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.

Introduction of a triphenylamine substituent on pyridyl rings as a springboard for a new appealing brightly luminescent 1,3-di-(2-pyridyl)benzene platinum(II) complex family.

The preparation and characterization of three new complexes, namely [Pt(1,3-bis(4-triphenylamine-pyridin-2-yl)-4,6-difluoro-benzene)Cl] ([PtL1Cl]), [Pt(1,3-bis(4-triphenylamine-pyridin-2-yl)-5-triphenylamine-benzene)Cl] ([PtL2Cl]), and [Pt(1,3-bis(4-triphenylamine-pyridin-2-yl)-5-mesityl-benzene)Cl] ([PtL3Cl]), is reported. All of them are highly luminescent in dilute deaerated dichloromethane solution (Φlum = 0.88-0.90, in the yellow-green region; the λmax,em in nm for the monomers are: 562, 561 and 549 for [PtL1Cl], [PtL2Cl] and [PtL3Cl], respectively).[PtL1Cl] is the most appealing, being characterized by a very long lifetime (103.9 µs) and displaying intense NIR emission in concentrated deaerated solution (Φlum = 0.66) with essentially no "contamination" by visible light < 600 nm. This complex allows the fabrication of both yellow-green and deep red/NIR OLEDs; OLED emissions are in the yellow-green (CIE = 0.38, 0.56) and deep red/NIR (CIE = 0.65, 0,34) regions, for [PtL1Cl] 8 wt% (with 11% ph/e EQE) and pure [PtL1Cl] (with 4.3% ph/e EQE), respectively.

The switchable phosphorescence and delayed fluorescence of a new rhodamine-like dye through allenylidene formation in a cyclometallated platinum(ii) system.

A new rhodamine-like alkyne-substituted ligand (Rhodyne) was designed to coordinate a cyclometallated platinum(ii) system. The chemo-induced "ON-OFF" switching capabilities on the spirolactone ring of the Rhodyne ligand with an end-capping platinum(ii) metal centre can modulate the interesting acetylide-allenylidene resonance. The long-lived 3IL excited state of Rhodyne in its ON state as an optically active opened form was revealed via steady-state and time-resolved spectroscopy studies. Exceptional near-infrared (NIR) phosphorescence and delayed fluorescence based on a rhodamine-like structure were observed at room temperature for the first time. The position of the alkyne communication bridge attached to the platinum(ii) unit was found to vary the lead(ii)-ion binding mode and also the possible resonance structure for metal-mediated allenylidene formation. The formation of a proposed allenylidene resonance structure was suggested to rationalize these phenomena.

Palladium-Catalyzed C-H Bond Arylation of Cyclometalated Difluorinated 2-Arylisoquinolinyl Iridium(III) Complexes.

The utility of C-H bond functionalization of metalated ligands for the elaboration of aryl-functionalized difluorinated-1-arylisoquinolinyl Ir(III) complexes has been explored. Bis[(3,5-difluorophenyl)isoquinolinyl](2,2,6,6-tetramethyl-3,5-heptanedionato) iridium(III) undergoes Pd-catalyzed C-H bond arylation with aryl bromides. The reaction regioselectively occurred at the C-H bond flanked by the two fluorine atoms of the difluoroaryl unit, and on both cyclometalated ligands. This post-functionalization gives a straightforward access to modified complexes in only one manipulation and allows to introduce thermally sensitive functional groups, such as trifluoromethyl, nitrile, benzoyl, or ester. The X-ray crystallography, photophysical, and electrochemical properties of the diarylated complexes were investigated. Whatever the nature of the incorporated substituted aryl groups is, all obtained complexes emit red phosphorescence (622-632 nm) with similar lifetimes (1.9-2 µs).

Exploiting the Reactivity of Fluorinated 2-Arylpyridines in Pd-Catalyzed C-H Bond Arylation for the Preparation of Bright Emitting Iridium(III) Complexes.

