Diego Rota Martir

Enhancing the photoluminescence quantum yields of blue-emitting cationic iridium(III) complexes bearing bisphosphine ligands

Herein we present a structure–property relationship study of thirteen cationic iridium(III) complexes of the form of [Ir(C^N)2(P^P)]PF6 in both solution and the solid state through systematic evaluation of six bisphosphine (P^P) ligands (xantphos, dpephos, dppe, Dppe, nixantphos and isopropxantphos). All of the complexes are sky-blue emissive, but their photoluminescence quantum yields (ΦPL) are generally low. However, strong and long-lived blue luminescence (λem = 471 nm; ΦPL = 52%; τe = 13.5 μs) can be obtained by combining the reduced bite angle of the 1,2-bis-diphenylphosphinoethene (dppe) chelate with the bulky 2-(4,6-difluorophenyl)-4-mesitylpyridinato (dFmesppy) cyclometalating ligand. To the best of our knowledge this is the highest ΦPL and the longest τe reported for cyclometalated iridium(III) complexes bearing bisphosphine ligands. Light-emitting electrochemical cells (LEECs) were fabricated using lead complexes from this study, however due in part to the irreversible electrochemistry, no functional LEEC was achieved. Organic light-emitting diodes were successfully fabricated but only attained maximum external quantum efficiencies of 0.25%.

Homochiral Emissive Λ8- and Δ8-[Ir8Pd4]16+ Supramolecular Cages

Abstract Synthetic self‐assembly is a powerful technique for the bottom‐up construction of discrete and well‐defined polyhedral nanostructures resembling the spherical shape of large biological systems. In recent years, numerous Archimedean‐shaped coordination cages have been reported based on the assembly of bent monodentate organic ligands containing two or more distal pyridyl rings and square‐planar PdII ions. The formation of photoactive PdII metallamacrocycles and cages, however, remain rare. Here we report the first examples of emissive and homochiral supramolecular cages of the form [Ir8Pd4]16+. These cages provide a suitably sized cavity to host large guest molecules. Importantly, encapsulation and energy transfer have been observed between the blue‐emitting NBu4[Ir(dFppy)2(CN)2] guest and the red‐emitting Δ8‐[Ir8Pd4]16+ cage.

Homochiral Self-Sorted and Emissive IrIII Metallo-Cryptophanes

Abstract The racemic ligands (±)‐tris(isonicotinoyl)‐cyclotriguaiacylene (L1), or (±)‐tris(4‐pyridyl‐methyl)‐cyclotriguaiacylene (L2) assemble with racemic (Λ,Δ)‐[Ir(ppy)2(MeCN)2]+, in which ppy=2‐phenylpyridinato, to form [{Ir(ppy)2}3(L)2]3+ metallo‐cryptophane cages. The crystal structure of [{Ir(ppy)2}3(L1)2]⋅3BF4 has MM‐ΛΛΛ and PP‐ΔΔΔ isomers, and homochiral self‐sorting occurs in solution, a process accelerated by a chiral guest. Self‐recognition between L1 and L2 within cages does not occur, and cages show very slow ligand exchange. Both cages are phosphorescent, with [{Ir(ppy)2}3(L2)2]3+ having enhanced and blue‐shifted emission when compared with [{Ir(ppy)2}3(L1)2]3+.

Multimetallic and mixed environment iridium(III) complexes : a modular approach to luminescence tuning using a host platform

Abstract Mononuclear and trinuclear bis‐cyclometallated IrIII complexes of the host ligands tris(4‐[4′‐methyl‐2,2′‐bipyridyl]methyl)cyclotriguaiacylene (L1) and tris(4‐(4′‐methyl‐2,2′‐ bipyridyl)carboxy)cyclotriguaiacylene (L2) have been prepared. Complexes [{Ir(ppy)2}3(L1)](PF6)3 (1.1), [{Ir(ppy)2}(L1)](PF6)3 (1.2), [{Ir(ppy)2}3(L2)](PF6)3 (2.1) and [{Ir(ppy)2}(L2)](PF6)3 (2.2) (where ppy=phenylpyridinato) showed distinct photophysical properties depending on the L ligand. Complexes featuring the L1 ligand were comparatively blue‐shifted in solution, with longer lifetimes and higher quantum yields. The mixed bis‐cyclometallated IrIII complexes [{Ir(ppy)2}{Ir(dFppy)2}2(L1)](PF6)3 (1.3), [{Ir(ppy)2}{Ir(dFppy)2}2(L2)](PF6)3 (2.3), [{Ir(ppy)2}2{Ir(dFppy)2}(L1)](PF6)3 (1.4) and [{Ir(ppy)2}2{Ir(dFppy)2}(L2)](PF6)3 (2.4) (where dFppy=2,4‐difluorophenylpyrinato) were also synthesised. Steady‐state and time‐resolved spectroscopy, along with electrochemical investigations, show that the Ir(III) chromophores within these mixed Ir‐environment species behave as isolated centres, with no energy transfer or electronic communication between them.

