Singlet emitters

The simplest multilayer OLED consists of two organic layers (Fig. 11.6), one EML which is at the same time an ETL (e.g. Alq3), and an HTL (e.g. NPB). )Alq3 is a singlet emitter. The layer thicknesses can be optimised so that the electron and hole currents are equal and that the recombination and thus the emission occur in the Alq3, and there in a thin layer near the interface to the HTL This allows the... 

The terpyridine-substituted difluoroborondipyrromethene dye 88 is a singlet emitter at 540 nm (18 500 cm ) and its triplet state emission extends from 550-750 nm (18200-13 300 cm ), which makes it a potential sensitizer of lanthanide NIR luminescence. In [Yb(N03)3(88)] (see fig. 75), the lanthanide ion is bound to the terdentate terpyridine and to three bidentate nitrate counterions, in a distorted tricapped antiprismatic geometry. The Ln complexes (Ln = La, Nd, Er, Yb) have large absorption coefficients (65 000 cm ... 

Subsequent studies (63,64) suggested that the nature of the chemical activation process was a one-electron oxidation of the fluorescer by (27) followed by decomposition of the dioxetanedione radical anion to a carbon dioxide radical anion. Back electron transfer to the radical cation of the fluorescer produced the excited state which emitted the luminescence characteristic of the fluorescent state of the emitter. The chemical activation mechanism was patterned after the CIEEL mechanism proposed for dioxetanones and dioxetanes discussed earher (65). Additional support for the CIEEL mechanism, was furnished by demonstration (66) that a linear correlation existed between the singlet excitation energy of the fluorescer and the chemiluminescence intensity which had been shown earher with dimethyl dioxetanone (67). 

SMOLEDs contain small-molecule emissive materials that can be processed by either vacuum deposition (evaporative) techniques or solution coating. The emissive small molecule may be a fluorescent (singlet excited state) or a phosphorescent (triplet excited state) emitter. 

Phenylquinoxalines (30) turned out to be both fluorescent and phosphorescent emitters [167, 168]. By using these molecules as host, singlet excitons as well as triplet excitons can be transfered by long-range interactions to phosphorescent dopant molecules such as 66. 

Lipid hydroperoxides are also generated in singlet molecular oxygen mediated oxidations and by the action of enzymes such as lipoxygenases and cyclooxygenases. Chemiluminescence (CL) arising from lipid peroxidation has been used as a sensitive detector of oxidative stress both in vitro and in vivo . Several authors have attributed ultra-weak CL associated with lipid peroxidation to the radiative deactivation of O2 and to triplet-excited carbonyls (63, 72) (equations 35 and 36) " . It has been proposed that the latter emitters arise from the thermolysis of dioxetane intermediates (61, 62) (equation 35), endoperoxide (73) (equation 37) and annihilation of aUtoxyl, as well as peroxyl radicals ... 

The phenomenal increase in excited-singlet-state acidity of aromatic hydroxy compounds makes them good excited-state proton emitters, with deprotonation... 

Regarding the latter issue, it has to be noticed that for the phosphorescence decay of isolated ligands, the values for rr may be in the ms to sec time range or longer [16]. For the complexes, the heavy atom effect may cause singlet-triplet mixing to an extent that a formal 3LC level exhibits tr as short as tenths of xs [1]. Consistent with this, we shall see later that radiative lifetimes for 3LC emitters of the Ir(III)-polyimine family are tr 50 xs or larger (kt 0.2 x 105 s-1 or smaller, Eq. 2). 

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