations in solution (particularly efficient quenching was due to Cu2+), which makes it a promising material for fluorescent chemosensing. 

Intensive effort has been devoted to the optimization of CCP structures for improved fluorescence output of CCP-based FRET assays. The inherent optoelectronic properties of CCPs make PET one of the most detrimental processes for FRET. Before considering the parameters in the Forster equation, it is of primary concern to reduce the probability of PET. As the competition between FRET and PET is mainly determined by the energy level alignment between donor and acceptor, it can be minimized by careful choice of CCP and C. A series of cationic poly(fluorene-co-phenylene) (PFP) derivatives (IBr, 9, 10 and 11, chemical structures in Scheme 8) was synthesized to fine-tune the donor/acceptor energy levels for improved FRET [70]. FI or Tex Red (TR) labeled ssDNAg (5 -ATC TTG ACT ATG TGG GTG CT-3 ) were chosen as the energy acceptor. The emission spectra of IBr, 9, 10 and 11 are similar in shape with emission maxima at 415, 410, 414 and 410 nm, respectively. The overlap between the emission of these polymers and the absorption of FI or TR is thus similar. Their electrochemical properties were determined by cyclic voltammetry experiments. The calculated HOMO and LUMO... 

Steadily in the order 359, 385, 395, and 402 nm. The emission spectra exhibit a clearer vibrational fine structure than the absorption spectra. For spiro-sexiphe-nyl, 35b, a detailed analysis shows that the vibrational splitting of 0.20 eV corresponds to a phenyl breathing mode in the Raman spectrum [108]. If for spiro-sexiphenyl the outer biphenyl moieties are fixed parallel as in 4-Spiro (43), the absorption maximum is shifted from 346 to 353 nm (amorphous films) and the fluorescence maximum from 420 to 429 nm, maintaining the Stokes shift. The corresponding spectra are shown in Figure 3.17. The absorption signal at 310 nm in the spectrum of 43 can be attributed to the terminal fluorene moieties. The quantum yields for the fluorescence in the amorphous film are 38% for 35b and as high as 70 10% for 43 [89]. 

The time-resolved emission spectra (TRES) and fluorescence lifetimes, ti, of the fluorene derivatives were measured in liquid solutions at room temperature with a PTI QuantaMaster spectrofluorimeter with 0.1 ns temporal resolution [20]. At this resolution, all investigated fluorenes exhibited TRES which were coincident with the corresponding steady-state fluorescence spectra. As an example, TRES for compounds 3 and 11 in hexane, THE, and ACN are presented in Eig. 8 for different nanosecond delays 0 ns (curves 2,4,6) and 5 ns, which modeled the steady-state condition (curves 3,5,7). No differences in the fluorescence spectra for these two delays were observed, indicating that all relaxation processes in the first excited state Si are sufficiently fast for fluorene molecifles and did not exceed the time resolution of the PTI system ( 0.1 ns). 

The siimples were analysed by fluorescence spectroscopy at the conditions for each specific PAH [5] previously determined with the model compounds. The PAH studied are those listed by the US Environmental Protection Agency as priority pollutants [6] Fluorene, Benzo(a)Pyrene, Pyrene, Chrysene, Anthracene, Acenaphthene, Bezo(a)Anthracene, Dibenzo(a,h)Anthracene, Coronene, Perylene and Benzo(k)fluoranthene. In addition, Coronene emissions were also reported due to their important role on PAH stabilization at extreme conditions [7]. These 16 PAH were analysed from all runs in each of the four samples. 

Time-resolved fluorescence studies of fluorene-fluorenone copolymers in dilute toluene solution, enable us to identify different time regimes in the photoluminescence (PL) decay. Figure 18 shows the results of a maximum entropy method (MEM) analysis of the PL decays of fluorene-fluorenone copolymers [58] collected at the fluorene emission wavelength [66]. The different time regimes of the PL decay are associated with different kinetic species which migrate to the defects, most typically these are the CTS defects... 

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