Study of the Photophysical Properties and the DNA Binding of Enantiopure [Cr(TMP)(dppn)] Complex.

The preparation, electrochemistry and photophysical properties of a heteroleptic chromium(III) polypyridyl complex [Cr(TMP)(dppn)] () containing two 3,4,7,8-tetramethyl-1,10-phenanthroline (TMP) ligands and the π-extended benzodipyrido[3,2-a:2',3'-]phenazine (dppn) ligand are reported. The visible absorption spectrum of reveals distinct bands between 320 and 420 nm characteristic of dppn-based ligand-centered transitions, with found to be nonemissive in aqueous solution but weakly luminescent in aerated acetonitrile solution. Transient visible absorption (TrA) spectroscopy reveals that 400 nm excitation of leads to initial population of a ligand-to-metal charge transfer (LMCT) state which evolves within tens of ps to form a dppn-localized intraligand (IL) state which persists for longer than 7 ns and efficiently sensitizes singlet oxygen.

Prediction and Rationalization of Different Photochemical Behaviors of - and -Isomers of [Ru(pyridyltriazole)].

Facial and meridional isomerism of metal complexes is known to result in fundamental differences in photophysical properties. One may also envisage differences in their photochemical reactivity and therefore predict different outcomes of their light-triggered transformations. The - and -isomers of the complex [Ru(pytz)] (- & -, pytz = 1-benzyl-4-(pyrid-2-yl)-1,2,3-triazole) were separated and isolated.

Photochemistry of Ru(II) Triazole Complexes with 6-Membered Chelate Ligands: Detection and Reactivity of Ligand-Loss Intermediates.

Photochemical ligand release from metal complexes may be exploited in the development of novel photoactivated chemotherapy agents for the treatment of cancer and other diseases. Highly intriguing photochemical behavior is reported for two ruthenium(II) complexes bearing conformationally flexible 1,2,3-triazole-based ligands incorporating a methylene spacer to form 6-membered chelate rings. [Ru(bpy)(pictz)] () and [Ru(bpy)(btzm)] () (bpy = 2,2'-bipyridyl; pictz = 1-(picolyl)-4-phenyl-1,2,3-triazole; btzm = bis(4-phenyl-1,2,3-triazol-4-yl)methane) exhibit coordination by the triazole ring through the less basic N2 atom as a consequence of chelation and readily undergo photochemical release of the pictz and btzm ligands (ϕ = 0.

A Near-Infrared Luminescent Cr(III) -Heterocyclic Carbene Complex.

Photoluminescent coordination complexes of Cr(III) are of interest as near-infrared spin-flip emitters. Here, we explore the preparation, electrochemistry, and photophysical properties of the first two examples of homoleptic -heterocyclic carbene complexes of Cr(III), featuring 2,6-(imidazolyl)pyridine (ImPyIm) and 2-imidazolylpyridine (ImPy) ligands. The complex [Cr(ImPy)] displays luminescence at 803 nm on the microsecond time scale (13.

A stronger acceptor decreases the rates of charge transfer: ultrafast dynamics and on/off switching of charge separation in organometallic donor-bridge-acceptor systems.

To unravel the role of driving force and structural changes in directing the photoinduced pathways in donor-bridge-acceptor (DBA) systems, we compared the ultrafast dynamics in novel DBAs which share a phenothiazine (PTZ) electron donor and a Pt(ii) -acetylide bridge (-C[triple bond, length as m-dash]C-Pt-C[triple bond, length as m-dash]C-), but bear different acceptors conjugated into the bridge (naphthalene-diimide, NDI; or naphthalene-monoimide, NAP). The excited state dynamics were elucidated by transient absorption, time-resolved infrared (TRIR, directly following electron density changes on the bridge/acceptor), and broadband fluorescence-upconversion (FLUP, directly following sub-picosecond intersystem crossing) spectroscopies, supported by TDDFT calculations. Direct conjugation of a strong acceptor into the bridge leads to switching of the lowest excited state from the intraligand IL state to the desired charge-separated CSS state.

