Search

ispartof: CHEMPHOTOCHEM status: Published online

The photophysical properties, especially the intersystem crossing (ISC) of two heavy-atom-free BODIPY derivatives with twisted π-conjugated frameworks (benzo[b]-fused BODIPY, BDP-B; and [a]phenanthrene-fused BODIPY, BDP-P), are studied with steady-state and time-resolved optical and electron paramagnetic resonance (TREPR) spectroscopic methods as well as with ADC(2) theoretical investigations. Interestingly, BDP-B has a planar π-conjugation framework, but it displays weaker UV-vis absorption (ε = 3.8 × 104 M-1 cm-1 at 569 nm) and fluorescence (ΦF < 0.1%), a short-lived singlet-excited state (fluorescence lifetime, τF = 0.2 ns), and a long-lived triplet state (τT = 132.3 μs). In comparison, the more twisted BDP-P shows stronger UV-vis absorption (ε = 9.8 × 104 M-1 cm-1 at 640 nm) and fluorescence (ΦF = 70%), longer singlet-excited-state lifetime (τF = 6.4 ns), and shorter triplet-state lifetime (τT = 18.9 μs). In contrast to helicenes (ΦT = ca. 90%), the ISC of BDP-P and BDP-B is nonefficient (ΦT < 23%). The electron spin selectivity of the ISC of the derivatives is different, manifested by the phase pattern of the TREPR spectra as AAEAEE and EEEAAA for BDP-B and BDP-P, respectively. The spatially confined T1 state wave function of the twisted molecule keeps the T1 state energy high (1.44-1.61 eV). A dark S1 state was identified for BDP-B. This work demonstrated that the twisted π-conjugated framework does not necessarily induce efficient ISC and we found a dark singlet state for BODIPY, which is rare. ispartof: JOURNAL OF PHYSICAL CHEMISTRY B vol:125 issue:23 pages:6280-6295 ispartof: location:United States status: published

Two indoles linked by a C–C bond have recently emerged as promising scaffolds in medicinal chemistry. Their synthesis, however, involves a multitude of reaction steps. So far, the direct C–H/C–H cr...

The interplay between noncovalent interactions involving metal complexes may lead to the formation of aggregates (i.e., ground state dimers, trimers, n-mers, etc.), and this is often linked to dramatic changes in their physical and chemical properties as compared to the original properties of the isolated units. Dimers and trimers can also be formed in the excited state potential energy surfaces, i.e., excimers. Excimers are short-lived but are also often characterized by different optical properties from those of the isolated units. Understanding the nature of noncovalent interactions and the presence or not of cooperativity effects in both aggregates and excimers is thus extremely important to rationalize these variations. In this study, we present computational investigations on isoquinolinyl pyrazolate Pt(II) complexes. Our results highlight that cooperativity effects between noncovalent interactions, which are modulated by sterically demanding substituents and metallophilic Pt···Pt interactions, are present only on certain investigated excimers. We use density functional theory (DFT) calculations to examine the cooperativity effects and the changes in the photophysical properties. Different descriptors of cooperativity effects between noncovalent interactions, including the synergetic, genuine nonadditive, and total interaction energies, were evaluated for a series of Pt(II) aggregates and excimers. In addition, energy decomposition analysis (EDA) calculations were performed to rationalize the origins of the cooperative effects. The cooperative effects in trimer excimers (in their lowest triplet excited state, i.e., T1) led to shortened Pt···Pt contacts as compared to the trimer aggregates. Furthermore, this synergy between noncovalent interactions is ultimately responsible for the formation of the excimers and the striking changes in the measured photophysical properties. More in detail, we report a change in the character of the lowest-lying triplet excited state when going from dimer excimers (i.e., of mixed triplet ligand-centered and triplet metal-to-ligand charge transfer (3LC/3MLCT) character) to trimer excimers (i.e., of triplet metal-metal-to-ligand charge transfer (3MMLCT) character). The EDA reveals that the total interaction energy on trimer excimers is subtly controlled by the electrostatic and dispersion terms. ispartof: INORGANIC CHEMISTRY vol:59 issue:24 pages:18253-18263 ispartof: location:United States status: published

Here, we report the synthesis of two isomeric BODIPY-based fluorescent molecules with a diethylamino donor group and an acetyl acceptor group at positions 5 and 2 (or 3), respectively, on the boron dipyrromethene core. The structure of the new BODIPY dyes is similar to Prodan, probably the most widely used solvatochromic probe, but with the donor and acceptor groups attached to an electron-poor heteroaromatic core. Interestingly, these BODIPY dyes exhibit unusual spectroscopic and photophysical properties, involving inverse solvatochromic behavior. An in-depth study of the solvent effects and quantum-chemical calculations have been performed to assess the basis for such spectroscopic properties and the effect of the position of the substitution. This work points towards a rational design of new fluorescent probes, based on understanding their spectroscopic and photophysical behavior.

Complexes [{Pt(C^C*)(μ-pz)}2] (HC^C*A = 1-(4-(ethoxycarbonyl)phenyl)-3-methyl-1H-imidazol-2-ylidene 1a, HC^C*B = 1-phenyl-3-methyl-1H-imidazol-2-ylidene 1b) react with methyl iodide (MeI) at room temperature in the dark to give compounds [{PtIV(C^C*)Me(μ-pz)}2(μ-I)]I (C^C*A2a, C^C*B2b). The reaction of 1a with benzyl bromide (BnBr) in the same conditions afforded [Br(C^C*A)PtIII(μ-pz)2PtIII(C^C*A)Bn] (5a), which by heating in BnBr(l) became [{PtIV(C^C*A)Bn(μ-pz)}2(μ-Br)]Br (6a). Experimental investigations and density functional theory (DFT) calculations on the mechanisms of these reactions from 1a revealed that they follow a SN2 pathway in the two steps of the double oxidative addition (OA). Based on the DFT investigations, species such as [(C^C*A)PtIII(μ-pz)2PtIII(C^C*A)R]X (RX = MeI Int-Me, BnBr Int-Bn) and [(C^C*A)PtII(μ-pz)2PtIV(C^C*A)(R)X] (RX = MeI Int′-Me, BnBr Int′-Bn) were proposed as intermediates for the first and the second OA reactions, respectively. In order to put the mechanisms on firmer grounds, Int-Me was prepared as [(C^C*A)PtIII(μ-pz)2PtIII(C^C*A)Me]BF4 (3a′) and used to get [I(C^C*A)PtIII(μ-pz)2PtIII(C^C*A)Me](4a), [(C^C*A)PtII(μ-pz)2PtIV(C^C*A)(Me)I](Int′-Me), and [{PtIV(C^C*)Me(μ-pz)}2(μ-I)]BF4 (2a′). The single-crystal X-ray structures of 2a, 2b, 3a′, and 5a along with the mono- and bi-dimensional 1H and 195Pt{1H} NMR spectra of all the named species allowed us to compare structural and spectroscopic data for high-valent complexes with the same core [{Pt(C^C*)(μ-pz)}2] but different oxidation states., This work was supported by the Spanish Ministerio de Economia y Competitividad (Ministerio de Ciencia Innovacion y Universidades)/FEDER (Project PGC2018-094749-B-I00), by the Gobierno de Aragon (Grupo E17_20R: Química Inorgánica y de los Compuestos Organometálicos) and by Internal Funds KU Leuven and FWO. L.A. acknowledges the support of a grant from the Gobierno de Aragón.