Pd-catalyzed C-H bond arylation applied to 2-(2,4-difluorophenyl)-5-(trifluoromethyl)pyridine (1) and 2-(3,5-difluorophenyl)-5-(trifluoromethyl)pyridine (5) allows the access to two families of Ir(III) complexes, charge-neutral and cationic species. The reaction is regioselective since only the C3- or C4-position of the fluorinated phenyl ring of 1 or 5 is readily functionalized - namely the C-H bond flanked by the two fluorine atoms which is the most acidic - which allows the electronic control of the reactive site. A range of electron-withdrawing (CN, CO2Et, C(O)Me) substituents on the aryl group has been incorporated leading to the pro-ligands (1, Ar-2,4-dFppy; 2, Ar = p-C6H4-CN; 3, Ar = p-C6H4-CO2Et; 4, Ar = p-C6H4-C(O)Me; 5, and Ar-3,5-dFppy; 6, Ar = p-C6H4-CO2Et). The unsubstituted complexes F1/G1 and F1/G5 featuring 1 and 5, respectively, as C^N ligands are used as reference complexes. The families of five charge-neutral [Ir(C^N)2(N^O)] complexes (C^N is 2-(5-aryl-(4,6-difluorophenyl)-5-(trifluoromethyl)pyridinato (F2-F4), and 2-(4-aryl-(3,5-difluorophenyl)-5-(trifluoromethyl)pyridinato (F5-F6), N^O = 2-picolinate) and five cationic [Ir(C^N)2(N^N)]PF6 complexes (N^N = dmbpy is 4,4'-dimethyl-2,2'-bipyridine) (G2-G6) were synthesized, and their structural and photophysical properties were studied with comparison to the unsubstituted analogues used as reference complexes. The appended aryl group provides large steric bulk as the biaryl fragment is twisted as shown by the X-ray crystal structures of F2, F5, F6, G3, and G5. These latter complexes display a wide variety of different Ir···Ir intermetallic distances in crystals, from 8.150 Å up to 15.034 Å. Moreover, the impact on the emission energy is negligible, as a result of the breaking of the conjugation between the two aryl groups. Charge-neutral complexes [Ir(C^N)2(N^O)] (N^O = 2-picolinate) show bright luminescence: F2-F4 (λem = 495-499 nm) are blue-green emitters, whereas F5 and F6 (λem = 537, 544 nm), where the fluorine substituents are located at the C3- and C5-positions, emit in the green region of the visible spectrum. In all cases, a unitary photoluminescence quantum yield is found. The improvement of Φ might be explained by an increase of the radiative rate constant due to a higher degree of rigidity of these congested molecules, compared to the unsubstituted complex F1. The same trends are observed for the family of complexes G. Complexes G1-G4 exhibit blue photoluminescence, and G5 and G6 lead to a red-shifted emission band, as also found for the related complexes F5 and F6 due to the similar fluorine substitution pattern. Their emission quantum yields are remarkably high for charged complexes in the CH2Cl2 solution. These results showed that Pd-catalyzed C-H bond arylation is a valuable synthetic approach for designing efficient emitters with tunable photophysical properties.

Novel cyclometallated 5-π-delocalized donor-1,3-di(2-pyridyl)benzene platinum(ii) complexes with good second-order nonlinear optical properties.

Five new platinum(ii) complexes bearing a cyclometallated 5-π-delocalized donor-1,3-di(2-pyridyl)benzene were prepared and fully characterized. Their second-order nonlinear optical (NLO) properties were determined by the Electric-Field Induced Second Harmonic generation (EFISH) technique, working in DMF solution with an incident wavelength of 1907 nm, whereas the dipole moments were determined by Density Functional Theory (DFT) calculations. Remarkably, the platinum(ii) complex with a cyclometallated 5-guaiazulene-CH[double bond, length as m-dash]CH-1,3-di(2-pyridyl)benzene appears as a very good candidate for application in photonics, being characterized by the largest second-order NLO response. Besides, it appeared that the nature of substituents on thiophene, chosen as π-delocalized moiety in position 5 of the 1,3-di(2-pyridyl)benzene, strongly affects the NLO properties.

Ruthenium(II)-carbonyl complexes containing two N-monodentate 1,8-naphthyridine ligands: active catalysis in transfer hydrogenation reactions.

The reaction of 2-aminonicotinaldehyde with 2- or 4-methoxyacetophenone in basic media leads to the new ligands 2-(4-methoxyphenyl)-1,8-naphthyridine and 2-(2-methoxyphenyl)-1,8-naphthyridine, respectively, in high yield. The reaction of these naphthyridine derivatives with [RuCl2(CO)2]n leads to the respective complexes cis-dicarbonyldichloridobis[2-(4-methoxyphenyl)-1,8-naphthyridine-κN8]ruthenium(II) and cis-dicarbonyldichloridobis[2-(2-methoxyphenyl)-1,8-naphthyridine-κN8]ruthenium(II), both [RuCl2(C15H12N2O)2(CO)2], in good yield. Both ruthenium(II) complexes display a slightly distorted octahedron with two cis carbonyl, two cis chloride and two cis naphthyridine ligands, the latter coordinated in a monodentate fashion through the N atom in the 8-position. Both complexes exhibit a moderate catalytic activity in the hydrogen-transfer reaction from propan-2-ol to acetophenone in the presence of a base, with 100% selectivity.

