Photophysical Properties Of Complexes Research Articles

Twisted Intramolecular Charge Transfer‐Based Fluorometric Detection of D‐fructose by Boronic Acid‐Containing BF2‐β‐Diketonate Complexes

AbstractNovel BF2‐β‐diketonate complexes 1–4 bearing phenylboronic acid moieties and methoxyphenyl or dimethylaminophenyl groups were synthesized and their photophysical properties, pH response, and reactivity to D‐fructose were evaluated. Complexes 1 and 2 bearing a methoxyphenyl group luminesced with high intensity in a range of non‐polar to polar solvents, except in DMSO, whereas complexes 3 and 4 containing a dimethylaminophenyl group with twisted intramolecular charge transfer (TICT) properties showed a dramatic decrease in luminescence intensity with increasing solvent polarity. The luminescence intensity of complexes 1 and 2 decreased with increasing pH due to intermolecular vibration which associated with hydrogen bonding between the complexes and solvent water molecules, whereas it increased when they reacted with D‐fructose due to the suppression of the intermolecular vibration. In contrast, the luminescence intensity of complexes 3 and 4 increased with increasing pH and upon reaction with D‐fructose due to the loss of its TICT properties. The photophysical properties of complexes 1–4 and the TICT properties of complexes 3 and 4 were supported by density functional theory calculations.

An unusual disulfide-linked dimerization in the fluorescent protein rsCherryRev1.4.

rsCherryRev1.4 has been reported as one of the reversibly photoswitchable variants of mCherry, and is an improved version with a faster off-switching speed and lower switching fatigue at high light intensities than its precursor rsCherryRev. However, rsCherryRev1.4 still has some limitations such as a tendency to dimerize as well as complex photophysical properties. Here, the crystal structure of rsCherryRev1.4 was determined at a resolution of 2 Å and it was discovered that it forms a dimer that shows disulfide bonding between the protomers. Mutagenesis, gel electrophoresis and size-exclusion chromatography strongly implicate Cys24 in this process. Replacing Cys24 in rsCherryRev1.4 resulted in a much lower tendency towards dimerization, while introducing Cys24 into mCherry correspondingly increased its dimerization. In principle, this finding opens the possibility of developing redox sensors based on controlled dimerization via disulfide cross-linking in fluorescent proteins, even though the actual application of engineering such sensors still requires additional research.

Unexpected reactivity of cyclometalated iridium(III) dimers. Direct synthesis of a mononuclear luminescent complex.

A new synthetic method has been developed for the preparation of unexpected emissive iridium(III) complexes (A and B), directly obtained from the established [Ir(ppy)2(μ-Cl)]2 dimer, under reaction conditions in which such compounds are usually considered stable. Complex A ([Ir(ppy)2(Oppy)], where Hppy = 2-phenylpyridine and HOppy = 2-(o-hydroxyphenyl)pyridine) was obtained from the dimer without the addition of further ancillary ligands in the reaction environment, but in the presence of a basic water environment in 2-ethoxyethanol as solvent at 165 °C. The complex evidences the unexpected insertion of an oxygen atom between the iridium(III) center and the carbon atom of one ppy moiety. Under specific reaction conditions, the mer-[Ir(ppy)3] complex (B) was obtained. The presence of the right amount of water is important to maximize the formation of A relative to B. Both compounds were fully characterized by NMR spectroscopy and mass spectrometry (MS), and the X-ray structure of A was also determined. DFT calculations were used to shed light on the reaction mechanism leading to the unexpected formation of A, suggesting that the Oppy ligand is generated intramolecularly once the [Ir(ppy)2(μ-OH)]2 dimer is formed. The process is probably assisted by a redox reaction involving the second iridium(III) center in the dimer. The electrochemical and photophysical properties of complexes A and B were investigated in comparison with the well-known fac-[Ir(ppy)3] analogue (C). Complex A displays a green emission (λmax = 545 nm) with a photoluminescence quantum yield (PLQY) of nearly 40%, whereas the oxygen-free counterpart B is poorly emissive, exhibiting an orange emission (λmax = 605 nm) with a PLQY below 10%. These findings may pave the way for the direct synthesis of neutral luminescent complexes with the general formula [Ir(C^N)2(OC^N)], even using dimers with non-commercial or highly substituted C^N ligands, without the need for synthesizing the corresponding hydroxyl-substituted ancillary ligand, which may be hardly obtainable.