Pyridine-functionalized carbazole donor and benzophenone acceptor design for thermally activated delayed fluorescence emitters in blue organic light-emitting diodes

Abstract. We report a molecular design approach for blue-emitting thermally activated delayed fluorescence (TADF) molecules. The two TADF emitters, (4-(3,6-di(pyridin-3-yl)-9H-carbazol-9-yl)phenyl)(phenyl)methanone (3PyCzBP) and (4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl)(phenyl)methanone (4PyCzBP), possess a pyridine-functionalized carbazole donor and a benzophenone acceptor. Both compounds show broad charge-transfer emission in dichloromethane with a λmax at 497 nm and a photoluminescence quantum yield, ϕPL, of 56% for 3PyCzBP and a λmax at 477 nm and a ϕPL of 52% for 4PyCzBP. The ϕPL decreased to 18% and 10%, respectively, for 3PyCzBP and 4PyCzBP in the presence of O2 confirming that triplet states involved in emission. The poly(methyl methacrylate) (PMMA)-doped (10 wt. %) films show blueshifted emission with λmax at 450 and 449 nm for 3PyCzBP and 4PyCzBP, respectively. The maximum ϕPL of 23.4% is achieved for these compounds in PMMA-doped film. The difference in energy between the singlet and triplet excited states (ΔEST) is very small at 0.06 and 0.07 eV for 3PyCzBP and 4PyCzBP, respectively. Multilayer organic light-emitting diode devices fabricated using these molecules as emitters show that the maximum efficiency (EQEmax) of the blue devices is 5.0%.

Tuning the optical properties of silicon quantum dots via surface functionalization with conjugated aromatic fluorophores

Silicon Quantum Dots (SQDs) have recently attracted great interest due to their excellent optical properties, low cytotoxicity, and ease of surface modification. The size of SQDs and type of ligand on their surface has a great influence on their optical properties which is still poorly understood. Here we report the synthesis and spectroscopic studies of three families of unreported SQDs functionalized by covalently linking to the aromatic fluorophores, 9-vinylphenanthrene, 1-vinylpyrene, and 3-vinylperylene. The results showed that the prepared functionalized SQDs had a highly-controlled diameter by HR-TEM, ranging from 1.7–2.1 nm. The photophysical measurements of the assemblies provided clear evidence for efficient energy transfer from the fluorophore to the SQD core. Fӧrster energy transfer is the likely mechanism in these assemblies. As a result of the photogenerated energy transfer process, the emission color of the SQD core could be efficiently tuned and its emission quantum efficiency enhanced. To demonstrate the potential application of the synthesized SQDs for bioimaging of cancer cells, the water-soluble perylene- and pyrene-capped SQDs were examined for fluorescent imaging of HeLa cells. The SQDs were shown to be of low cytotoxicity

Influencing the Optoelectronic Properties of a Heteroleptic Iridium Complex by Second-Sphere H-Bonding Interactions

The use of a new second-sphere coordination methodology for emission color tuning of iridium complexes is presented. We demonstrate that a complementary H-bonding guest molecule binding through contiguous triple H-bonding interactions can induce a shift in the emission of the iridium complex from green to blue without the need to alter the ligand structure around the metal center, while simultaneously increasing the photoluminescence quantum yield in solution. The association constant for this host-guest interaction was determined to be Ka = 4.3 × 103 M-1 in a solution of 2% dimethyl sulfoxide in chloroform by UV-vis titration analysis and the impact of the hydrogen bonding interaction further probed by photoluminescence, electrochemical, and computational methods. Our findings suggest that directed self-assemblies are an effective approach to influencing emission properties of phosphorescent iridium(III) complexes.

CCDC 1490702: Experimental Crystal Structure Determination

Related Article: Diego Rota Martir, Cristina Momblona, Antonio Pertegas, David B. Cordes, Alexandra M. Z. Slawin, Henk J. Bolink, and Eli Zysman-Colman|2016|ACS Applied Materials and Interfaces|8|33907|doi:10.1021/acsami.6b14050