Efficient electron transporting blue emitting materials obtained from excimer emission assisted by thermally activated delayed fluorescence.

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†Electronic Supplementary Information (ESI) available: X-ray crystallographic data in CIF format for the complexes Ir2 and Ir4 [CCDC 973778 (Ir2) and 1005716 (Ir4)], NMR and MASS spectra of ligands and complexes, TGA−DSC thermal curves, cyclic voltammograms, lifetime curves, selected bond lengths and angles, intermolecular interactions, calculated transitions of Ir1-Ir5 in CH2Cl2 media and composition of the MOs and the assignment of different fragments. CIF files. See Herein, we have synthesized a series of 2',6'-difluoro-2,3'-bipyridine cyclometalating ligands by substituting electronwithdrawing (-CHO, -CF3, -CN) and electron-donating (-OMe, -NMe2) groups at the 4′ posiƟon of the pyridyl moiety and utilized for the construction of five new iridium(III) complexes (Ir1-Ir5) in the presence of picolinate as an ancillary ligand. The photophysical properties of the developed iridium(III) compounds were investigated with a view to understand the substituent effects. The strong electron-withdrawing (-CN) group containing iridium(III) compound (Ir3) exhibits highly efficient genuine green phosphorescence (λmax= 508 nm) at room temperature in solution and in thin film, with an excellent quantum efficiency (ΦPL) of 0.90 and 0.98, respectively. On the other hand, the -CF3 group substituted iridium(III) compound (Ir2) displays a sky-blue emission (λmax = 468 nm) with a promising quantum efficiency (ΦPL = 0.88 and 0.84 in solution and in thin film, respectively). The -CHO substituted iridium(III) complex (Ir1) showed greenishyellow emission (λmax = 542 nm). Most importantly, the strong electron-donating -NMe2 substituted iridium(III) complex (Ir5) gives a structureless and a broad emission profile in the wavelength region 450 to 700 nm (λmax = 520 nm) with a poor quantum efficiency. An intense blue phosphorescence with impressive quantum efficiency, especially in thin-film noted in the case of -OMe substituted iridium(III) complex (Ir4). Comprehensive density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches have been performed on the ground and excited states of the synthesized iridium(III) complexes, in order to obtain information about the absorption and emission processes and to gain deeper insights into the photophysical properties. The combinations of a smaller ΔES1-T1 and higher contribution of 3 MLCT in the emission process result in the higher quantum yields and lifetime values for complexes Ir1-Ir3. Multi-layered Phosphorescence Organic Light Emitting Diodes (PhOLEDS) were designed using the phosphorescent dopants Ir2, Ir3 and Ir4 and evaluated their elecroluminescence properties. The compound Ir4 at a doping level of 5 wt% shows the best performance with an external quantum efficiency of 4.7% , in nonoptimized device, and power efficiency of 5.8 lm W −1 , together with a true-blue chromacity CIEx,y = 0.15, 0.17 recorded at maximum brightness of 33,180 cd/m 2 . 28,[45][46][47][48][49][50][51] Accordingly, several groups have demonstrated that phosphorescence emission wavelengths can be tuned in t...

Two new porphyrin arrays-a hexamer and a nonamer-have been synthesized and characterized by elemental analysis as well as mass, (1)H NMR, and UV-vis spectroscopic methods. The scheme of construction of these arrays employs a synthetic protocol involving sequential "organic" and "inorganic" reactions conducted, respectively, at the peripheral meso-phenyl ring and the central tin(IV) ion of the porphyrin scaffold. The architecture of the hexamer is such that it is based on a covalently linked tin(IV) porphyrin dimer, with each of the two tin(IV) centers trans-axially ligated to two free-base porphyrins, while the higher homologue features a tin(IV) porphyrin trimer as the basal unit, with its central metalloid ions having two free-base porphyrins as axial ligands. This extended, "axial-bonding"-type architecture of the new arrays has been investigated by the (1)H NMR method, which reveals characteristic ring-current-induced shifts and coupling patterns for the resonances due to protons of the axial free-base porphyrin subunits. The presence of any ring-ring (basal-basal, basal-axial, or axial-axial) interaction in these arrays is not obvious from their UV-vis and redox potential data, which are close to those of the corresponding constituent monomeric species. On the other hand, their singlet-state activities are quite different from those of the precursor reference compounds as probed by steady-state fluorescence. The results of the detailed investigations carried out on these hybrid, "bichromophoric" arrays have been interpreted in terms of the occurrence of intraarray, interchromophore energy- and electron-transfer reactions.

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“Equatorial” energy transfer: Orientation control of intramolecular energy transfer (EnT) is found in the donor–acceptor system shown, light absorbed by the “peripheral” anthracene is efficiently transferred to the porphyrin, but that by the “axial” anthracene subunits is not.

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