Stability of retinol in liposomes as measured by fluorescence lifetime spectroscopy and FLIM

Retinol shows complex photophysical properties that make it potentially useful as an exogenous or endogenous probe of membrane microenvironment, but it has not been fully explored. In this study, we use bulk fluorescence lifetime measurements and fluorescence lifetime imaging microscopy (FLIM) to examine the stability of retinol in phosphatidylcholine (PC) multilamellar and unilamellar vesicles with and without cholesterol. We find that both light and exposure to ambient temperature and oxygen contribute to retinol degradation, with the addition of an antioxidant such as butylated hydroxytoluene (BHT) essential to provide stability, especially in the absence of cholesterol. With exposure to ultraviolet light to excite its native fluorescence, retinol degrades rapidly and can photosensitize vesicles. Degradation can be measured by a decrease in fluorescence lifetime. In POPC vesicles without cholesterol, BHT leads to initially higher lifetimes compared with no BHT, but it increases the rate of photodegradation. The presence of 10 mol % cholesterol protects against this effect, and vesicles with 20 mol % cholesterol show longer lifetimes without BHT under all conditions. Because of its environmental sensitivity, retinol is interesting as a FLIM probe, but careful controls are needed to avoid degradation, and additional work is needed to optimize liposomes for food and cosmetic applications.

One-Center and Two-Center Self-Trapped Excitons in Zero-Dimensional Hybrid Copper Halides: Tricolor Luminescence with High Quantum Yields.

The organic-inorganic hybrid copper halides exhibit intriguing and complex photophysical properties, and the underlying mechanisms are far from clear. Here, we study the photodynamics of six novel types of low-dimensional hybrid copper halides, which have a maximum quantum yield of 98.6%. They exhibit two origins of photon emission with distinct temperature dependence and quantum transition rates. The experiments in junction with first-principles calculations indicate that they stem from two kinds of self-trapped excitons (STEs): one-center a-STE (localized on Cu+ monomer) and two-center m-STE (localized on Cu22+ dimer). There is phase transition between a-STE and m-STE when enough thermal energy is acquired for crossing the potential barrier between them. The degree of softness of the compositional organic cations of the copper halide plays a key role in determining the self-trapping type of the STEs.

Selective formation of dinuclear and heptanuclear Zn(II), Ni(II), and Co(II) metal clusters from a simple dialdehyde

Herein, the selective formation of dinuclear and hexagonal disk-shape heptanuclear metal cluster complexes is reported. The reaction of 4-tert-butyl-2,6-diformylphenol (L) and M(ClO4)2, where M is Zn (II), Co (II), or Ni (II), in the presence of a strong base resulted in the formation of heptanuclear metal cluster complexes. Treatment of M(ClO4)2·6H2O (M = Zn, and Ni) in the presence of NaOCH3 in MeOH at the elevated temperature afforded [Zn2(L)2(CH3O)4].ClO4 (1) and [Ni2(L)2(CH3O)2].ClO4 (2). Furthermore, treatment of M(ClO4)2·6H2O (M = Zn, Co, and Ni) in the presence of NaOH in MeOH at the elevated temperature yielded heptanuclear metal cluster complexes [Zn7(L)6(µ3-CH3O)6]·2ClO4 (3), [Co7(L)6(µ3-CH3O)6]·2ClO4 (4), and [Ni7(L)6(µ3-OH)6]·2ClO4 (5). These were characterized using elemental analysis, infrared spectroscopy, and X-ray crystallography. Zinc complexes 1 and 3 were also characterized using 1H NMR spectroscopy. In the crystal structures of heptanuclear cluster complexes 3–5, six ligand molecules were aligned to hold six metal centers that were in hexagonal positions. The central metal atom was connected by the bridging of the oxygen atom of methoxy and hydroxy groups with the remaining metal atoms. The photophysical properties of complexes were studied and zinc complexes 1 and 3 showed strong fluorescence in PL spectra. Themetal cluster complexes 1, 3 and 4 were employed as catalysts in the cycloaddition reaction of CO2 to epoxide, exhibiting moderate activities.

Investigation on the photophysical properties of Cu(I) complexes supported by N‐heterocyclic carbene ligands with electron‐donating/withdrawing groups on imidazolylidene unit

AbstractTwo new four‐coordinate Cu(I) complexes consisted of bidentate NHC ligand and diphosphine ligand were successfully synthesized and characterized. The electron‐donating methyl and electron‐withdrawing chlorine groups were introduced into the imidazolylidene unit of N‐heterocyclic carbene (NHC) ligands to investigate their influences on the photophysical properties of complexes. The red‐shifted low‐energy absorption bands indicate that both methyl and chlorine decreased the band gaps between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). Theoretical calculation results show the methyl group raised the energy level of HOMO more than that of LUMO, while the chlorine substituent lowered the energy level of LUMO more than that of HOMO. Both these Cu(I) complexes show high emission efficiencies and microsecond‐scale emission lifetimes. The photophysical data at 77 K show that emissions of these complexes are the mixture of phosphorescence and thermally activated delayed fluorescence (TADF).