Novel heteropolymetallic architectures have been built by integrating Pd, Au and Ag systems. The dinuclear [(CNC)(PPh3)Pd-G11M(PPh3)](ClO4) (G11M=Au (3), Ag (4); CNC=2,6-diphenylpyridinate) and trinuclear [{(CNC)(PPh3)Pd}2G11M](ClO4) (G11M=Au (6), Ag (5)) complexes have been accessed or isolated. Structural and DFT characterization unveil striking interactions of one of the aryl groups of the CNC ligand(s) with the G11M center, suggesting these complexes constitute models of transmetallation processes. Further analyses allow to qualitatively order the degree of transfer, proving that Au promotes the highest one and also that Pd systems favor higher degrees than Pt. Consistently, Energy Decomposition Analysis calculations show that the interaction energies follow the order Pd−Au > Pt−Au > Pd−Ag > Pt−Ag. All these results offer potentially useful ideas for the design of bimetallic catalytic systems., This work was supported by the Spanish MICIU/FEDER (Project PGC2018-094749-B−I00) and the Gobierno de Aragón (Grupo E17_20R). BIFI (Instituto de Biocomputación y Física de Sistemas Complejos) and CESGA (Centro de Supercomputación de Galicia) are acknowledged for allocation of computational resources.. D.C. also thanks the Gobierno de Aragón for a grant. D.E. acknowledges KU Leuven Internal Funds and FWO.

The effects of the electron-donating capacity altered by heteroatom substituents on the electronic structures, photophysical properties, and excited-state intramolecular proton transfer (ESIPT) processes of 3HX analogues (3HF, 3HQ, 3HTF, and 3HSO where X = O, NH, S, and SO2, respectively) have been investigated by both static calculations and dynamic simulations using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods at B3LYP/TZVP level for ground state (S0) and excited-state (S1), respectively. The static results indicate that the intramolecular hydrogen bonds of all molecules are strengthened in the S1 state, confirmed by the red-shift of IR vibrational spectra and the topology analysis. Heteroatom substitutions cause the red-shift on enol absorption and keto emission spectra of 3HX with relatively larger Stoke shift corresponding to their HOMO−LUMO gaps compared with that of 3HF. Frontier molecular orbitals (MOs) show that upon the photoexcitation, the charge redistribution between the proton donor and proton acceptor groups have induced the ESIPT process. Moreover, the potential energy curves (PECs) of proton transfer (PT) processes of all molecules reveal that the PT processes of all molecules are most likely to proceed in the S1 state because of low barrier and exothermic reaction. The chance of ESIPT for all molecules is in this order: 3HSO > 3HTF > 3HF > 3HQ. The results of dynamic simulations confirm that the ESIPT processes of all molecules easily occur with the ultrafast time scale (48, 55, 60, 70 fs for 3HSO, 3HTF, 3HF, and 3HQ, respectively). Furthermore, the PT time is anti-correlated with the electronegativity of heteroatoms in 3HX, supported by Mulliken analysis. The ESIPT process of 3HSO is the fastest among 3HX in accordance with its highest intramolecular hydrogen bond strength, lowest PT barrier, and highest exothermic reaction. Nevertheless, after the ESIPT is complete, the twisted structure of 3HSO has initiated the conical intersection, leading to no keto emission observed in the experiment.

The reliable calculation of phosphorescence energies of phosphor materials is at the core of designing efficient phosphorescent organic light-emitting diodes (PhOLEDs). Therefore, it is of paramount importance to have a robust computational protocol to perform those calculations in a black-box manner. In this work, we use Domain-Based Local Pair Natural Orbital Coupled Cluster theory with single, double, and perturbative triple excitation (DLPNO-CCSD(T)) calculations to attain the phosphorescence energies of a large pool of Pt(II) complexes. Several approaches to incorporate relativistic effects in our calculations were tested. In addition, we have used the DLPNO-CCSD(T) values (i.e., our best theoretical values) to assess the performance of different flavors of density functional theory including pure, hybrid, meta-hybrid, and range-separated functionals. Among the tested functionals, the M06HF functional provides the best values compared with the DLPNO-CCSD(T) ones, with a mean absolute deviation (MAD) value of 0.14 eV. In its turn, and thanks to the increased accuracy achieved in the calculation of phosphorescence energies, we also demonstrate that not all of the investigated complexes emit from their lowest-lying triplet state (T1). The outlier complexes include different complex photophysical scenarios and both Kasha and anti-Kasha types of complexes. Finally, we provide a general computational protocol to pre-screen whether T1 is actually the emissive state and to accurately calculate the phosphorescence energies of Pt(II) complexes. ispartof: INORGANIC CHEMISTRY vol:60 issue:22 pages:17230-17240 ispartof: location:United States status: published

DFT investigations on the ground (GS) and the first triplet (T1) excited state potential energy surfaces (PES) were performed on a new series of platinum-butterfly complexes, [{Pt(C∧C*)(μ-Rpz)}2] (Rpz: pz, 1; 4-Mepz, 2; 3,5-dmpz, 3; 3,5-dppz, 4), containing a cyclometalated NHC in their wings. The geometries of two close-lying local minima corresponding to butterfly spread conformers, 1s–4s, and butterfly folded ones, 1f–4f, with long and short Pt–Pt separations, respectively, were optimized in the GS and T1 PES. A comparison of the GS and T1 energy profiles revealed that an opposite trend is obtained in the relative stability of folded and spread conformers, the latter being more stabilized in their GS. Small ΔG (s/f) along with small-energy barriers in the GS support the coexistence of both kinds of conformers, which influence the photo- and mechanoluminescence of these complexes. In 5 wt % doped PMMA films in the air, these complexes exhibit intense sky-blue emissions (PLQY: 72.0–85.9%) upon excitation at λ ≤ 380 nm arising from 3IL/MLCT excited states, corresponding to the predominant 1s–4s conformers. Upon excitation at longer wavelengths (up to 450 nm), the minor 1f–4f conformers afford a blue emission as well, with PLQY still significant (40%–60%). In the solid state, the as-prepared powder of 4 exhibits a greenish-blue emission with QY ∼ 29%, mainly due to 3IL/3MLCT excited states of butterfly spread molecules, 4s. Mechanical grinding resulted in an enhanced and yellowish-green emission (QY ∼ 51%) due to the 3MMLCT excited states of butterfly folded molecules, 4f, in such a way that the mechanoluminescence has been associated with an intramolecular structural change induced by mechanical grinding., This work was supported by the Spanish Ministerio de Economia y Competitividad (Ministerio de Ciencia Innovacion y Universidades)/FEDER (Project PGC2018–094749–B-I00), by the Gobierno de Aragon (Grupo E17_20R: Quimica Inorganica y de los Compuestos Organometallicos), and by Internal Funds KU Leuven.