Direct Determination of the Rate of Intersystem Crossing in a Near-IR Luminescent Cr(III) Triazolyl Complex.

A detailed understanding of the dynamics of photoinduced processes occurring in the electronic excited state is essential in informing the rational design of photoactive transition-metal complexes. Here, the rate of intersystem crossing in a Cr(III)-centered spin-flip emitter is directly determined through the use of ultrafast broadband fluorescence upconversion spectroscopy (FLUPS). In this contribution, we combine 1,2,3-triazole-based ligands with a Cr(III) center and report the solution-stable complex [Cr(btmp)] (btmp = 2,6-(4-phenyl-1,2,3-triazol-1-yl-methyl)pyridine) (), which displays near-infrared (NIR) luminescence at 760 nm (τ = 13.

Not All MC States Are the Same: The Role of MC States in the Photochemical NN Ligand Release from [Ru(bpy)(NN)] Complexes.

Ruthenium(II) complexes feature prominently in the development of agents for photoactivated chemotherapy; however, the excited-state mechanisms by which photochemical ligand release operates remain unclear. We report here a systematic experimental and computational study of a series of complexes [Ru(bpy)(NN)] (bpy = 2,2'-bipyridyl; NN = bpy (), 6-methyl-2,2'-bipyridyl (), 6,6'-dimethyl-2,2'-bipyridyl (), 1-benzyl-4-(pyrid-2-yl)-1,2,3-triazole (), 1-benzyl-4-(6-methylpyrid-2-yl)-1,2,3-triazole (), 1,1'-dibenzyl-4,4'-bi-1,2,3-triazolyl ()), in which we probe the contribution to the promotion of photochemical NN ligand release of the introduction of sterically encumbering methyl substituents and the electronic effect of replacement of pyridine by 1,2,3-triazole donors in the NN ligand. Complexes to all release the ligand NN on irradiation in acetonitrile solution to yield [Ru(bpy)(NCMe)], with resultant photorelease quantum yields that at first seem counter-intuitive and span a broad range.

G-Quadruplex Binding of an NIR Emitting Osmium Polypyridyl Probe Revealed by Solution NMR and Time-Resolved Infrared Studies.

G-quadruplexes are emerging targets in cancer research and understanding how diagnostic probes bind to DNA G-quadruplexes in solution is critical to the development of new molecular tools. In this study the binding of an enantiopure NIR emitting [Os(TAP) (dppz)] complex to different G-quadruplex structures formed by human telomer (hTel) and cMYC sequences in solution is reported. The combination of NMR and time-resolved infrared spectroscopic techniques reveals the sensitivity of the emission response to subtle changes in the binding environment of the complex.

Photophysical Properties and DNA Binding of Two Intercalating Osmium Polypyridyl Complexes Showing Light-Switch Effects.

The synthesis and photophysical characterization of two osmium(II) polypyridyl complexes, [Os(TAP)dppz] () and [Os(TAP)dppp2] () containing dppz (dipyrido[3,2-:2',3'-]phenazine) and dppp2 (pyrido[2',3':5,6]pyrazino[2,3-][1,10]phenanthroline) intercalating ligands and TAP (1,4,5,8-tetraazaphenanthrene) ancillary ligands, are reported. The complexes exhibit complex electrochemistry with five distinct reductive redox couples, the first of which is assigned to a TAP-based process. The complexes emit in the near-IR ( at 761 nm and at 740 nm) with lifetimes of >35 ns with a low quantum yield of luminescence in aqueous solution (∼0.

Synthesis and characterisation of group 8 tris(1-benzyl-1,2,3-triazol-4-yl)--anisolylmethane complexes.

The tris(1,2,3-triazol-4-yl)methane framework offers a highly versatile architecture for ligand design, yet the coordination chemistry of this class of ligand remains largely unexplored. We report here the synthesis and characterisation of the homoleptic complexes [M(ttzm)](PF) (ttzm = tris(1-benzyl-1,2,3-triazol-4-yl)--anisolylmethane; M = Fe (), Ru (), Os ()). Initial attempts to prepare by reaction of [Ru(-cymene)Cl] and ttzm also led to the isolation of the heteroleptic complex [Ru(-cymene)(ttzm)](PF).