Complex Photophysical Properties of K114 Make for a Versatile Fluorescent Probe for Amyloid Detection.

Protein aggregation is a hallmark of Alzheimer's disease (AD) and many other neurodegenerative disorders. Small organic fluorophores such as Congo Red preferentially bind to cross-β-sheet-rich deposits and have been used to label amyloid plaques and tau tangles in histological samples. However, distinguishing between different conformations of protein aggregates is not trivial. Using silkworm and spider silks (prototypical amyloids) and transgenic AD mouse (5XFAD) and human AD brain samples, we report how spectral confocal microscopy allowed for improved detection and differentiation of protein aggregates based on the unexpected photophysical behavior of the amyloid-specific dye K114. The pH and excitation power had pronounced effects on the emission spectrum and intensity of amyloid-bound K114 fluorescence. When bound to β-sheet-rich assemblies, the emission spectrum of K114 was governed by the local pH of the binding pockets much more than by the pH of the mounting medium, likely due to ionization of titratable phenols. Unexpectedly, exposure to high excitation power caused a permanent increase in fluorescence intensity and a spectral blue-shift. These light-induced fluorescence changes were dependent in a complex manner on laser power, exposure time, pH, and amyloid type examined. The above-mentioned phenomena were observed in silk fibers and Alzheimer brain sections from mouse and human, indicating that this may be a general characteristic of K114 when bound to tightly aggregated macromolecules. Potential mechanisms are discussed, likely involving photoinduced electron transfer. Our findings illustrate how the complex photophysical behavior of amyloid-bound K114 can be exploited for improved detection and differentiation of protein aggregates.

Mononuclear gold(I) acetylide complexes with carbonyl moiety: Synthesis, characterization, and tunable emission energy

A series of gold(I) acetylide complexes, Cy3PAuCCC6H4-C(O)R-4 (RH (1), Me (2), OMe (3), NH2 (4)) (Cy3P = tricyclohexylphosphine), have been synthesized and characterized. The crystal structures of Cy3PAuCCC6H4-C(O)H-4 (1) and Cy3PAuCCC6H4-C(O)NH2-4 (4) were determined by X-ray diffraction. The photophysical properties of complexes 1–4 have been studied. Complexes 1–4 show luminescence both in the solid state and in acetonitrile solution at 298 K, and their emission energies are in the order: 4 > 3 > 2 > 1.

Benzo[4,5]thiazolo[3,2- c][1,3,5,2]oxadiazaborinines: Synthesis, Structural, and Photophysical Properties.

A family of highly emissive benzo[4,5]thiazolo[3,2- c][1,3,5,2]oxadiazaborinines, conjugated with the donor 4-dimethylaminophenyl group, was designed and synthesized. Their photophysical, both in solution and in the solid state, and structural properties were investigated. The influence of donor and acceptor substituents (R) in the benzothiazole unit on photophysical properties of complexes was found out. The tetrafluorobenzothiazole analogue exhibits nonbonded nuclear spin-spin coupling between fluorines from the BF2 group and α-fluorine atom at the benzene ring. Additionally, this boron complex demonstrates a comparatively high solid-state fluorescence quantum yield (Φ = 0.34).

Three microporous Zn coordination polymers constructed by 3,4,5-tris(carboxymethoxy)benzoic acid and 4,4′-bipyrdine: Structures, topologies, and luminescence

Three microporous Zn coordination polymers, [Zn3(OH)2(TCBA)(4,4′-bpy)]·5.5H2O (1), [Zn3(OH)2(TCBA)(4,4′-bpy)1.5]·5H2O (2), and [Zn4(TCBA)2(4,4′-bpy)2(H2O)8]·11H2O (3) (H4TCBA = 3,4,5-tris(carboxymethoxy)benzoic acid, 4,4′-bpy = 4,4′-bipyrdine), have been hydrothermally synthesized and structurally characterized. 1 presents an uncommon 2-nodal (4,10)-connected network with {3·45}2{34·412·510·614·73·82} topology; 2 can be described as a 2-nodal (3,8)-connected tfz-d net with the symbol of {43}2{46·618·84}, both networks are constructed from hexameric [Zn6(µ3-OH)4]8+ clusters. While 3 shows an interesting 4-nodal (3,3,3,4)-connected network with {8·10·12}2{8·102}2{84·10·12} topology. Complexes 1–3 all own 3-D frameworks with 1-D channels, and in 1–3 lattice and/or coordinated water molecules occupy the channels, especially in 3 Zn-bipy chains reside in the channels together with water molecules. Double helical chains can be observed in complex 2; and single helix chains exist in complexes 1 and 3. Furthermore, the thermal stabilities and photophysical properties of complexes 1–3 were also investigated.

