Deep-blue emission

Despite the remarkable quantum yield and the relatively short emission decay time of Ir(4,6-dFppy)2(acac), much less research work has been published than for the related famous compound Ir(4,6-dFppy)2(pic) (FTrpic, pic = picolinate), which exhibits a 15 nm blue shifted emission compared to Ir(4,6-dFppy)2(acac) [50, 53], Therefore, Ir(4,6-dFppy)2(pic) is a more suited dopant for highly desired blue-emitting OLEDs [17, 54-56], It is noted that by the implementation of strongly electron-withdrawing ancillary ligands, further shifts towards a deep blue emission could be achieved [45, 57, 58],... 

As depicted in Figure 5.5 PFs in film display an unstructured, long absorption maximum centered at 3.3 eV. The photoluminescence emission spectrum of PFs shows a vibronic fine structure with an energetic spacing of 180 meV (stretching vibration of the C = C-C = C structure of the polymer backbone) with the transition at 2.9 eV yielding a deep blue emission. In dilute solution the spectra are very similar to that of the solid state and only a small bathochromic shift of 20 meV is typically observed for both absorption and emission. 

Recently, Venkatesan reported the platinum(II) complexes 108—110 (Fig. 37), whose structures are similar to complexes of type 100 the three complexes differ for the ancillary chelating dicarbene Hgand and for the phenylacetylide coordinated moieties.AH the complexes display a deep blue emission, in solution (dichloromethane at room temperature), in rigid matrix (2-methyltetrahydrofuran at 77 K), in soHd state, and in PMMA film (doped with 10% of the platinum complex). The emission maxima are in the... 

Many other PF copolymers, which do not contain a particularly electron-active moiety, but nevertheless, can improve the performance of the material in PLED have been synthesized. The Huang group [364,365] at Institute of Materials Research and Engineering (IMRE, Singapore) synthesized deep-blue copolymer 272 by Suzuki copolymerization of fluorene-diboronic acid with dibromobenzene. The emission band of 272 has a peak at 420 nm and a well-defined vibronic feature at 448 nm with a fwhm of 69 nm, and virtually no green emission,... 

Recently, Chen s group reported a deep blue OLED based on an asymmetric mono(styryl) amine derivative DB1 (192) as shown in Scheme 3.59. PL spectra of this deep blue dopant in toluene solution showed a peak emission of 438 nm, which is about 20 nm hypsochromic shift compared with DSA-amine symmetric dopant, due to the shorter chromophoric conjugated length of the mono(styryl) amine. OLED device based on this blue dopant achieved a very high efficiency of 5.4 cd/A, with CIE coordinates of (0.14, 0.13) [234]. 

Dramatic advances in modem fluorophore technology have been achieved with the introduction of Alexa Fluor dyes by Molecular Probes (Alexa Fluor is a registered trademark of Molecular Probes). Alexa Fluor dyes are available in a broad range of fluorescence excitation and emission wavelength maxima, ranging from the ultraviolet and deep blue to the near-infrared regions. Because of the large... 

Minor conjugation limits the emission band to the deep-blue color range (/.max — 420 40 nm) (03MI1351). PTV, the polymer 585 (02MI200), is a fluorescent material. The UV/Vis spectrum of the oligomers showed the 0-0 transition at 487 nm (03AM306). 

Other hyperbranched polymers showed similar absorption and luminescence properties. Upon photoexcitation, the hb-PA solutions emitted deep-blue to blue-green lights, whose intensities were higher than that of poly(l-phenyl-l-octyne), a well-known highly emissive polyene. The PL efficiencies of the polymers varied with their molecular structures. Polymers hb-P(38-VI), hfo-P(45-V), hb-P(48-VI), M>-P(50-VI), fcfo-P(50-VII) and hb-P(59-VI) exhibited (P values higher than 70%, with hfc-P(50-VII) giving the highest value of 98%. 

From the PPP-related materials, especially the oligomerpara-hexaphenyl (PHP) (see Fig. 8.2) seems to be very suitable for such an external energy conversion process. This is due to the highly efficient EL devices, which can be fabricated based on PHP and due to the deep blue PHP emission with an emission maximum located at 425 nm.104 With that material, a substantial increase of the efficiency and a reduction of the onset voltages has been achieved in multilayer structures (see Sec. 8.3.3).105,106... 

One of the reasons fluorene is appealing is its efficient emission of ultraviolet or deep blue light. Terfluorenes have several emission maxima at around 393, 412, and 441 nm [2]. The photoluminescent quantum yields, solid films [2]. However, most oligofluorenes have a photoluminescence quantum yield in the range from 40 to 70% [35,54,60,141 ]. 

The performance achieved by these devices was record-setting, with each of their characteristics independently superior to reported values from any other polarized OLEDs, including those using polyfluorenes [9-13]. Recently, an integrated polarization ratio of 31 has been reported but with an efficiency of 0.3 cd A-1 for a deep blue OLED comprising poly(9,9-dioctylfluorene) [198]. Two other papers have reported polarization ratios at their emission maxima of 25.7 [199] and 29 [200], which are still slightly lower than 31.2 reported for the blue dodecafluorene device [196]. 

The emission energies of Ir complexes with cyclometallated ppy ligands cannot be raised into the deep blue and near-UV part of the spectrum (A ,ax <450 nm) through the use of electron-withdrawing and -donating substituents. 

Phosphorus is analyzed by atomic absorption and ICP emission spectrometry and neutron activation techniques. The total phosphorus contents can be estimated colorimetrically by classical wet methods (American Public Health Association... 1995). Phosphorus is oxidized to orthophosphate by digesting with potassium persulfate. The solution is treated with ammonium molybdate and antimony potassium tartarate in an acid medium to form an antimony-phosphomolybdate complex that is reduced by ascorbic acid to form a deep blue coloration, the intensity of which is proportional to the concentration of phosphorus. The absorbance is measmed at 650 nm by a spectrophotometer. Alternatively, it can be analyzed colorimetrically by an autoanalyzer (Technicon model). 

Changing the chemical structure of the cyclometalating (C N) ligand allows easy control of the color of phosphorescent emission. Efficient phosphorescent OLEDs with various lr(in)-based dopants emitting in a wide range of colors from deep red to deep blue have been demonstrated and will be discussed in the following sections. 

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