A 48-membered macrocyclic ZnII-Schiff base complex DAS (Dual Anion Sensor) containing protonated imine has been synthesized and characterised. The single crystal X-ray structural analysis reveals a tetranuclear complex cation [Zn4(LH3)(NO3)5]2+ counterbalanced by a [Zn(NO3)4]2− anion. DAS acts as a dual anion sensor which can selectively detect fluoride and acetate in aqueous methanolic solution by change in UV-vis spectra as well as by fluorescence enhancement. A probable mechanistic pathway has been proposed and DFT calculations corroborate well with the experimental data. The calculated limit of detection for F− and AcO− ions was 0.18 and 1.98 μM, and 0.15 and 1.8 μM from UV and FL data, respectively. Interestingly, DAS behaves as an INHIBIT logic gate with F−/AcO− and H+ as inputs. To the best of our knowledge, this is the first example where a macrocyclic Zn-complex serves as an INHIBIT logic gate. Practical utility of DAS has been explored by successful detection of F− in commercially available toothpaste as well as solid state detection of F− and AcO−.

The photophysical properties of a heavy atom-free BODIPY derivative with a twisted π-conjugated framework were studied. Efficient intersystem crossing (ISC quantum yield: 56%) and an exceptionally long-lived triplet state were observed (4.5 ms in solid polymer film matrix and 197.5 μs in solution). Time-resolved electron paramagnetic resonance (TREPR) spectroscopy and DFT computations confirmed the delocalization of the triplet state on the whole twisted π-conjugated framework and the zero-field-splitting (ZFS) D parameter of D = -69.5 mT, which is smaller than that of 2,6-diiodoBODIPY (D = -104.6 mT). The electron spin polarization (ESP) phase pattern of the triplet state TREPR spectrum of the twisted BODIPY is (a, a, e, a, e, e), which is different from that of 2,6-diiodo BODIPY (e, e, e, a, a, a), indicating that the electron spin selectivity of the ISC of the twisted structure is different from that of the spin orbital coupling effect. According to the computed spin-orbit coupling matrix elements (0.154-1.964 cm-1), together with the matched energy of the S1/Tn states, ISC was proposed to occur via S1→T2/T3. The computational results were consistent with TREPR results on the electron spin selectivity (the overpopulation of the TY sublevel of the T1 state). The advantage of the long-lived triplet state of the twisted BODIPY was demonstrated by its efficient singlet oxygen (1O2) photosensitizing (ΦΔ = 50.0%) even under a severe hypoxia atmosphere (pO2 = 0.2%, v/v). A high light toxicity (EC50 = 1.0 μM) and low dark toxicity (EC50 = 78.5 μM) were observed for the twisted BODIPY, and thus the cellular studies demonstrate its potential as a novel potent heavy atom-free photodynamic therapy (PDT) agent. ispartof: PHYSICAL CHEMISTRY CHEMICAL PHYSICS vol:23 issue:14 pages:8641-8652 ispartof: location:England status: published

Different perylene-3,4:9,10-bis(dicarboximide) (abbreviated as perylenebisimides, or simply PBI) compounds (MT-PBI, DT-PBI, MP-PBI and DP-PBI) with thienyl and phenyl substituents at the bay position were prepared to study the effect of substitution on the photophysical properties, especially the intersystem crossing (ISC) efficacy. We found that the derivative with a monothienyl substituent (MT-PBI) shows efficient ISC (singlet oxygen quantum yield ΦΔ = 72%) and longer triplet state lifetime (τT = 64.4 μs) as compared to reference compounds (derivative with monophenyl substituent at bay position, MP-PBI, ΦΔ = 23% and τT = 48.5 μs). Theoretical computations reveal that the ISC efficiency is dependent on the magnitude of the spin orbit couplings (SOC) between the singlet and triplet excited states, and the SOC matrix element is up to 2 cm−1 for compound showing the highest ISC efficiency. Femtosecond transient absorption spectra show the ISC rate constant of 8 × 109 s−1 for MT-PBI, and no charge transfer exists. Photo-driven electron transfer was observed with the PBI derivatives in the presence of sacrificial electron donor triethanolamine (TEOA), and reversible formation of PBI radical anion (PBI−•) was observed, which shows absorption in the range of 600 nm–800 nm and 900 nm–1000 nm. Delayed fluorescence (P-type) in MT-PBI was also observed (τT = 31.0 μs). These finding are useful for the design of PBI-derived heavy atom-free compounds to be used as triplet photosensitizers.

In this contribution, we present a computational protocol to predict anti-Kasha photoluminescence. The herein developed protocol is based on state-of-the-art quantum chemical calculations and excited-state decay rate theories (i.e., thermal vibration correlation function formalism), along with appropriate kinetic models which include all relevant electronic states. This protocol is validated for a series of azulene derivatives. For this series, we have computed absorption and emission spectra for both their first and second excited states, their radiative and nonradiative rates, as well as fluorescence yields from the two different excited states. All the studied azulene derivatives are predicted to exclusively display anomalous anti-Kasha S2 emission. A quantitative agreement for the herein computed excited-state spectra, lifetimes, and fluorescence quantum yields is obtained with respect to the experimental values. Given the increasing interest in anti-Kasha emitters, we foresee that the herein developed computational protocol can be used to prescreen dyes with the desired aforementioned anomalous photoluminescence properties. ispartof: JOURNAL OF PHYSICAL CHEMISTRY A vol:124 issue:36 pages:7228-7237 ispartof: location:United States status: published

In this contribution we present a computational protocol to predict anti-Kasha photoluminescence. The herein developed protocol is based on state-of-the-art quantum chemical calculations and excited state decay rate theories (i.e., thermal vibration correlation function formalism), along with appropriate kinetic models which include all relevant electronic states. This protocol is validated for a series of azulene derivatives. For this series, we have computed absorption and emission spectra for both their first and second excited states, their radiative and non-radiative rates as well as fluorescence yields from the two different excited states. All the studied azulene derivatives are predicted to exclusively display anomalous anti-Kasha S2 emission. A quantitative agreement for the herein computed excited state spectra, lifetimes and fluorescence quantum yieldsis obtained with respect to the experimental values. Given the increasing interest on anti-Kasha emitters, we foresee that the herein developed computational protocol can be used to pre-screen dyes with the desired aforementioned anomalous photoluminescence properties.