An investigation on the second-order nonlinear optical response of cationic bipyridine or phenanthroline iridium(iii) complexes bearing cyclometallated 2-phenylpyridines with a triphenylamine substituent.

The synthesis and characterisation of six new cationic iridium(iii) complexes bearing either 4,4'-di-tert-butyl-2,2'-bipyridine (dtBubpy) or 5-NO2-1,10-phenanthroline along with two cyclometallated 2-phenylpyridine derivative ligands, decorated with triphenylamine groups either meta or para to the Ir-CC^N bond or para to the Ir-NC^N bond, are reported. The second-order nonlinear optical (NLO) properties of all the compounds have been determined by the electric field induced second harmonic generation technique and show that the µßEFISH value can be tuned by the nature of the iridium coordination sphere. The dipole moment, µ, necessary to evaluate the quadratic hyperpolarizability ßEFISH, was theoretically determined. The linear optical properties of the complexes are also presented and rationalised by quantum-chemical calculations. One of the prepared iridium compounds was incorporated into a polystyrene film, affording the first example of a second-order NLO active polymeric film based on a cationic organometallic complex.

Photochromic DTE-Substituted-1,3-di(2-pyridyl)benzene Platinum(II) Complexes: Photomodulation of Luminescence and Second-Order Nonlinear Optical Properties.

We disclose a new family of photochromic cyclometalated platinum(II) complexes (PtDTE1 and PtDTE2), where a dithienylethene (DTE) unit is connected at the para-position of the central phenyl ring of (N^C^N) cyclometalated ligand, through two different linkages. Their syntheses are presented along with the X-ray characterizations of both the open and closed isomers of PtDTE1. The investigation of their photophysical properties is made, including absorption, photochromism, emission, and second-order nonlinear properties. We report a quantitative photoisomerization for both PtDTE1 and PtDTE2, irrespective of the nature of the connecting mode between the DTE unit and the platinum(II) moiety. The efficient photochromism allows a significant NLO photomodulation, both in solution and in thin films. In addition, we show that the photoluminescence of the PtDTE1 and PtDTE2 can be controlled by the open/closed isomerization of the DTE unit.

Phosphorescent cationic iridium(iii) complexes bearing a nonconjugated six-membered chelating ancillary ligand: a strategy for tuning the emission towards the blue.

This study concerns an assessment of the impact of the interruption of the electronic crosstalk between the pyridine rings in the ancillary ligand on the photoluminescence properties of the corresponding iridium(iii) complexes. Two new cationic Ir(iii) complexes, [Ir(dFmesppy)2(pmdp)]PF6, 1, and [Ir(mesppy)2(pmdp)]PF6, 2, [where dFmesppy is 2-(2,4-difluorophenyl)-4-mesitylpyridinato, mesppy is 4-mesityl-2-phenylpyridinato and pmdp is 2,2'-(phenylmethine)dipyridine, L1] possessing sterically congested cyclometalating ligands combined with the nonconjugated diimine ancillary N^N ligand are reported and their solution-state and thin film photophysical properties analyzed by both experimental and theoretical methods. The crystal structure of 1 confirms the formation of a six-membered chelate ring by the N^N ligand and illustrates the pseudo-axial configuration of the phenyl substituents. Upon photoexcitation in acetonitrile, both complexes exhibit a ligand-centered emission profile in the blue-green region of the visible spectrum. A significant blue-shift is observed in solution at room temperature compared to the analogous reference Ir(iii) complexes (R1 and R2) bearing 4,4'-di-tert-butyl-2,2'-bipyridine (dtBubpy) as the N^N ligand. The computational investigation demonstrates that the HOMO is mainly centered on the metal and on both cyclometalating aryl rings of the C^N ligands, whereas the LUMO is principally localized on the pyridyl rings of the C^N ligands. The photoluminescence quantum yield is reduced compared to the reference complexes, a probable consequence of the greater flexibility of the ancillary ligand.

Synthesis, Characterization, and Optoelectronic Properties of Iridium Complexes Bearing Nonconjugated Six-Membered Chelating Ligands.