Photochemistry of Heteroleptic 1,4,5,8-Tetraazaphenanthrene- and Bi-1,2,3-triazolyl-Containing Ruthenium(II) Complexes.

Diimine metal complexes have significant relevance in the development of photodynamic therapy (PDT) and photoactivated chemotherapy (PACT) applications. In particular, complexes of the TAP ligand (1,4,5,8-tetraazaphenanthrene) are known to lead to photoinduced oxidation of DNA, while TAP- and triazole-based complexes are also known to undergo photochemical ligand release processes relevant to PACT. The photophysical and photochemical properties of heteroleptic complexes [Ru(TAP)(btz)] (btz = 1,1'-dibenzyl-4,4'-bi-1,2,3-triazolyl, = 1 (), 2 ()) have been explored.

Triazole-based osmium(ii) complexes displaying red/near-IR luminescence: antimicrobial activity and super-resolution imaging.

Cellular uptake, luminescence imaging and antimicrobial activity against clinically relevant methicillin-resistant (MRSA) bacteria are reported. The osmium(ii) complexes [Os(^)] (^ = 1-benzyl-4-(pyrid-2-yl)-1,2,3-triazole ( ); 1-benzyl-4-(pyrimidin-2-yl)-1,2,3-triazole ( ); 1-benzyl-4-(pyrazin-2-yl)-1,2,3-triazole ( )) were prepared and isolated as the chloride salts of their meridional and facial isomers. The complexes display prominent spin-forbidden ground state to triplet metal-to-ligand charge transfer (MLCT) state absorption bands enabling excitation as low as 600 nm for /- and observation of emission in aqueous solution in the deep-red/near-IR regions of the spectrum.

Quenching of the phosphorescence of thermally reversible photochromic naphthopyran Re(i) complexes initiated by either visible or ultraviolet radiation.

Re(i) complexes bearing thermally reversible photochromic naphthopyran axial ligands undergo highly efficient, reversible phosphorescence quenching actuated by either visible or UV irradiation. The photoinduced quenching of the triplet metal-to-ligand charge-transfer (MLCT) emission is interpreted based on changes in the relative energies of the excited states.

Unravelling the Mechanism of Excited-State Interligand Energy Transfer and the Engineering of Dual Emission in [Ir(CN)(NN)] Complexes.

Fundamental insights into the mechanism of triplet-excited-state interligand energy transfer dynamics and the origin of dual emission for phosphorescent iridium(III) complexes are presented. The complexes [Ir(CN)(NN)] (HCN = 2-phenylpyridine (-), 2-(2,4-difluorophenyl)pyridine (-), 1-benzyl-4-phenyl-1,2,3-triazole (-); NN = 1-benzyl-4-(pyrid-2-yl)-1,2,3-triazole (pytz, ), 1-benzyl-4-(pyrimidin-2-yl)-1,2,3-triazole (pymtz, ), 1-benzyl-4-(pyrazin-2-yl)-1,2,3-triazole (pyztz, )) are phosphorescent in room-temperature fluid solutions from triplet metal-to-ligand charge transfer (MLCT) states admixed with either ligand-centered (LC) (, , and ) or ligand-to-ligand charge transfer (LL'CT) character (, , and -). Particularly striking is the observation that pyrimidine-based complex exhibits dual emission from both MLCT/LC and MLCT/LL'CT states.

Observation of an Inversion in Photophysical Tuning in a Systematic Study of Luminescent Triazole-Based Osmium(II) Complexes.

