Tunable emission and

The general principle of detection of free radicals is based on the spectroscopy (absorption and emission) and mass spectrometry (ionization) or combination of both. An early review has summarized various techniques to detect small free radicals, particularly diatomic and triatomic species.68 Essentially, the spectroscopy of free radicals provides basic knowledge for the detection of radicals, and the spectroscopy of numerous free radicals has been well characterized (see recent reviews2-4). Two experimental techniques are most popular for spectroscopy studies and thus for detection of radicals laser-induced fluorescence (LIF) and resonance-enhanced multiphoton ionization (REMPI). In the photochemistry studies of free radicals, the intense, tunable and narrow-bandwidth lasers are essential for both the detection (via spectroscopy and photoionization) and the photodissociation of free radicals. 

A modified SILAR system has been used to grow CdSe in CdS/CdSe core shell semiconductor nanocrystals.12 A cadmium precursor solution, with CdO dissolved with oleic acid in octadecane, was injected onto the substrate, and the Se solution (Se powder dissolved with tributylphosphine in octadecane) was similarly injected. The temperature of the reaction solution was 185 °C. A CdS outer layer in the CdS/CdSe/CdS colloidal quantum wells was deposited by alternating injections of cadmium and sulfur both in octadecane solutions at 230-240 °C. These structures showed high PL quantum yields (20-40%), relatively narrow emission bands, and tunable emission colors from about 520 to 650 nm depending on the number of CdSe monolayers. 

The wide tunability of the laser emission and the very high gain are the two most prominent features of dye lasers that are not found in other lasers (with the exception, perhaps, of semiconductor lasers which, however, only reach peak powers that are many orders of magnitude lower than those of dye lasers). 

The remarkable phosphorescence properties of Ir(III)-cyclometalated species (high luminescence quantum yield and long lifetimes, tunable emission peak), prove of use in several areas in addition to OLED application. We only mention here a few representative examples regarding the Ir(CAN)2(NAN)+ chromophores in (a)-(c) below. For these complexes as incorporated in suitable materials, the emission is expected of Ir -(NAN) CT nature and the alteration of their luminescence features can be associated to other useful properties of the substrates. 

Wtirthner, F., Ahmed, S., Thalacker, C. and Debaerdemaeker, T. (2002) Core-substituted naphthalene bisimides New fluorophores with tunable emission wavelength for FRET studies. Chemistry-A European Journal, 8, 4742-50. 

Fig. 5 Tunable emission of K[AuT(CN)2] solutions by controlling the concentration, excitation wavelength, solvent, and temperature. From [35]...

Copolymers containing alternating l,4-bis(phenylethenyl)benzene, l,4-bis(phenylethenyl)-2,5-dimethoxybenzene or l,5-bis(phenylethenyl)naphthalene chromophores, and dibenzo-24-crown-8 spacers within the polymer backbone, best represented by 87, showed blue light emission in solution, and tunable photoluminescence and electroluminescence depending on the structure of the chromophore. Blends of these copolymers with a small amount of poly(ethylene oxide), and lithium salt as active layers, form efficient light-emitting electrochemical cells <2003JMC800>. 

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