Synthesis and optoelectronic properties of an electrically stimulated phosphorescent iridium complex

In order to better describe and verify the mechanism of electrophosphor discoloration, an ionic iridium complex with different counterions is designed and synthesized. It is found that the luminescent properties of the phosphor not only show the concentration and acid / base induced phosphorescence, but also show the phosphorescence change induced by electrical stimulation. The hydrogen bond acceptor (-NH) is introduced into the ionic iridium complex to modulate the emission wavelength of the complex by different counterions. In order to further control the emission wavelength of the complexes, a series of ionic iridium complexes with different counterions are designed and synthesized by selecting the auxiliary ligands containing two hydrogen bond acceptors (-NH). It is proved that there is not only electrostatic interaction between the cations and counterions, but also interesting hydrogen bonds. In addition, because the hydrogen bond strength formed by complex anions and different counter anions is different, it can effectively control the photophysical properties of complexes and adjust the emission wavelength from 493 nm to 591 nm. In conclusion, the phosphorescence change induced by electric field can be realized by applying the electric field to change the hydrogen bonding intensity. At the same time, the construction of quasi solid-state information storage devices is beneficial to the development of phosphorescent materials in information optoelectronic devices.

Synthesis, structural characterization and biological properties of phosphorescent iridium(III) complexes

Two phosphorescent cyclometalated iridium(III)-triptycenyl-1,10-phenanthroline complexes [Ir(ppy)2(tpt-phen)]+ (1) and [Ir(bhq)2(tpt-phen)]+ (2) {ppy=2-phenylpyridine, bhq=Benzo[h]quinoline, tpt-phen=triptycenyl-1,10-phenanthroline} have been synthesized and structurally characterized. The structure of complex 2 has been studied by single crystal X-ray crystallography. The photophysical properties of complexes in a different solvent have also been investigated. The binding of complexes to the double stranded calf thymus (CT-DNA) has been investigated by spectroscopic techniques. These complexes condense originally circular plasmid DNA into particulate structures. The DNA-condensation induced by these complexes have been investigated by electrophoretic mobilty shift assay, dynamic light scattering, and fluorescence microscopy. Furthermore, the cytotoxicity of these complexes towards HeLa cells have been studied and their cellular localisation properties have been investigated by fluorescence microscopy.

Synthesis and photophysical study of an octahedral silver(I) 1-D coordination polymer with thiocarboxylic-acid-based ligands

We describe the synthesis of a unique 1-D silver coordination polymer, in which the silver metal center is, unusually, six-coordinated. The reaction of 2,3,5,6-tetrakis-(carboxymethylthio)-benzenediol (H2L) and AgNO3 in a 1:2 ratio resulted in the esterification of the carboxylic acid groups and the oxidation of quinol to quinone. As a result, a methylesterthioquinone ligand (L1) was obtained. By increasing the molar ratio of Ag to four equivalents, a 1-D coordination polymer, [AgL1(NO3)]n (1), was obtained. The simple reaction of L1 and AgNO3 in a 1:2 ratio also produced complex 1 in quantitative yield. Both the esterified ligand L1 and the coordination polymer 1 were fully characterized by infrared and 1H NMR spectroscopy, elemental analysis, electrospray ionization mass spectrometry, and single crystal X-ray crystallography. The single crystal X-ray diffraction measurements revealed that the Ag metal center has an octahedral geometry with η2-nitrate ligands. The photophysical properties of complexes are also explored.

Evaluating the Nature of So-Called S*-State Feature in Transient Absorption of Carotenoids in Light-Harvesting Complex 2 (LH2) from Purple Photosynthetic Bacteria.

