Probe exciplex structure of highly efficient thermally activated delayed fluorescence organic light emitting diodes.

The lack of structural information impeded the access of efficient luminescence for the exciplex type thermally activated delayed fluorescence (TADF). We report here the pump-probe Step-Scan Fourier transform infrared spectra of exciplex composed of a carbazole-based electron donor (CN-Cz2) and 1,3,5-triazine-based electron acceptor (PO-T2T) codeposited as the solid film that gives intermolecular charge transfer (CT), TADF, and record-high exciplex type cyan organic light emitting diodes (external quantum efficiency: 16%). The transient infrared spectral assignment to the CT state is unambiguous due to its distinction from the local excited state of either the donor or the acceptor chromophore. Importantly, a broad absorption band centered at ~2060 cm-1 was observed and assigned to a polaron-pair absorption. Time-resolved kinetics lead us to conclude that CT excited states relax to a ground-state intermediate with a time constant of ~3 µs, followed by a structural relaxation to the original CN-Cz2:PO-T2T configuration within ~14 µs.

Sky Blue-Emitting Iridium(III) Complexes Bearing Nonplanar Tetradentate Chromophore and Bidentate Ancillary.

Tetradentate chelates bearing tripodal arranged terpyridine and a functional pyrazole unit (i.e., L1-H and L2-H) were employed in preparation of Ir(III) complexes [Ir(L1)Cl2] (1) and [Ir(L2)Cl2] (2); subsequent chloride-to-bipyrazolate substitution gave [Ir(L1)(bipz)] (3) and [Ir(L2)(bipz)] (4). Single-crystal X-ray structural studies on 1 and 3 showed the possession of a tetradentate chelate, whereas the remaining cis-sites are occupied by either dual chlorides or the bipz chelate, respectively. Sky blue organic light-emitting diode with peak efficiencies (10.1%, 19.8 cd·A-1, and 20.4 lm·W-1) was successfully fabricated using 3 (or 4) as dopant emitter, highlighting the potential application of this class of Ir(III) phosphor.

Tetragold(I) complexes: solution isomerization and tunable solid-state luminescence.

In this study, a new family of tetranuclear gold(I) triphosphine derivatives bearing alkynyl and thiolate groups have been efficiently synthesized by treating the polymeric acetylides (AuC2R)n or a thiolate (AuSPh)n sequentially with the (a) phosphine ligand and (b) cationic complex [Au3(P^P^P)2](3+) (P^P^P = PPh2CH2PPhCH2PPh2). The clusters [Au4(P^P^P)2(C2R)2](2+) [R = Ph (1), biphenyl (2), terphenyl (3), C6H4OMe (4), C6H4NMe2 (5), C6H11O (6), and C6H4CF3 (7)] and [Au4(P^P^P)2(SPh)2](2+) (8) were characterized by X-ray crystallography in the solid state. NMR spectroscopic investigations in solution revealed that the majority of alkynyl clusters 1-7 exist as two isomeric species in slow chemical equilibria. All complexes 1-8 exhibit moderate-to-strong photoemission in the solid state with quantum yields from 0.07 to 0.51. The luminescence behavior was rationalized using quantum chemical density functional theory methods. The high emission efficiency of these tetragold(I) compounds and their good stability in film allowed for the fabrication of an organic electroluminescent device (OLED). Employing complex 5 (Φ = 0.51), an OLED was fabricated under a solution process to give a good external quantum efficiency of 3.1%, corresponding to a current efficiency of 6.1 cd/A and a power efficiency of 5.3 lm/W, with Commission Internationale de I'Eclairage coordinates of (0.52, 0.46).