We report the synthesis, characterization, and optoelectronic properties of a series of four new luminescent iridium(III) complexes, 1-4, of the form [Ir(C∧N)2(N∧N)]PF6 (where C∧N is the nonconjugated benzylpyridinato (bnpy) and N∧N is a neutral diimine ancillary ligand) with the goal of investigating the effect of the methylene spacer between the coordination moieties of the C∧N ligand on the optoelectronic properties of the complexes. The crystal structures of 1-3 illustrate two possible orientations of the methylene unit of the bnpy ligand. The formation of these two separate conformers is a result of the conformational flexibility of the bnpy ligand. In complexes 3 and 4, mixtures of the two conformers were observed by 1H NMR spectroscopy in CDCl3 at room temperature, whereas only a single conformer is detected for 1 and 2. Detailed DFT calculations corroborate NMR experiments, accounting for the presence and relative populations of the two conformers. The optoelectronic properties of all four complexes, rationalized by the theoretical study, demonstrate that the interruption of conjugation in the C∧N ligands results in a reduced electrochemical gap but similar triplet state energies and lower photoluminescence quantum yields in comparison to the reference complexes R1-R4. Depending on the nature of the N∧N ligand, we observe (1) marked variations of the ratio of the conformers at ambient temperature and (2) phosphorescence ranging from yellow to red.

Fluorescence Commutation and Surface Photopatterning with Porphyrin Tetradithienylethene Switches.

Four tetradithienylethene (DTE) substituted porphyrins, the free base 1H2 , and three metal derivatives (1Zn, 1Co, 1Ni), were synthesized and studied. These dyads, for which the DTE units are connected to the porphyrin's meso positions via a meta-phenyl spacer, exhibit reversible photochromic properties in all cases, with conversion to the photostationary state (PSS) up to 88 %, as confirmed by absorption and NMR spectroscopies. Compounds 1H2 and 1Zn are fluorescent in solution and display a red emission. Upon irradiation with UV light to trigger the closing of the DTEs, the fluorescence of both the free base and zinc porphyrin was very efficiently quenched in solution. The reversible, photo-switching of luminescence was retained in a tetra-DTE free-base porphyrin-doped polystyrene film, for which photo-patterning was demonstrated by confocal scanning microscopy. The tunable fluorescent properties of this multi-DTE framework render this compound of interest as a photo-rewritable fluorescent ink.

Controlling the emission in flexibly-linked (N

The synthesis, spectroscopic and theoretical characterizations of dinuclear Pt(ii) complexes where the two chromophoric units are connected though a polyether chain via either the central benzene ring of the tridentate ligand dpyb (Pt-2), or the phenylacetylide ligand (Pt-3), are described. The spacer, which contains four oxyethylene -CH2CH2O- units, is flexible and long enough to allow a self-association of the Pt units by folding, as shown by DFT calculations. Comparison of the photophysical properties of the dinuclear complex Pt-2 with those of the mononuclear complex Pt-1, used as reference, demonstrates the key role played by the linker group in the interaction processes. In addition, the emission of complex Pt-2 was found to be affected by the temperature, nature of the solvent, and cation coordination as evidenced by luminescence and 1H NMR studies. The interacting processes are highly dependent on the solvent polarity that controls the - extended vs folded - arrangement and, consequently, induces solvatochromic shifts. This unique photophysical behavior of Pt-2 allows the modulation of the emission from green to deep-red (up to 125 nm) over the visible part of the spectrum. By contrast, complex Pt-3 has a high propensity to form a red-shifted intense emissive excimer. DFT and TD-DFT investigations of the excimers in Pt-2 and Pt-3 consistently show a much stronger interaction in the latter complex.

Bay-Region Functionalisation of Ar-BIAN Ligands and Their Use Within Highly Absorptive Cationic Iridium(III) Dyes.

We report the synthesis, UV-vis absorption, electrochemical characterisation, and DFT studies of five panchromatic, heteroleptic iridium complexes (four of which are new) supported by Ar-BIAN ligands. In particular, the synthesis of an ester-functionalised Ar-BIAN ligand was carried out by a mechanochemical milling approach, which was advantageous over conventional metal templating solution methods in terms of reaction time and product purity. The introduction of ester and carboxylate functionalities at the bay region of the acenaphthene motif increases each ligand's π-accepting capacity and imparts grafting capabilities to the iridium complexes. These complexes have absorption profiles that surpass the renowned N3 dye [Ru(dcbpy)2(NCS)2] (dcbpy = 4,4'-dicarboxy-2,2'-bipyridine), making them of interest for solar-energy-harvesting applications.

