Emission properties

FIGURE 8.8. Site-selective photoluminescence spectra of para-hexaphenyl at 10 K emission spectra at excitation energies of 3.30 (top curve), 3.21, 3.14, 3.04, and 3.01 eV inset evolution of the emission peaks versus excitation energy the dotted line represents the quantum energy of the exciting photons.(Reproduced from Ref. 164. and 165.) 

Another absorbing species present both in photo excited and electrically excited para-phenylenes are polarons. In Fig. 8.9, we have summarized the absorption and emission spectra encountered in para-hexaphenyl (1) the triplet absorption, (2) the stimulated emission observed in time-resolved experiments with a 200-fs resolution, (3) the polaron absorption, and (4) the continuous-wave photoluminescence emission. A clearer picture for the polaronic state can be derived from experiments on the ladder-type PPPs. 

FIGURE 8.9. The solid line peaking at 1.78 eV (1) describes the triplet continuous-wave (cw) absorption spectrum of hexaphenyl squares (2) represents the femtosecond pump/probe spectra at zero delay between pump and probe (solid line to guide the eye), (3) the polaronic absorption peaks at at 2.3 eY, and (4) the cw emission spectrum of peaks at roughly 2.9 eV. 

FIGURE 8.10. Doping-induced (C), charge-induced (B), and photoinduced (A) absorption in a ladder-type PPR 

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Similar to MTBE, TAME is used as gasoline additive for its high octane rating and its ability to reduce carbon monoxide and hydrocarbon exhaust emissions. Properties of oxygenates used as gasoline additives are shown in Table 5-2. °... 

Alloys with thoria (Th02> are used for TIG (Tungsten Inert Gas) welding electrodes and in electronic applications where its increased electron emission properties and high temperature strength prove advantageous. 

Regarding the emission properties, AM I/Cl calculations, performed on a cluster containing three stilbene molecules separated by 4 A, show that the main lattice deformations take place on the central unit in the lowest excited state. It is therefore reasonable to assume that the wavefunction of the relaxed electron-hole pair extends at most over three interacting chains. The results further demonstrate that the weak coupling calculated between the ground state and the lowest excited state evolves in a way veiy similar to that reported for cofacial dimers. 

There have been numerous studies of the electrical and emission properties of conjugated polymer-, small molecule-, and molecularly doped polymer-based OLEDs. The current-voltage and radiance-voltage characteristics have been nica sured as a function of thickness of the organic layer, temperature, different metal electrodes, etc. in an attempt to understand the device physics. A major factor in hibiting progress is the purity of the organic impurities that are incorporated dur-... 

At this stage, we can draw several important conclusions regarding the absorption and emission properties of cofacial dimers formed by two identical PPV chains ... 

The possibility of controlling ihc morphological and structural order in the solid is therefore a fundamental requirement for the control and reproducibility of the emission properties of a luminescent material within an organic light emitting diode (OLED) device. 

Significant stimulated emission is only found for the pristine side of the sample. From these results it was concluded that the photoinduccd absorption that suppresses die stimulated emission is directly or indirectly caused by the presence of oxygen-related defects. It was shown earlier that the effect of photooxidation on the emission properties of PPV can be explained by the formation of carbonyl-groups that act as sLrong electron acceptors leading to an efficient dissociation of the plioh excited slate 29). It can be concluded that the dissociated pair near the defcci leads to the strong photoinduccd absorption. The observation that... 

Thompson, J. F., et al. (1997). Mutation of a protease-sensitive region in firefly luciferase alters light emission properties. J. Biol. Chem. 272 18766-18771. 

V.S. Fomenko, Emission Properties of the Elements and Compounds, Izd. Naukova Dumka, Kiev, 1964. 

As a final note, during the final stages of preparing this review the first example of a diphosphene-PPV was reported [111]. This exciting new polymer contains P=P bonds spaced by p-phenylenevinylene units in the main chain, has a degree of polymerization of approximately 6, and shows emissive properties. 

Yersin H (2004) Triplet Emitters for OLED Applications. Mechanisms of Exciton Trapping and Control of Emission Properties. 241 1-6 Yeung LK,see Crooks RM (2001) 212 81-135... 

The discriminatory emission properties between two-coordinate d ° gold(I) complexes and their respective three-coordinate counterparts have been demonstrated in the literature [6, 10-13]. As discussed in the later sections, Che and coworkers have rationalized that the extraordinarily large Stokes shift of the visible emission of [Au2(diphosphine)2] from the [5da 6pa] transition is due to the exciplex formation ofthe excited state with solvent or counterions [6]. Fackler [14—16] reported the photophysical properties of monomeric [AUL3] complexes, which show visible luminescence with large Stokes shifts (typically lOOOOcm ), suggesting significant excited-state distortion. Gray et al. [10] examined the spectroscopic properties of... 

The trinuclear gold(I) complexes [(AuX)3( j,-triphos)] (triphos = bis(2-diphenylphos-phinoethyl)phenylphosphine X = Cl, Br, I, CgFs ), where X = Br and I , were reported to emit at room temperature with emission energies significantly red-shifted from that ofthe free phosphine ligand (2477 cm for Br with Agx 350 nm 4482 cm for I with Aex 385 nm) [41]. The chloro, pentafluorophenyl, and l,3,5-tris(trifluor-omethyl)phenyl derivatives do not emit, even at Aex <300 nm. The emission properties... 

Vandegrift, A.E., Shannon, L.J. Particulate Pollutant System Study. voL II, Handbook of Emission Properties, NHS, National Technical Information Service, Commerce Department PB 203522, Springfield, Va., 197 1. 

The high-spin/low-spin interconverison in a Ni11 complex of the cyclam derivative (639) bearing a luminescent naphthalene substituent has been used as a fluorescent molecular thermometer.161 The Ni11 tends to quench fluorescence of the proximate naphthalene subunit, but the two spin states exert a different influence on the emission properties. Emission is temperature dependent, since the high spin —> low spin conversion is endothermic, i.e., a temperature increase favors formation of the low-spin form. 

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