Two-photon absorption properties of simple neutral Ir(III) complexes

A series of neutral Ir(2-phenylpyridine)3 derivatives substituted on the para-position of the pyridyl ligands with a π-conjugated substituent possessing different donor abilities has been prepared. Their two-photon absorption properties have been determined using the Z-scan technique. Such simple iridium(III) neutral complexes, which are easy to synthesize, show good two-photon absorption activity, with relevant TPA cross sections (the best is 750 GM), giving rise to multifunctional chromophores, since they present also high second-order NLO properties.

Heteroleptic cationic iridium(iii) complexes bearing phenanthroline derivatives with extended π-conjugation as potential broadband reverse saturable absorbers

Fluorenyl substitution at the diimine ligand broadened the excited-state absorption to near-IR, and enhanced reverse saturable absorption at 532 nm for the cationic Ir(iii) complexes.

Stabilization of a Cyclometalated Ruthenium Sensitizer on Nanocrystalline TiO2 by an Electrodeposited Covalent Layer

A cyclometalated ruthenium sensitizer 3 containing a triphenylamine unit was synthesized and immobilized on a nanocrystalline TiO₂ surface. By using oxidative electrochemical deposition, a covalent layer of a related cyclometalated ruthenium complex 2 was coupled to the top of dye 3. Electrochemical studies suggested that complex 2 was immobilized on the TiO₂/3 film surface by a tetraphenylbenzidine linker to form a dimer-like structure. The immobilization of 3 and 2 was further supported by absorption spectral analysis. The resulting electrodeposited TiO₂/(3+2) film displays significantly enhanced sensitizer stabilization toward basic aqueous NaOH solution with respect to the original TiO₂/3 film. The dye-sensitized solar cells with the TiO₂/(3+2) photoanode display a power conversion efficiency of 4.4%, which is slightly inferior to that with the TiO₂/3 film (5.1%) under the same measurement conditions.

Multifunctional Cationic Iridium(III) Complexes Bearing 2-Aryloxazolo[4,5-f][1,10]phenanthroline (N^N) Ligand: Synthesis, Crystal Structure, Photophysics, Mechanochromic/Vapochromic Effects, and Reverse Saturable Absorption

A series of 2-aryloxazolo[4,5-f][1,10]phenanthroline ligands (N^N ligands) and their cationic iridium(III) complexes (1-11, aryl = 4-NO₂-phenyl (1), 4-Br-phenyl (2), Ph (3), 4-NPh₂-phenyl (4), 4-NH₂-phenyl (5), pyridin-4-yl (6), naphthalen-1-yl (7), naphthalen-2-yl (8), phenanthren-9-yl (9), anthracen-9-yl (10), and pyren-1-yl (11)) were synthesized and characterized. By introducing different electron-donating or electron-withdrawing substituents at the 4-position of the 2-phenyl ring (1-5), or different aromatic substituents with varied degrees of π-conjugation (6-11) on oxazolo[4,5-f][1,10]phenanthroline ligand, we aim to understand the effects of terminal substituents at the N^N ligands on the photophysics of cationic Ir(III) complexes using both spectroscopic methods and quantum chemistry calculations. Complexes with the 4-R-phenyl substituents adopted an almost coplanar structure with the oxazolo[4,5-f][1,10]phenanthroline motif, while the polycyclic aryl substituents (except for naphthalen-2-yl) were twisted away from the oxazolo[4,5-f][1,10]phenanthroline motif. All complexes possessed strong absorption bands below 350 nm that emanated from the ligand-localized ¹π,π*/¹ILCT (intraligand charge transfer) transitions, mixed with ¹LLCT (ligand-to-ligand charge transfer)/¹MLCT (metal-to-ligand charge transfer) transitions. At the range of 350-570 nm, all complexes exhibited moderately strong ¹ILCT/¹LLCT/¹MLCT transitions at 350-450 nm, and broad but very weak ³LLCT/³MLCT absorption at 450-570 nm. Most of the complexes demonstrated moderate to strong room temperature phosphorescence both in solution and in the solid state. Among them, complex 7 also manifested a drastic mechanochromic and vapochromic luminescence effect. Except for complexes 1 and 4 that contain NO₂ or NPh₂ substituent at the phenyl ring, respectively, all other complexes exhibited moderate to strong triplet excited-state absorption in the spectral region of 440-750 nm. Moderate to very strong reverse saturable absorption (RSA) of these complexes appeared at 532 nm for 4.1 ns laser pulses. The RSA strength followed the trend of 7 > 11 > 9 > 3 > 2 ≈ 4 > 5 ≈ 10 ≈ 6 ≈ 8 > 1. The photophysical studies revealed that the different 2-aryl substituents on the oxazole ring impacted the singlet and triplet excited-state characteristics dramatically, which in turn notably influenced the RSA of these complexes.