An Unprecedented Family of Luminescent Iridium(III) Complexes Bearing a Six-Membered Chelated Tridentate C

A new family consisting of three luminescent neutral Ir(III) complexes with the unprecedented [Ir(C^N^C)(N^N)Cl] architecture, where C^N^C is a bis(six-membered) chelating tridentate tripod ligand derived from 2-benzhydrylpyridine (bnpy) and N^N is 4,4'-di-tert-butyl-2,2'-bipyridine (dtBubpy), is reported. X-ray crystallography reveals an unexpected and unusual double C-H bond activation of the two distal nonconjugated phenyl rings of the bnpy coupled with a very short Ir-Cl bond trans to the pyridine of the bnpy ligand. Depending on the substitution on the bnpy ligand, phosphorescence, ranging from yellow to red, is observed in dichloromethane solution. A combined study using density functional theory (DFT) and time-dependent DFT (TD-DFT) corroborates the mixed charge-transfer nature of the related excited states.

Metal Complexes for Two-Photon Photodynamic Therapy: A Cyclometallated Iridium Complex Induces Two-Photon Photosensitization of Cancer Cells under Near-IR Light.

Photodynamic therapy (PDT) uses photosensitizers (PS) which only become cytotoxic upon light-irradiation. Transition-metal complexes are highly promising PS due to long excited-state lifetimes, and high photo-stabilities. However, these complexes usually absorb higher-energy UV/Vis light, whereas the optimal tissue transparency is in the lower-energy NIR region. Two-photon excitation (TPE) can overcome this dichotomy, with simultaneous absorption of two lower-energy NIR-photons populating the same PS-active excited state as one higher-energy photon. We introduce two low-molecular weight, long-lived and photo-stable iridium complexes of the [Ir(N^C)2 (N^N)]+ family with high TP-absorption, which localise to mitochondria and lysosomal structures in live cells. The compounds are efficient PS under 1-photon irradiation (405 nm) resulting in apoptotic cell death in diverse cancer cell lines at low light doses (3.6 J cm-2 ), low concentrations, and photo-indexes greater than 555. Remarkably 1 also displays high PS activity killing cancer cells under NIR two-photon excitation (760 nm), which along with its photo-stability indicates potential future clinical application.

Contrasted photochromic and luminescent properties in dinuclear Pt(ii) complexes linked through a central dithienylethene unit.

We disclose two unprecedented complexes built with a central dithienylethene photochrome connecting two cyclometalated Pt(ii) moieties either on the reactive carbon atoms or on the lateral non-reactive carbon atoms of the photochrome. The two systems show vastly different properties that are rationalised thanks to quantum-chemical calculations.

Sequential double second-order nonlinear optical switch by an acido-triggered photochromic cyclometallated platinum(II) complex.

An unprecedented DTE-based Pt(II) complex, 2(o), which stands as the first example of a sequential double nonlinear optical switch, induced first by protonation and next upon irradiation with UV light is presented.

Aggregation effect on the luminescence properties of phenylbipyridine Pt(II) acetylide complexes. A theoretical prediction with experimental evidence.

We report a combined theoretical and experimental study of both the structural and optical properties of phosphorescent cyclometalated square-planar (phenylbipyridyl)platinum(II) acetylide complexes, namely (Pt(tBu2-CN̂N)(C≡C-Ph)] and (Pt(hex2-CN̂N)(C≡C-thienyl)] that exhibit, at high concentrations, an additional emission band at longer wavelength. The geometry optimizations of both the ground and the lowest triplet excited states of the considered monomers and different possible dimers have been performed in solution using several density functional theory (DFT) functionals corrected for dispersion effects. For the dimers, which are shown to exhibit a head-to-tail configuration, a significant shortening of the Pt···Pt distance, compared to that in the ground state, is observed in the first triplet state. Moreover, we show that trimeric species are highly improbable in solution. The UV-visible absorption spectra of the complexes are well rationalized using a vertical time-dependent DFT (TD-DFT) protocol relying on a global hybrid exchange-correlation functional. Finally, the new emission band at high concentration of the complexes can be assigned to a metal-metal to ligand charge transfer excited state ((3)MMLCT).

Benzothiophene or benzofuran bridges in diaryl ethenes: two-step access by pd-catalyzed C-H activation and theoretical/experimental studies on their photoreactivity.

A series of terarylenes incorporating benzothiophene (BT)/benzofuran (BF) as the central ethene unit was synthesised by using sequential Pd-catalysed C-H activation reactions. This new methodology allows the easy modification of the nature of the pendant heteroarene groups. Diaryl ethene (DAE) derivatives with thiophene, thiazole, pyrrole, isoxazole and pyrazole rings were prepared. A large number of asymmetrical DAEs are easily accessible by this new method in both the BT and BF series. The study of their photochromic properties in solution revealed that the nature of the heteroarene and of the central unit drastically modify their photochromic behaviour. TD-DFT calculations were performed to assess the nature of the relevant excited states.