In a systematic survey of luminescent bis(terdentate) osmium(II) complexes, a tipping point involving a reversal in photophysical tuning is observed whereby increasing stabilization of the ligand-based lowest unoccupied molecular orbital (LUMO) results in a blue shift in the optical absorption and emission bands. The complexes [Os(N^N'^N″)] [N^N'^N″ = 2,6-bis(1-phenyl-1,2,3-triazol-4-yl)pyridine (Os1), 2,6-bis(1-benzyl-1,2,3-triazol-4-yl)pyrazine (Os2), 6-(1-benzyl-1,2,3-triazol-4-yl)-2,2'-bipyridyl (Os3), 2-(pyrid-2-yl)-6-(1-benzyl-1,2,3-triazol-4-yl)pyrazine (Os4), 2-(pyrazin-2-yl)-6-(1-benzyl-1,2,3-triazol-4-yl)pyridine (Os5), and 6-(1-benzyl-1,2,3-triazol-4-yl)-2,2'-bipyrazinyl (Os6)] have been prepared and characterized, and all complexes display phosphorescence ranging from the orange to near-IR regions of the spectrum. Replacement of the central pyridine in the ligands of Os1 by the more π-accepting pyrazine in Os2 results in a 55 nm red shift in the triplet metal-to-ligand charge-transfer-based emission band, while a larger red shift of 107 nm is observed for the replacement of one of the triazole donors in the ligands of Os1 by a second pyridine ring in Os3 (λ = 702 nm).

Photophysical and Cellular Imaging Studies of Brightly Luminescent Osmium(II) Pyridyltriazole Complexes.

The series of complexes [Os(bpy)(pytz) ][PF] (bpy = 2,2'-bipyridyl, pytz = 1-benzyl-4-(pyrid-2-yl)-1,2,3-triazole, 1 n = 0, 2 n = 1, 3 n = 2, 4 n = 3) were prepared and characterized and are rare examples of luminescent 1,2,3-triazole-based osmium(II) complexes. For 3 we present an attractive and particularly mild preparative route via an osmium(II) η-arene precursor circumventing the harsh conditions that are usually required. Because of the high spin-orbit coupling constant associated with the Os(II) center the absorption spectra of the complexes all display absorption bands of appreciable intensity in the range of 500-700 nm corresponding to spin-forbidden ground-state-to-MLCT transitions (MLCT = metal-to-ligand charge transfer), which occur at significantly lower energies than the corresponding spin-allowed MLCT transitions.

Mitochondria-localising DNA-binding biscyclometalated phenyltriazole iridium(iii) dipyridophenazene complexes: syntheses and cellular imaging properties.

Two new biscyclometalated complexes [Ir(ptzR)2(dppz)]+ (dppz = dipyridophenazene; ptzRH = 4-phenyl-1-benzyl-1,2,3-triazole (1+) and 4-phenyl-1-propyl-1,2,3-triazole (2+)) have been prepared. The hexafluorophosphate salts of these complexes have been fully characterized and, in one case, the X-ray structure of a nitrate salt was obtained. The DNA binding properties of the chloride salts of the complexes were investigated, as well as their cellular uptake by A2780 and MCF7 cell lines.

An unexpected journey from highly tunable phosphorescence to novel photochemistry of 1,2,3-triazole-based complexes.

The photophysical properties of transition metal complexes have long attracted interest in the literature with significant research activity during the past two to three decades due to the potential exploitation of these materials in solar energy conversion, light-emitting technology, luminescence biological imaging and photodynamic therapeutic applications to name but a few. Since the advent of the facile preparation of 1,2,3-triazole-based compounds through copper(i)-catalysed cycloaddition, ligands based on this heterocycle have received widespread attention in coordination chemistry. Inevitably, their ability to be used as pyridine-like analogues has resulted in significant attention on the photophysical properties of their resultant complexes.

Towards Water Soluble Mitochondria-Targeting Theranostic Osmium(II) Triazole-Based Complexes.

The complex [Os(btzpy)₂][PF₆]₂ (, btzpy = 2,6-bis(1-phenyl-1,2,3-triazol-4-yl)pyridine) has been prepared and characterised. Complex exhibits phosphorescence (λ = 595 nm, τ = 937 ns, φ = 9.3% in degassed acetonitrile) in contrast to its known ruthenium(II) analogue, which is non-emissive at room temperature.

Stabilising the lowest energy charge-separated state in a {metal chromophore - fullerene} assembly: a tuneable panchromatic absorbing donor-acceptor triad.