A class of D-π-A compounds that can be used as dyes for applications in polymer solar cells has theoretically been designed and studied, on the basis of the dyes recently shown by experiment to have the highest power conversion efficiency (PCE), namely the poly[4,8-bis(5-(2-butylhexylthio)thiophen-2-yl)benzo[1,2-b:4,5-b’]dithiophene-2,6-diyl-alt-TZNT] (PBDTS-TZNT) and poly[4,8-bis(4-fluoro-5-(2-butylhexylthio)thiophen-2-yl)benzo[1,2-b:4,5-b’]dithiophene-2,6-diyl-alt-TZNT] (PBDTSF-TZNT) substances. Electronic structure theory computations were carried out with density functional theory and time-dependent density functional theory methods in conjunction with the 6−311G (d, p) basis set. The PBDTS donor and the TZNT (naphtho[1,2-c:5,6-c]bis(2-octyl-[1,2,3]triazole)) acceptor components were established from the original substances upon replacement of long alkyl groups within the thiophene and azole rings with methyl groups. In particular, the effects of several π-spacers were investigated. The calculated results confirmed that dithieno[3,2-b:2′,3′-d] silole (DTS) acts as an excellent π-linker, even better than the thiophene bridge in the original substances in terms of well-known criteria. Indeed, a PBDTS-DTS-TZNT combination forms a D-π-A substance that has a flatter structure, more rigidity in going from the neutral to the cationic form, and a better conjugation than the original compounds. The highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy gap of such a D-π-A substance becomes smaller and its absorption spectrum is more intense and red-shifted, which enhances the intramolecular charge transfer and makes it a promising candidate to attain higher PCEs.

International audience; Controlling the electronic coupling between electron donor and acceptor subunits in a dyad is pivotal for the development of novel organic materials, for instance, thermally activated delayed fluorescence (TADF) materials and triplet photosensitizers. Herein, we prepared two compact electron donor/acceptor dyads based on phenothiazine (PTZ) and naphthalimide (NI) with different conformation restrictions induced by the C–N (NI-N-PTZ) or C–C (NI-C-PTZ) linkers. The effect of electronic coupling (matrix elements, VDA) on the photophysical properties, especially the intersystem crossing (ISC) and the TADF, were investigated. NI-C-PTZ shows stronger ground-state electronic coupling (VDA = 2548 cm–1) compared to NI-N-PTZ (VDA = 870 cm–1). TADF was observed only for NI-N-PTZ due to its smaller electronic coupling. Time-resolved electron paramagnetic resonance (TREPR) spectroscopy indicated the presence two triplet excited states and three ISC mechanisms in NI-N-PTZ with different electron spin polarizations (ESP): radical pair ISC (RP-ISC) and spin–orbital charge transfer ISC (SOCT-ISC) for one triplet state, and spin–orbital coupling ISC (SO-ISC) for another. Moreover, for the second one, an inversion of the electron spin polarization (ESP) was observed at 0.5–1.1 μs delay time. NI-N-PTZ represents a rare example for compact electron donor/acceptor dyad showing TADF emission in the red spectral region.

The vast majority of polyhedral assemblies prepared by combining organic bent ligands and ``photophysically innocent'' palladium(II) metal ions are nonemissive. We report here a simple strategy to switch on the luminescence properties of a polyhedral assembly by combining a thermally activated delayed fluorescence (TADF) organic emitter based on a dipyridylcarbazole ligand scaffold with Pd2+ ions, giving rise to a luminescent Pd6L12 molecular cube. The assembly is capable of encapsulating within its cavity up to three molecules per cage of fluorescein, in its neutral lactone form, and up to two molecules of Rose Bengal in its dianionic quinoidal form. Photoinduced electron transfer (PeT) between the photoactive cage and the encapsulated Fluorescein and photoinduced energy transfer (PET) from the cage to encapsulated Rose Bengal have been observed by steady-state and time-resolved emission spectroscopy.

A tridentate N,N,O donor ligand 2,4-dichloro-2-[(2-piperazine-4-yl-ethylimino)-methyl]-phenol (HL) was designed, and eight new ZnII and CdII complexes, namely, [Zn(LH)(SCN)2] (1), [Zn(LH)(N3)2] (2), [Zn(LH)(NO2)2] (3), [Zn(LH)(dca)(OAc)] (4), [Cd2(LH)2(SCN)4] (5), [Cd(LH)(N3)2] (6), [Cd(LH)(NO2)2] (7), and [Cd(LH)(dca)(OAc)] (8) [where dca = dicyanamide anion] were synthesized. Five of them (1, 2, 4, 5, 7) were structurally characterized through single-crystal X-ray diffraction analysis. H-Bonding interactions are found to be the major stabilizing factor for crystallization in the solid state. Experimental and computational studies were performed in cooperation to provide a rationalization of the photoluminescence properties of those complexes. The quantum yields are anion-dependent, with enhanced efficiencies in the following order: LH < Cd-SCN(5) < Cd-dca(8) < Cd–N3(6) < Cd-NO2(7) < Zn-dca(4) < Zn–N3(2) < ZnNO2(3) < ZnSCN(1). By using quantum chemical calculations we rationalized the above trends. Moreo...

There is growing interest in the bis-tridentate Ir(III) emitters as they are expected to display both improved emission efficiency and improved photostability. Herein, we turned to the new emitters m2h-1–3 and m6h-1–3, bearing a pincer carbene ancillary and a chromophoric chelate derived from judiciously selected phenyl-pyrimidine-pyrazole entities (pzm2hF)H2 and (pzm6hF)H2, which differ in terms of the location of phenyl and pyrazole substituents on the central pyrimidine. Density functional theory calculations revealed a notable change in the spin density distribution from the pyrimidine-pyrazolate entity in m2h to the pyrimidine-phenyl fragment in m6h. As a consequence, the m6h emitters exhibited both shortened emission lifetimes and improved stabilities during extensive photolysis in solution, while corresponding organic light-emitting diodes (OLEDs) doped with green-emitting m6h-1 and sky-blue-emitting m6h-2 and m6h-3 exhibited external quantum efficiencies of 17.6, 15.9, and 17.6%, respectively, sup...