Carotenoids are a class of natural pigments present in all phototrophic organisms, mainly in their light-harvesting proteins in which they play roles of accessory light absorbers and photoprotectors. Extensive time-resolved spectroscopic studies of these pigments have revealed unexpectedly complex photophysical properties, particularly for carotenoids in light-harvesting LH2 complexes from purple bacteria. An ambiguous, optically forbidden electronic excited state designated as S* has been postulated to be involved in carotenoid excitation relaxation and in an alternative carotenoid-to-bacteriochlorophyll energy transfer pathway, as well as being a precursor of the carotenoid triplet state. However, no definitive and satisfactory origin of the carotenoid S* state in these complexes has been established, despite a wide-ranging series of studies. Here, we resolve the ambiguous origin of the carotenoid S* state in LH2 complex from Rba. sphaeroides by showing that the S* feature can be seen as a combination of ground state absorption bleaching of the carotenoid pool converted to cations and the Stark spectrum of neighbor neutral carotenoids, induced by temporal electric field brought by the carotenoid cation–bacteriochlorophyll anion pair. These findings remove the need to assign an S* state, and thereby significantly simplify the photochemistry of carotenoids in these photosynthetic antenna complexes.

Photophysical, electrochemical, and quantum chemical properties of cationic iridium complexes with tunable emission color

We report the synthesis and characterization of the cationic iridium complexes [Ir(ppy)2(mpoxd)]PF6 (1), [Ir(dfppy)2(mpoxd)]PF6 (2), [Ir(piq)2(mpoxd)]PF6 (3), and [Ir(pq)2(mpoxd)]PF6 (4) bearing 2-phenylpyridine (Hppy), 2-(2,4-difluorophenyl)pyridine (Hdfppy), 1-phenylisoquinoline (Hpiq), and 2-phenylquinoline (Hpq) as cyclometalating ligands and 5-methyl-3-(2-pyridyl)-1,2,4-oxadiazole (mpoxd) as an ancillary ligand. UV–visible absorption spectra, photoluminescence (PL) emission spectra, and cyclic voltammetric measurements were obtained to explore the photophysical and electrochemical properties of 1–4. Depending on the nature of the cyclometalating ligands, the complexes emit yellow-orange to blue light in acetonitrile solution at room temperature. The significant blue shift in the emission spectrum of 2 is due to the presence of electron-withdrawing fluorine atoms on Hdfppy, which stabilizes the highest occupied molecular orbital (HOMO) to a greater extent than in the other complexes. The electrochemical and photophysical properties of the complexes were also calculated using density functional theory (DFT) and time-dependent DFT simulations. The results indicate that the optical properties of the complexes can be effectively tuned by selective design of the cyclometalating and ancillary ligands.

Theoretical investigation on the electronic structures and phosphorescent properties of a series of cyclometalated platinum(II) complexes with different substituted N-heterocyclic carbene ligands

ABSTRACTA series of substituted platinum(II) complexes with a chelating N-heterocyclic carbene (NHC) ligand and a bidentate monoanionic auxiliary ligand (acetylacetone) have been investigated by using the density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, to explore their electronic structures, absorption and emission properties, and phosphorescence quantum efficiency. The influence of different substituted groups on photophysical properties of complexes studied has been detailedly analyzed. The lowest energy absorption and emission wavelengths calculated are comparable to the available experimental values. In addition, ionization potential (IP), electron affinities (EA), and reorganization energy (λ) were obtained to evaluate the charge transfer and balance properties between hole and electron. The calculated results also show that, due to a lower , larger3MLCT contribution, and higher value, the complex 5 owns possibly the largest kr value among these complexes. The theoretical studies could provide useful information for the candidated phosphorescent platinum(II) material for use in the organic light-emitting diodes.

Facile Synthesis of Highly Efficient Lepidine‐Based Phosphorescent Iridium(III) Complexes for Yellow and White Organic Light‐Emitting Diodes

Highly efficient lepidine‐based phosphorescent iridium(III) complexes with pentane‐2,4‐dione or triazolpyridine as ancillary ligands have been designed and prepared by a newly developed facile synthetic route. Fluorine atoms and trifluoromethyl groups have been introduced into the different positions of ligand, and their influence on the photophysical properties of complexes has been investigated in detail. All the triazolpyridine‐based complexes display the blueshifted dual‐peak emission compared to the pentane‐2,4‐dione‐based ones with a broad single‐peak emission. The complexes show emission with broad full width at half maximum (FWHM) over 100 nm, and the emissions are ranges from greenish–yellow to orange region with the absolute quantum efficiency (ΦPL) of 0.21–0.92 in solution, i.e., ΦPL = 0.92 (18), which is the highest value among the reported neutral yellow iridium(III) complexes. Furthermore, high‐performance yellow and complementary‐color‐based white organic light‐emitting diodes (OLEDs) have been fabricated. The FWHMs of the yellow, greenish–yellow OLEDs are in the range of 94–102 nm, which are among the highest values of the reported yellow or greenish–yellow‐emitting devices without excimer emission. The maximum external quantum efficiency of monochrome OLEDs can reach 24.1%, which is also the highest value among the reported yellow or greenish–yellow devices. The color rendering indexes of blue and complementary yellow‐based white OLED is as high as 78.