Photoreduction of fullerene and the consequent stabilisation of a charge-separated state in a donor-acceptor assembly have been achieved, overcoming the common problem of a fullerene-based triplet state being an energy sink that prevents charge-separation. A route to incorporate a C-fullerene electron acceptor moiety into a catecholate-Pt(ii)-diimine photoactive dyad, which contains an unusually strong electron donor, 3,5-di--butylcatecholate, has been developed. The synthetic methodology is based on the formation of the aldehyde functionalised bipyridine-Pt(ii)-3,5-di--butylcatechol dyad which is then added to the fullerene cage a Prato cycloaddition reaction.

Labilizing the Photoinert: Extraordinarily Facile Photochemical Ligand Ejection in an [Os(N^N)3 ](2+) Complex.

Whilst [Os(N^N)3 ](2+) complexes are supposed to be photochemically inert to ligand loss, the complex [Os(btz)3 ](2+) (btz=1,1'-dibenzyl-4,4'-bi-1,2,3-triazolyl) undergoes unprecedented photolytic reactivity to liberate free btz (Φ363 ≈1.2 %). Further, both cis and trans isomers of the photodechelated ligand-loss solvento intermediate [Os(κ(2) -btz)2 (κ(1) -btz)(NCMe)](2+) are unambiguously observed and characterized by NMR spectroscopy and mass spectrometry.

Photochemistry of [Ru(pytz)(btz)2](2+) and Characterization of a κ(1)-btz Ligand-Loss Intermediate.

We report the synthesis, characterization, and photochemical reactivity of the triazole-containing complex [Ru(pytz)(btz)2](2+) (1, pytz = 1-benzyl-4-(pyrid-2-yl)-1,2,3-triazole, btz = 1,1'-dibenzyl-4,4'-bi-1,2,3-triazolyl). The UV-vis absorption spectrum of 1 exhibits pytz- and btz-centered (1)MLCT bands at 365 and 300 nm, respectively. Upon photoexcitation, acetonitrile solutions of 1 undergo conversion to the ligand-loss intermediate, trans-[Ru(pytz)(κ(2)-btz)(κ(1)-btz)(NCMe)](2+) (2, Φ363 = 0.

Luminescent osmium(ii) bi-1,2,3-triazol-4-yl complexes: photophysical characterisation and application in light-emitting electrochemical cells.

The series of osmium(ii) complexes [Os(bpy)3-n(btz)n][PF6]2 (bpy = 2,2'-bipyridyl, btz = 1,1'-dibenzyl-4,4'-bi-1,2,3-triazolyl, n = 0, n = 1, n = 2, n = 3), have been prepared and characterised. The progressive replacement of bpy by btz leads to blue-shifted UV-visible electronic absorption spectra, indicative of btz perturbation of the successively destabilised bpy-centred LUMO. For , a dramatic blue-shift relative to the absorption profile for is observed, indicative of the much higher energy LUMO of the btz ligand over that of bpy, mirroring previously reported data on analogous ruthenium(ii) complexes.

Ultrafast charge transfer dynamics in supramolecular Pt(II) donor-bridge-acceptor assemblies: the effect of vibronic coupling.

Thanks to major advances in laser technologies, recent investigations of the ultrafast coupling of nuclear and electronic degrees of freedom (vibronic coupling) have revealed that such coupling plays a crucial role in a wide range of photoinduced reactions in condensed phase supramolecular systems. This paper investigates several new donor-bridge-acceptor charge-transfer molecular assemblies built on a trans-Pt(II) acetylide core. We also investigate how targeted vibrational excitation with low-energy IR light post electronic excitation can perturb vibronic coupling and affect the efficiency of electron transfer (ET) in solution phase.

On the mechanism of vibrational control of light-induced charge transfer in donor-bridge-acceptor assemblies.

Nuclear-electronic (vibronic) coupling is increasingly recognized as a mechanism of major importance in controlling the light-induced function of molecular systems. It was recently shown that infrared light excitation of intramolecular vibrations can radically change the efficiency of electron transfer, a fundamental chemical process. We now extend and generalize the understanding of this phenomenon by probing and perturbing vibronic coupling in several molecules in solution.