Photoinduced electron transfer (PET) plays relevant roles in many areas of chemistry, including charge separation processes in photovoltaics, natural and artificial photosynthesis, and photoluminescence sensors and switches. As in many other photochemical scenarios, the structural and energetic factors play relevant roles in determining the rates and efficiencies of PET and its competitive photodeactivation processes. Particularly, in the field of fluorescent sensors and switches, intramolecular PET is believed (in many cases without compelling experimental proof) to be responsible of the quench of fluorescence. There is an increasing experimental interest in fluorophore's molecular design and on achieving optimal excitation/emission spectra, excitation coefficients, and fluorescence quantum yields (importantly for bioimaging purposes), but less efforts are devoted to fundamental mechanistic studies. In this Account, I revise the origins of the fluorescence quenching in some of these systems with state-of-the-art quantum chemical tools. These studies go beyond the common strategy of analyzing frontier orbital energy diagrams and performing PET thermodynamics calculations. Instead, the potential energy surfaces (PESs) of the lowest-lying excited states are explored with time-dependent density functional theory (TD-DFT) and complete active space self-consistent field (CASSCF) calculations and the radiative and nonradiative decay rates from the involved excited states are computed from first-principles using a thermal vibration correlation function formalism. With such a strategy, this work reveals the real origins of the fluorescence quenching, herein entitled as dark-state quenching. Dark states (those that do not absorb or emit light) are often elusive to experiments and thus, computational investigations can provide novel insights into the actual photodeactivation mechanisms. The success of the dark-state quenching mechanism is demonstrated for a wide variety of fluorescent probes, including proton, cation and anion targets. Furthermore, this mechanism provides a general picture of the fluorescence quenching which englobes intramolecular charge-transfer (ICT), ratiometric quenching, and those radiationless mechanisms believed to be originated by PET. Finally, this Account provides for the first time a computational protocol to quantitatively estimate this phenomenon and provides the ingredients for the optimal design of fluorescent probes from first principles.

EZ-C acknowledges the University of St Andrews for financial support. IDWS acknowledges support from EPSRC (EP/J009016) and the European Research Council (grant 321305). IDWS also acknowledges support from a Royal Society Wolfson research merit award. DJ acknowledges the European Research Council (grant: 278845) and the RFI Lumomat for financial support. We present the first examples of dynamic supramolecular systems composed of cyclometalated Ir(III) complexes of the form of [Ir(C^N)2(N^N)]PF6 (where C^N is mesppy = 2-phenyl-4-mesitylpyridinato and dFmesppy = 2-(4,6-difluorophenyl)-4-mesitylpyridinato and N^N is 4,4':2',2'':4'',4'''-quaterpyridine, qpy) and zinc tetraphenylporphyrin (ZnTPP), assembled through non-covalent interactions between the distal pyridine moieties of the qpy ligand located on the iridium complex and the zinc of the ZnTPP. The assemblies have been comprehensively characterized by a series of analytical techniques (1H NMR titration experiments, 2D COSY and HETCOR NMR spectra and low temperature 1H NMR spectroscopy) and the crystal structures have been elucidated by X-ray diffraction. The optoelectronic properties of the assemblies and the electronic interaction between the iridium and porphyrin chromophoric units have been explored with detailed photophysical measurements, supported by time-dependent density functional theory (TD-DFT) calculations. Postprint

ispartof: ADVANCED FUNCTIONAL MATERIALS vol:30 issue:25 status: published

The use of tris(bidentate) Ir(III) complexes as light active components in phosphorescent organic light-emitting diodes (PhOLEDs) is currently the state-of-the-art technology to attain long-lasting and highly performing devices. Still, further improvements of their operational lifetimes are required for their practical use in lighting and displays. Facial/meridional stereoisomerism of the tris(bidentate) Ir(III) architectures strongly influences their emissive properties and thereto their PhOLEDs performances and operational device stabilities. This work underpins at the first-principles level the different excited state reactivities of facial and meridional stereoisomers of a series of tris(bidentate) Ir(III) complexes, which is found to originate in the presence of distinct triplet metal-centered (3MC) deactivation pathways. These deactivation pathways are herein presented for the first time for the meridional isomers. Finally, we propose some phosphor design strategies. ispartof: INORGANIC CHEMISTRY vol:57 issue:19 pages:12106-12112 ispartof: location:United States status: published

The phenoxido-bridged [Cu-2] complex [Cu-2(-H(4)L1)(-OH)((1,3)-NO3)(NO3)(OH2)]H2O (1) and its hierarchical [Cu-4] and [Cu-5] assemblies [Cu-4(-H(4)L1)(2)(-OH)(2)((1,3)-ClO4)(OH2)(2)](ClO4)(3)2H(2)O (2) and [Cu-5(-H(4)L1)(2)((3)-OH)(2)((1,3)-O2CCF3)(2)(O2CCF3)(2)](CF3COO)(2) (3) were obtained from the reactions of H(5)L1 (2,6-bis-\(1,3-dihydroxy-2-methylpropan-2-ylimino)methyl\-4-methylphen ol) with three copper(ii) salts. The available NO3-, ClO4- and CF3COO- ions have been trapped for spontaneous' anion-directed self-assembly' reactions. All the synthesized complexes contain the [Cu-2(-H(4)L1)(-OH)](2+) fragment, prone to assemble and crystallize [Cu-4] and [Cu-5] complexes under varying reaction conditions. They were characterized by UV-vis and IR spectroscopy, X-ray diffraction analysis and magnetic studies. A change from NO3- to ClO4- and CF3COO- results in different courses of reactions based on Cu-2(-H(4)L1) fragments. Binding of NO3- provided 1 as an isolated [Cu-2] complex by trapping the reactive fragment. In 2 a perchlorate ligand, in the (1,3)-binding mode, has been realized as a solitary support for the condensation of two Cu-2(-H(4)L1) fragments. The \Cu-5((3)-OH)(2)((1,3)-O2CCF3)(2)\(6+) constellation in 3 contains five Cu-II centers with a unique Z-in distorted octahedral one at the central position. Binding of different anions to the copper(ii) centers controls the nuclearity of the reaction products and tuning of the self-aggregation process within the same ligand environment (-H(4)L1(-)). The magnetic properties of the compounds have been studied both experimentally and using DFT calculations, revealing moderate to strong antiferromagnetic coupling in all aggregates.