Iridium-Based High-Sensitivity Oxygen Sensors and Photosensitizers with Ultralong Triplet Lifetimes

The photophysics of a series of bichromophoric molecules featuring an intramolecular triplet energy transfer between a triscyclometalated iridium(III) complex and covalently linked organic group are studied. By systematically varying the energy gap (0.1-0.3 eV) between the donor (metal complex) and acceptor (pyrene unit), reversible triplet energy transfer processes with equilibrium constant K ranging from ca. 500 to 40 000 are established. Unique photophysical consequences of such large K values are observed. Because of the highly imbalanced forward and backward energy transfer rates, triplet excitons dominantly populate the acceptor moiety in the steady state, giving rise to ultralong luminescence lifetimes up to 1-4 ms. Because the triscyclometalated Ir and triplet pyrene groups both impart relatively small nonradiative energy loss, decent phosphorescence quantum yields (Φ = 0.1-0.6) are attained in spite of the exceptionally prolonged excited states. By virtue of such precious combination of long-lived triplet state and high Φ, these bichromophoric molecules can serve as highly sensitive luminescent sensors for detecting trace amount of O2 and as potent photosensitizers for producing singlet oxygen even under low-oxygen content conditions.

A singlet oxygen photosensitizer enables photoluminescent monitoring of singlet oxygen doses

Dichromophoric molecular dyad enables photosensitization and detection of sinlget oxygen.

Conjugated Polymer Nanoparticle-Triplet Emitter Hybrids in Aqueous Dispersion: Fabrication and Fluorescence Quenching Behavior

Conjugated polymer nanoparticles based on poly[9,9-bis(2-ethylhexyl)fluorene] and poly[N-(2,4,6-trimethylphenyl)-N,N-diphenylamine)-4,4'-diyl] are fabricated using anionic surfactant sodium dodecylsulphate in water by miniemulsion technique. Average diameters of polyfluorene and polytriarylamine nanoparticles range from 70 to 100 and 100 to 140 nm, respectively. The surface of the nanoparticles is decorated with triplet emitting dye, tris(2,2'-bipyridyl)ruthenium(II) chloride. Intriguing photophysics of aqueous dispersions of these hybrid nanoparticles is investigated. Nearly 50% quenching of fluorescence is observed in the case of dye-coated polyfluorene nanoparticles; excitation energy transfer is found to be the dominant quenching mechanism. On the other hand, nearly complete quenching of emission is noticed in polytriarylamine nanoparticle-dye hybrids. It is proposed that the excited state electron transfer from the electron-rich polytriarylamine donor polymer to Ru complex leads to the complete quenching of emission of polytriarylamine nanoparticles. The current study offers promising avenues for developing aqueous solution processed-electroluminescent devices involving a conjugated polymer nanoparticle host and Ru or Ir-based triplet emitting dye as the guest.

A cyclometallated fluorenyl Ir(iii) complex as a potential sensitiser for two-photon excited photodynamic therapy (2PE-PDT)

A cyclometallated fluorenyl Ir(iii) complex that exhibits enhanced triplet oxygen sensing properties for two photon photodynamic therapy is reported.