Near-infrared emission polymers

Ghoroghchian PP, Frail PR, Susumu K, Park TH, WU SP, Uyeda HT, Hammer DA, Therien MJ (2005) Broad spectral domain fluorescence wavelength modification of visible and near-infrared emissive polymersomes. J Am Chem Soc 127 15388-15390 Ghoroghchian PP, Jin JJ, Brannan AK, Frail PR, Bates FS, Therien MJ, Hammer DA (2006) Quantitative membrane loading of polymer vesicles. Soft Matter 2 973-980 Pata V, Ahmed F, Discher DD, Dan N (2004) Membrane solubilization by detergent resistance conferred by thickness. Langmuir 20(10) 3888-3893... 

By contrast electron-rich heteroaromatic units such as 2,5-pyridines or 2,5-thiophenes provide a way to redshift the emission of PAVs (Figure 4.5). The lower symmetry of the pyridine than the phenylene ring means that poly(pyridine vinylene) can be produced as a random polymer or in two regioregular forms—head-to-tail (35) and head-to-head (36) [74]. The EL emission maxima of these appear at 575, 584, and 605 nm, respectively. The thiophene-containing copolymer 37 has even more redshifted emission (Amax = 620 nm) [107,108]. The most redshifted emission yet to be reported from PAV is near-infrared emission (Amax = 800 nm) from the polymers 38 (Amax = 740 nm) [109] and 39 (Amax=800 ntn) [110,111]. A wide range of other heteroaromatic units have been incorporated into PAVs with emission colors ranging from green to red. 

Poly(3-cyclohexyl-4-methylthiophene) (PCHMT) (39) (Fig. 4) and poly(3-cyclo-hexylthiophene) (PCHT) (36) have been made by the FeCl3 method in order to test these polymers as polymers LEDs [108]. The PCHMT gave an Af of 72K (PDI 2.8) and a film A ax of 303 and PCHT had an A/, of 56K with a very large PDI of 9 and a film A ax of 426 nm, with 77% HT couplings. It was found that by varying the steric environment of the PT, that LEDs having from blue to near-infrared emission could be made. 

Raman spectroscopy has been widely used to study the composition and molecular structure of polymers [100, 101, 102, 103, 104]. Assessment of conformation, tacticity, orientation, chain bonds and crystallinity bands are quite well established. However, some difficulties have been found when analysing Raman data since the band intensities depend upon several factors, such as laser power and sample and instrument alignment, which are not dependent on the sample chemical properties. Raman spectra may show a non-linear base line to fluorescence (or incandescence in near infrared excited Raman spectra). Fluorescence is a strong light emission, which interferes with or totally swaps the weak Raman signal. It is therefore necessary to remove the effects of these variables. Several methods and mathematical artefacts have been used in order to remove the effects of fluorescence on the spectra [105, 106, 107]. 

The mechanism for the SPAN layer changing the emission properties of the PPy VPV polymer is attributed to the formation of new emissive species due to protonation of the pyridyl units by SPAN. These species was identified by both absorption and PL experiments. Figure 9.15 shows the absorbance spectra of a PPy VPV layer, a SPAN layer, and a bilayer of PPy VPV/SPAN. SPAN is a self-doped, water-soluble conducting polymer with a room-temperature conductivity of 10-2 S/cm.18 It has a wide optical window from green to near infrared PPy VPV... 

The emission color of PAVs depends crucially on the nature of the arylene unit. Replacement of a phenylene with an oligophenylene unit produces a blue-shift in the emission, e. g. the poly(pentaphenylene vinylene) 58 is a blue emitter (2rnax = 446 nm) [71], while heterocydes induce red-shifts. This is particularly marked in the case of thiophene so that the polymer 59 actually emits in the near-infrared (7m lx = 740 nm) [72]. The picture with fused polycyclic aromatics is more complicated with the 1,4-naphthalene 19 [73] and 9,10-anthracene 60 [74] polymers both being markedly red-shifted in emission compared with PPV (1), while the 2,6-napthalene 18 [75] and 3,6-phenanthrene 61 [58] materials are slightly blue-shifted. 

Phthalocyanine and naphthalocyanine are guest dye dopants suitable for the near infrared (IR) region. PVK is used as usual, as the hole transport polymer, Alqs, or a sulforamide derivative (Al(qs)3) is used as the host dye. The absorbance spectra of the guest dyes are significantly different from the emission spectra of the host dyes. However, the high molar absorption of the host dye dopants result in such efficiencies of energy transfer that are comparable to quinacridone or rubrene dopants. 

See also Activation Analysis Neutron Activation. Atomic Absorption Spectrometry Principles and Instrumentation. Atomic Emission Spectrometry Principles and Instrumentation. Chromatography Overview Principles. Gas Chromatography Pyrolysis Mass Spectrometry. Headspace Analysis Static Purge and Trap. Infrared Spectroscopy Near-Infrared Industrial Applications. Liquid Chromatography Normal Phase Reversed Phase Size-Exclusion. Microscopy Techniques Scanning Electron Microscopy. Polymers Natural Rubber Synthetic. Process Analysis Chromatography. Sample Dissolution for Elemental Analysis Dry... 

Since the mid-1990s, there has been plenty of activity regarding the use of spectroscopic techniques for on-line evaluation of polymer properties [143-146]. This has been possible due to the recent development of fiber-optic probes, which allow in-situ measurements in remote and harsh environments (high temperatures, pressures, toxic environments, and so on). An additional advantage is that a fiber-optic probe can be installed in an existing reactor within a short time without expensive modifications. Fluorescent, ultraviolet (UV), infrared (IR), near-infrared (NIR), mid-infrared (MIR) and Raman spectroscopic techniques can be used for polymerization reaction monitoring. These can be divided between absorption- and emission-based techniques. IR, NIR, and MIR are absorption-based. 

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