International audience; In this manuscript we present a computational study on the photoluminescence properties of several heteroleptic [Ru(H)(CO)(N^N)(tpp)2]+ complexes (tpp = triphenylphosphine). A special focus is set on disentangling the temperature-dependent emissive properties. Experimentally, when cooling a solution of [Ru(H)(CO)(dmphen)(tpp)2]+ (dmphen = 5,6-dimethyl-1,10-phenanthroline) from room to cryogenic temperature, a partial emission switch from metal-to-ligand charge transfer (3MLCT) to ligand-centered (3LC) phosphorescence is observed, resulting in dual photoluminescence. Two different origins of the anomalous emissions are possible, i.e., thermal equilibration between electronically excited states or different excited state solvent relaxation effects. Our calculations are in favor of the thermally equilibrated scenario. This computational investigation highlights the importance of controlling the temperature-dependent emissive behavior for optoelectronic applications.

A phosphorescent cage of the form [Pd4Ru8](24+) is reported. The cage was formed using the metalloligand [Ru(dtbubpy)(2)(qpy)](2+), where qpy = 4,4': 2',2 `': 4 `',4'''-quaterpyridine and dtbubpy = 4,4'-di-tert-butyl-2,2'-bipyridine. The cage has been characterised by NMR, ESI-MS, TEM and X-ray diffraction analyses and its emission properties elucidated by steady-state and time-resolved emission spectroscopy.

In this article the biradicaloid character of the ground-state structures of N2P2R2 (R = CH3) rings is studied using the DFT and CASSCF methods, and a satisfactory agreement of the B3LYP functional and CASSCF(6,6) ab initio method has been found. In order to obtain an adequate description of the biradicaloid character, we have combined two criteria: (i) singlet–triplet energy gaps and (ii) relative values of the occupation numbers for bonding and antibonding orbitals associated with the radical sites. We have analyzed how the biradicaloid character of the N2P2R2 ring changes upon coordination to M(CO)5 (M = Cr, Mo, and W) at the B3LYP/6-311+G* level of theory. Interestingly, in some cases the biradicaloid character increases dramatically upon complexation of the N2P2R2 ligands.

The reactivitiy of tetrakis(trifluoromethyl)cyclopentadienone towards different C-based Lewis bases, such as N-heterocyclic carbenes (NHC), ylides and isonitriles, are reported. While sterically not hindered carbenes were found to yield kinetic adducts by regiospecific nucleophilic attack at the position adjacent to the carbonyl group of the ketone, bulkier nucleophiles afforded the thermodynamically more stable O-bridged zwitterions. Interestingly, isonitriles were found to dimerize and trimerize under the same reaction conditions, forming bicyclic products that evolve differently depending on the nature of the substituents.

EZ-C acknowledges the University of St Andrews and EPSRC (EP/M02105X/1) for financial support. DE thanks funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 700961. DJ acknowledges the European Research Council (grant: 278845) and the RFI Lumomat for financial support. We present dynamic supramolecular systems composed of a Ru(II) complex of the form of [Ru(dtBubpy)2(qpy)][PF6]2 (where dtBubpy is 4,4′-di-tert-butyl-2,2′-dipyridyl and qpy is 4,4':2',2'':4'',4'''-quaterpyridine) and zinc tetraphenylporphyrins (ZnTPP), through non- covalent interactions between the distal pyridine moieties of the qpy ligand the zinc of ZnTPP. The optoelectronic properties of the assemblies and the electronic interactions between the chromophoric units have been comprehensively characterized by computational investigations, and steady-state and time-resolved emission spectroscopy. Upon photoexcitation of ZnTPP, electron transfer to the ruthenium center is thermodynamically favorable and, as a result, strong emission quenching of both units occurs. Postprint

Computationally-guided blue phosphor design strategies to attain photostable complexes upon PhOLED operation., Using Ir(iii) complexes as dopants in phosphorescent organic light-emitting diodes (PhOLEDs) is the most successful strategy to attain long-lasting and highly-performant electroluminescent devices. Whilst highly efficient blue PhOLEDs are accessible, their limited operational lifetimes still restraint their practical use in lighting and displays. These short lifetimes are directly related to the low intrinsic photostability of blue Ir(iii) complexes. This work uses first principles to unveil the mechanisms of degradation of blue phosphors arising from energetically hot excited states (≅6.0 eV), and to propose a strategy for improving the stability of blue phosphors.

Cyclometalated Ir(III) complexes showing strong absorption of visible light and a long-lived triplet state are of particular interest as photocatalysts and photosensitizers. Steady-state and femtosecond transient absorption spectroscopy, complemented with TD-DFT computations, are used to study the ultrafast intersystem crossing (ISC) dynamics of two perylenebisimide (PBI)-containing cyclometalated Ir(III) complexes (Ir PBI and Ir NPBI). The S-1 -> T-n ISC dynamics of these complexes is ultrafast, similar to the conventional Ir(III) complexes bearing a (MLCT)-M-1 -> (MLCT)-M-3 transition. Much longer triplet decay lifetimes are observed in Ir PBI (tau(T) = 11.4 mu s) and Ir-NPBI (tau(T) = 7.9 mu s) compared to conventional Ir(III) complexes (tau(T) < 5 mu s). This can be rationalized by the character of the lowest -energy triplet excited state (T-1). In the case of the PBI-containing complexes, the T-1 is of intraligand character ((IL)-I-3), and the T-1 -> S-0 spin orbital coupling (SOC) is 3 cm(-1). This is in contrast with conventional Ir(III) complexes, where the (MLCT)-M-3 -> S-0 has SOCs of 490 cm(-1). In the presence of a typical sacrificial electron donor, triethanolamine (TEOA), the coordinated PBI ligands are transformed into their radical form under an inert atmosphere, either with or without photoexcitation. We found that the triplet-state population is decreased with formation of the radical. The doublet excited state has a lifetime in the range of 4-7 ps.

In this Article, we address the complexity of the emissive processes of a square-planar heteroleptic Pt(II) complex bearing 2-phenylpyridine (ppy) as cyclometalated ligand and an acetylacetonate derivative (dbm) as ancillary ligand. The origins of emission were identified with the help of density functional theory (DFT) and quadratic response (QR) time-dependent (TD)-DFT calculations including spin-orbit coupling (SOC). To unveil the photodeactivation mechanisms, we explored the triplet potential energy surfaces and computed the SOCs and the radiative decay rates (kr) from possible emissive states. We find that emission likely originates from a higher-lying (3)MLCT/(3)LLCT state and not from the Kasha-like (3)MLCT/(3)LCdbm state. The temperature-dependent nonradiative deactivation mechanisms were also elucidated. The active role of metal-centered ((3)MC) triplet excited states is confirmed for these deactivation pathways.

