Green emission

Not only the absorption behaviour, but also all the physical properties of derivatives (32) are related to the nature of the 2,5-substitution pattern. For example, a blue-green emission is observed for di(2-pyridyl)phosphole (32b) whereas the emission of di(2-thienyl)phosphole (32a) is red-shifted (AAj,nj= 35 nm) [36]. Likewise, cyclic voltammetry (CV) revealed that derivative (32a), featuring electron-rich thienyl substituents, is more easily oxidised than compound (32b), which possesses electron-deficient pyridyl substituents [36]. 

It has been suggested that Cd vacancies are responsible for this green emission assuming that adsorbed is able to create such vacancies. Doping the colloid... 

P-36 ZnCdS2 Ag.Ni ZnS, CdS, (Zno.7i5.Ago.285)S2, (Zn0933.Ni0.067)S2, MgCl2, NaCl, BaCl2 Fast decay screens for display. Yellow-green emission at 532 nm... 

Long decay time phosphor for use in radar applications. Green emission at 525 nmAs3+ added to promote longer decay... 

MgW04 W 3MgC03.Mg(0H)2-3H20, W03 Blue-green emission used in white blends for fluorescent lamps... 

Experiment 5. The fluorescence of crystalline allelochemicals and some pigments Yellow-green emission is peculiar to quercetin, while orange - to rutin. Azulene fluoresce in blue, carotenoids - in yellow, and chlorophyll - in red. 

One of the more efficient CL substances, lucigenin (10,10 -dimethyl-9,9 -biscridinium nitrate), was discovered by Gleu and Petsch in 1935 (Fig. 5). They observed an intense green emission when lucigenin was oxidized in an alkaline medium [72], Other acridinium derivatives were shown to produce CL emission upon hydrogen peroxide oxidation of aqueous alkaline solutions. The main reaction product was /V-mcthylacridone, acting as an active intermediate in the mechanism proposed by Rauhut et al. [73, 74] (Fig. 6). 

The related copolymer 94, synthesized in the 1980s by Feast et al. [144], presents a rare example of a PPV-containing phenyl substituents on the vinylene unit. Apparently, the steric hindrance caused by phenyl substituents in 94 is not dramatic, and the optical properties of 94 are similar to those of other PPVs (green emission, APL AEL 530 nm). An internal QE of up to 1% was reported with multilayer 94-based PLEDs containing PPV 1 and PVK as HTL [145]. 

More recently, it was shown by List et al. [293-296] and later by Moses et al. [246] that the green emission of the PFs is due to fluoren-9-one defects in the polymer chain. This was confirmed by comparison of PL films annealed in an inert atmosphere and in air a progressive additional band in the green region was observed on annealing in air (Figure 2.12) [246],... 

Many studies on side-chain modifications in PF were initially based on the idea of excimer formation, resulting in the green emission during LED operation or in solid-state PL on annealing PF films. This resulted in several proposed strategies for the design of fluorene side-chain homopolymers, where bulky substituents at position 9 of the fluorene moiety should sterically prevent (hinder) interchain interaction and thus improve the stability of blue emission. 

Fujiki and coworkers [290] synthesized asymmetrically substituted PFs, bearing a bulky Frechet-type dendron and a less bulky 3,6-dioxaoctyl group in position 9. The polymers 215-217 showed a pure blue PL emission with rather low green emission band (at 520 nm) for the films annealed at 200°C for 3 h (in vacuum) (Chart 2.51). 

Another example of spiro-derivatized PF was demonstrated by Bo and coworkers [319], who synthesized soluble spiro-bifluorene-based polymer 219. This polymer showed stable bright-blue PL (d>PL = 91% in toluene), and showed no green emission in the annealed film (although no device preparation has been reported as yet) (Chart 2.52). 

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