Flavonols as Luminescent Probes of Water Activity in Foods and Pharmaceuticals

Flavonols are naturally occurring antioxidants with complex photophysical properties. Their emission sensitivity to polarity and hydrogen bonding ability of the local environment suggests their potential as luminescent probes for water activity. Water activity, aw, is an important parameter for ensuring food safety and quality, as it is a determining factor for microbial growth and biochemical reactions.This study focused on 3-hydroxyflavone (3HF), a synthetic molecule that constitutes the backbone of naturally occuring flavonols. However, the photophysical properties and sensitivity to aw of other flavonoid glycosides were also explored. All flavonols were tested in binary solvent mixtures of different aw.3HF is an excited-state intramolecular proton-transfer probe that exhibits dual fluorescent emission bands corresponding to its normal (λem = 405nm) and photo-induced tautomeric (λem = 525nm) form. The normalized intensity of the photo-induced tautomer was sensitive to aw of binary mixtures, with a marked decrease in intensity at aw > 0.8, likely due to progressive aggregation of 3HF molecules. Additional sensitivity to aw was observed in terms of the location of the emission bands. The difference in wavelength between the normal (N) and tautomer (T) forms decreased monotonically at aw > 0.4 due to a hypsochromic shift of the tautomer band. The relative position of the T∗ towards N∗ band as a function of aw was modelled using a log-logistic function. A critical aw value above which the sensitivity of 3HF significantly increased was estimated based on the model.Quercetin and additional flavonoid glycosides were also responsive to changes in aw; e.g., quercetin's fluorescence intensity decreased at aw > 0.6.Although additional validation of these probes in model food systems is required, the available data support the potential use of flavonols as probes of aw in foods and edible pharmceuticals.

Cyclometalated Iridium(III) Bipyridyl–Phenylenediamine Complexes with Multicolor Phosphorescence: Synthesis, Electrochemistry, Photophysics, and Intracellular Nitric Oxide Sensing

We present a new class of phosphorescent cyclometalated iridium(III) bipyridyl-phenylenediamine complexes [Ir(N^C)2 (bpy-DA)](PF6 ) (bpy-DA=4-(N-(2-amino-5-methoxyphenyl)aminomethyl)-4'-methyl-2,2'-bipyridine; HN^C=2-(2,4-difluorophenyl)pyridine (Hdfppy) (1 a), 2-phenylpyridine (Hppy) (2 a), 2-phenylquinoline (Hpq) (3 a), 2-phenylcinchoninic acid methyl ester (Hpqe) (4 a)) and their triazole counterparts [Ir(N^C)2 (bpy-T)](PF6 ) (bpy-T=4-((6-methoxybenzotriazol-1-yl)methyl)-4'-methyl-2,2'-bipyridine; HN^C=Hdfppy (1 b), Hppy (2 b), Hpq (3 b), Hpqe (4 b)). Upon photoexcitation, the diamine complexes exhibited fairly weak green to red phosphorescence under ambient conditions whereas the triazole derivatives emitted strongly. The photophysical properties of complexes 2 a and 2 b have been studied in more detail. Upon protonation, the diamine complex 2 a displayed increased emission intensity, but the emission properties of its triazole counterpart complex 2 b were independent on the pH value of the solution. Also, complex 2 a was found to be readily converted into complex 2 b upon reaction with NO under aerated conditions, resulting in substantial emission enhancement of the solution. The reaction was highly specific toward NO over other reactive oxygen and nitrogen species (RONS) as revealed by spectroscopic analyses. The lipophilicity and cellular uptake efficiency of the diamine complexes have been examined and correlated to their molecular structures. Also, cell-based assays showed that these complexes were noncytotoxic toward human cervix epithelioid carcinoma (HeLa) cells (at 10 μM, 4 h, percentage survival ≈80-95%). Additionally, the diamine complexes have been used to visualize intracellular NO generated both exogenously in HeLa cells and endogenously in RAW 264.7 murine macrophages by laser-scanning confocal microscopy.