The biradicaloid character of the ground-state structures of N2P2 rings is studied by using the high-level ab initio multiconfigurational CASPT2/CASSCF method. In order to obtain accurate descriptors, we combine two criteria: 1) singlet-triplet energy gaps and 2) relative values of the occupation numbers for bonding and antibonding orbitals associated with the radical sites. The singlet-triplet energy gaps, the occupation numbers of antibonding-like orbitals, and the weights of the main configuration state functions (CSFs) of the ground-state wavefunctions, that is, Ψ((1)A1), are used to derive the biradicaloid character that ranges from 10-15%.

Ir(III) complexes are often used as triplet emitter dopants in phosphorescent organic light-emitting diodes (PhOLEDs). Optimizing their photoluminescence quantum yields (PLQY) at room temperature and controlling the light-outcoupling is key to attain highly performant PhOLEDs.[1] This work demonstrates that the quantum chemical modelling of phosphors is a helpful tool to: i) attain quantitative predictions of their PLQY and ii) rationalize the amount of light-outcoupling. More in details, we show that the quantitative prediction of the PLQY of blue-to-green Ir(III) complexes can be derived exclusively from electronic structure calculations and the use of simplified kinetic models.[2] Within these models, only a few calculations are needed: computing the radiative rate from the emissive state and characterizing the potential energy surfaces of the temperature-dependent non-radiative deactivation channels. This approach is extremely beneficial for the in silico prescreening of promising deep blue PhOLED emissive materials. Finally, the accurate calculation of the singlet-triplet transition dipole moments provides important insights into the design of Ir(III) complexes with improved outcoupling factors. [1] Computational insights into the photodeactivation dynamics of phosphors for OLEDs: a perspective. D. Escudero and D. Jacquemin, Dalton Trans., 2015, 44, 8346. [2] Quantitative prediction of photoluminescence quantum yields of phosphors from first principles. D. Escudero, Chem. Sci., 2016, 7, 1262.

We report the synthesis and characterization of a neutral heteroleptic Ir(III) complex bearing 6-fluoro-2-phenylbenzo[d]thiazole as cyclometalating ligand and (Z)-6-(9H-carbazol-9-yl)-5-hydroxy-2,2-dimethylhex-4-en-3-one as ancillary ligand. The photodeactivation mechanisms have been elucidated through extensive density functional theory (DFT) calculations. The active role of metal-centered ((3) MC) triplet excited states in the nonradiative deactivation pathways is, for first time, confirmed in such complexes.

Aşkun, Tülin (Balikesir Author), "A new Cu(II) dinuclear complex, Cu2L2 (1) was afforded employing the potentially pentatentate Schiff base precursor H2L, a refluxed product of o-vanillin and diethylenetriamine in methanol. Complex 1 was systematically characterized by FTIR, UV-Vis, emission and EPR spectrometry. The single crystal X-ray diffraction analysis of 1 reveals that the copper atom exhibits a distorted square planar geometry, comprising two pairs of phenolato-O and imine-N donors from two different H2L ligands. The temperature dependent magnetic interpretation agrees with the existence of weak antiferromagnetic interactions between the bridging dinuclear Cu(II) ions. A considerable body of experimental evidence has been accumulated to elucidate the magneto-structural relationship in this dinuclear Cu(II) complex by DFT computation. Both the ligand and complex 1 exhibit anti-mycobacterial activity and considerable efficacy on M. tuberculosis H37Ra (ATCC 25177) and M. tuberculosis H(37)Rv (ATCC 25618) strains. The practical applicability of the ligand and complex 1 has been examined in living cells (African Monkey Vero Cells). The MTT assay proves the non-toxicity of the probe up to 100 mg mL(-1). A new homometallic dinuclear Cu(II) complex is afforded with a tetradentate Schiff base precursor. EPR interpretation and temperature dependent magnetic studies show that complex 1 has weak antiferromagnetic coupling and DFT computation is governed to explain the magneto-structural correlation.", "Council of Scientific and Industrial Research (CSIR) New Delhi, India 01(2731)/13/ EMR-II DGICYT of Spain CTQ2014-57393-C2-1-P CSD2010-00065 "

International audience; Ten metal-based complexes and associated ligands have been synthesized and characterized. One of the metal ligands is a coumarin-phosphine derivative, which displays tunable fluorescence properties. The fluorescence is quenched in the case of the free ligand and ruthenium and osmium complexes, whereas it is strong for the gold complexes and phosphonium derivatives. These trends were rationalized by theoretical calculations, which revealed non-radiative channels involving a dark state for the free ligands that is lower in energy than the emissive state and is responsible for the quenching of fluorescence. For the Ru-II and Os-II complexes, other non-radiative channels involving the manifold of singlet and triplet excited states may play a role. The anti-proliferative properties of all the compounds were evaluated in cancer cell lines (SW480, HCT116, MDA-MB-231 and MCF-7); higher IC50 values were obtained for gold(I) complexes, with the free ligands being only weakly cytotoxic.

International audience; Isometrically dibromated thienyl-containing aza-BODIPYs CDB-1 and BDB-2 with potential use as photosensitizers (PSs) were successfully prepared and their photophysical properties were fully characterized. Singlet oxygen generation experiments were also performed. In this regard, PS CDB-1 was found to be more effective and had about two-fold rate enhancement compared to PS BDB-2. DFT and TD-DFT calculations helped to provide insights into the distinct intersystem crossing (ISC) processes observed for CDB-1 and BDB-2.

Optimizing the photoluminescence quantum yields of Ir(III) complexes is the key to their application as phosphors in organic light-emitting diodes (OLEDs). This work demonstrates for the first time that quantitative predictions of photoluminescence quantum yields (PLQY) in a series of blue-to-green Ir(III) complexes can be derived exclusively from electronic structure calculations.

Efficient intersystem crossing (ISC) in heavy-atom-free organic chromophores remains rare because of the lack of strong spin-orbit coupling effects in such compounds. Finding organic chromophores with ISC ability is important for applications in several areas, e.g., photocatalysis and photodynamic therapy. Herein, we report new perylenebisimide (PBI) chromophores with tetraphenylethynyl substituents at the 2,5,8,11-positions of the PBI core (ortho-positions, not the usually reported bay-positions of PBI), which show efficient ISC without the presence of any heavy atoms. Steady-state and picosecond-nanosecond transient absorption spectroscopies as well as time-dependent density functional theory computations were used to reveal the photophysical properties. For one of the PBI derivatives, excitation wavelength-dependent ISC was observed. The efficient ISC was attributed to the S-1/S-2 −> T-n (n > 1) processes. Photochemical reduction of the PBI derivatives in the presence of a sacrificial electron donor (triethanolamine) produced a stable PBI radical anion.

The UV visible absorption spectra of six new optical sensors based on acidochromic azobenzenes have been measured and assigned with the help of quantum chemical calculations. The investigated compounds are able to monitor the pH in the range from pH 3-10. Using the hybrid density functional PBEO and including solvent effects with a polarized continuum model, the agreement between the experimental and theoretical UV/vis spectra of the dyes in their neutral and anionic forms is very good. The spectroscopic pi pi* states, responsible for the optical properties of the sensors, are described within an accuracy of 0.1 eV. Similar accuracy is demonstrated in the ne states. The pi pi* states can be assigned as a charge transfer from the aromatic pi orbital localized in the azo-phenol moiety to the antibonding pi* of the azo group. Under basic conditions, the spectrum is bathochromically shifted and more intense than in acid media. Upon substitution in the phenyl moiety, red- or blue-shifts of the UV visible bands are observed depending on whether the substituent is electron-donor or -withdrawing, respectively. These effects are stronger at high pH values and can be rationalized in terms of the stabilization and/or destabilization of the involved frontier orbitals.

Four new cadmium(II) complexes [Cd2(bz)4(H2O)4(μ2-hmt)]·Hbz·H2O (1), [Cd3(bz)6(H2O)6(μ2-hmt)2]·6H2O (2), [Cd(pa)2(H2O)(μ2-hmt)]n (3), and {[Cd3(ac)6(H2O)3(μ3-hmt)2]·6H2O}n (4) with hexamine (hmt) and monocarboxylate ions, benzoate (bz), phenylacetate (pa), or acetate (ac) have been synthesized and characterized structurally. Structure determinations reveal that 1 is dinuclear, 2 is trinuclear, 3 is a one-dimensional (1D) infinite chain, and 4 is a two-dimensional (2D) polymer with fused hexagonal rings consisting of CdII and hmt. All the CdII atoms in the four complexes (except one CdII in 2) possess seven-coordinate pentagonal bipyramidal geometry with the various chelating bidentate carboxylate groups in equatorial sites. One of the CdII ions in 2, a complex that contains two monodentate carboxylates is in a distorted octahedral environment. The bridging mode of hmt is μ2- in complexes 1−3 but is μ3- in complex 4. In all complexes, there are significant numbers of H-bonds, C−H/π, and π−π interactions wh...

The reaction of bis(2-pyridylmethyl)amine (II) with t-butylamine and dimethylzinc gives the heteroleptic [(MeZn)2{μ-N(H)tBu}{μ-N(CH2Py)2}] (1). Stoichiometric alcoholysis of 1 with methanol leads to the exchange of the μ-N(H)tBu moiety. Almost quantitatively the corresponding methoxide [(MeZn)2(μ-OMe){μ-N(CH2Py)2}] (2) is formed. Alternatively bis(alkylzinc)methoxide-bis(2-pyridylmethyl)amides (Alkyl = methyl (2), bis(trimethylsilyl)methyl) (3)) are also accessible by direct zincation of bis(2-pyridylmethyl)amine (II) and methanol with dialkylzinc regardless of the bulkiness of the alkyl groups. Extensive DFT calculations on the alcoholysis mechanism reveal the preferential insertion of methanol into a zinc amide bond rather than the cleavage of zinc carbon bonds. An intermediate with a Zn[μ-(MeO⋯H⋯NHR)]Zn functionality is predicted. Aminolyis of 1 with t-butylamine leads to intermediates with Zn[μ-(RNH ⋯ H ⋯ NHR)]Zn functionalities, respectively. We were able to detect the latter by 1H NMR spectroscopy. The aminolysis of 1 with an excess of phenylamine results in a partial decomposition of the complex leading to the hexanuclear amide [{Zn(μ-N(H)Ph)}{MeZn(μ-N(H)Ph)}2{μ-N(CH2Py)2}]2 (4). Compound 2 is able to cleave silicon grease when dissolved in t-butylamine yielding [(MeZn)2{μ-N(CH2Py)2}2Zn{μ-(OMe2Si)2O}] (5). The X-ray structures of complexes 1–5 are discussed.

We have analyzed the non-covalent interactions observed in the Z-DNA structure by examining structures retrieved from the nucleic database (NDB) and by using high level ab initio calculations (RI-MP2/aug-cc-pVTZ). We have found interesting cooperativity effects between the non-covalent interactions involved, which are important in giving stability to the Z-DNA.

We report on the synthesis and characterization of bis-cyclometalated iridium(III) complexes with 4-phenyl-1H-[1,2,3]triazole, synthesized via a "click"-chemistry approach, as a new type of cyclometalating ligand. The photophysical and electrochemical properties of these complexes are investigated experimentally as well as theoretically by using density functional theory. The properties of these new complexes are compared to their known 2-phenylpyridinato analogues. The emission of the herein described complexes is clearly influenced by the applied ancillary ligand and can be adjusted over a broad range of frequencies. The results indicate that the phenyl-1H-[1,2,3]triazole ligands in general cause a spectral blue shift.

A Cu-II complex of protonated 4,4'-bipyridine (Hbyp) and 2-picolinate (pic), [Cu-2(pic)(3)(Hbyp)(H2O)(ClO4)(2)], has been synthesised and characterised by single-crystal X-ray analysis. The structure consists of two copper atoms that have different environments, bridged by a carboxylate group. The equatorial plane is formed by the two bidentate picolinate groups in one Cu-II, and one picolinate, one monodentate 4,4'-bipyridyl ligand and a water molecule in the other. Each copper atom is also weakly bonded to a perchlorate anion in an axial position. One of the coordinated perchlorate groups displays anion-pi interaction with the coordinated pyridine ring. The noncoordinated carboxylate oxygen is involved in lone-pair (l.p.)-pi interaction with the protonated pyridine ring. In addition there are pi-pi and H-bonding interactions in the structure. Bader's theory of "atoms in molecules" (AIM) is used to characterise the anion-pi and l.p.-pi interactions observed in the solid state. A high-level ab initio study (RI-MP2/aug-cc-pVTZ level of theory) has been performed to analyse the anion-pi binding affinity of the pyridine ring when it is coordinated to a transition metal and also when the other pyridine ring of the 4,4'-bipyridine moiety is protonated. Theoretical investigations support the experimental findings of an intricate network of intermolecular interactions, which is characterised in the studied complex, and also indicate that protonation as well as coordination to the transition metal have important roles in influencing the pi-binding properties of the aromatic ring. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

The interplay among three important non-covalent interactions involving aromatic rings is studied by means of ab initio calculations (RI-MP2/aug-cc-pVTZ//RI-MP2/aug-cc-pVDZ, and RI-MP2/CBS levels of theory). They demonstrate that synergetic effects are present in complexes where hydrogen bonding interactions, cation–π, and π–π interactions coexist. These synergetic effects have been studied using the genuine non-additivity energies and the molecular interaction potential with polarization partition scheme.