Lowest Absorption Band Research Articles

Luminescence of photochromic centers in calcium fluoride crystals doped with Lu3+ ions

We report data on the luminescence spectra associated with photochromic centers in X-ray irradiated calcium fluoride crystals doped with Lu ions. Irradiation in low energy photochromic centers absorption band excites emission, which can be identify with transitions into photochromic centers. Ab initio calculation of absorption spectrum of photochromic center agrees rather well with experimental data.

Synthesis and properties of new mononuclear Ru(II)-based photocatalysts containing 4,4'-diphenyl-2,2'-bipyridyl ligands.

The synthesis and characterisation of a series of eleven new 4,4'-diphenyl-2,2'-bipyridyl derivatives (N^N) with varying 4- or 3,5-substituents on the phenyl rings are reported. The molecular structures of two of these compounds, 4,4'-bis(3,5-diheptyloxyphenyl)-2,2'-bipyridyl and 4,4'-bis(3,5-di-4,4,5,5,5-pentafluoropentyloxyphenyl)-2,2'-bipyridyl are confirmed by X-ray crystallography. Fourteen neutral complexes trans-Ru(II)Cl2(N^N)(CO)2 are prepared by reacting the new proligands and three known ones with the polymeric precursor [Ru(II)Cl2(CO)2]n, and their optical and electrochemical properties are studied. Density functional theory (DFT) and time-dependent DFT calculations have been carried out on selected complexes in order to rationalise their electronic structures and absorption properties. The low energy electronic absorption bands have metal-to-ligand charge-transfer and ligand-to-ligand charge-transfer (LLCT) character, but these dominate only in the 4-substituted species. In the 3,5-disubstituted ones, intraligand charge-transfer (ILCT) within the bpy ligands becomes more important. The complexes show only irreversible reductive electrochemistry and no signs of polymerisation. The photocatalytic oxidation behaviour of selected trans-Ru(II)Cl2(N^N)(CO)2 complexes and their mono-aquo derivatives [Ru(II)(H2O)(CO)2Cl(N^N)](+) with 4-methoxybenzyl alcohol is studied. Turnover numbers of up to ca. 130 are achieved when using [Ru(II)(bpy)3](2+) (bpy = 2,2'-bipyridyl) as photosensitizer and [Co(III)(NH3)5Cl](2+) as a sacrificial oxidant.

Ultra-wideband microwave absorber by connecting multiple absorption bands of two different-sized hyperbolic metamaterial waveguide arrays.

Microwave absorbers have important applications in various areas including stealth, camouflage, and antenna. Here, we have designed an ultra-broadband light absorber by integrating two different-sized tapered hyperbolic metamaterial (HMM) waveguides, each of which has wide but different absorption bands due to broadband slow-light response, into a unit cell. Both the numerical and experimental results demonstrate that in such a design strategy, the low absorption bands between high absorption bands with a single-sized tapered HMM waveguide array can be effectively eliminated, resulting in a largely expanded absorption bandwidth ranging from 2.3 to 40 GHz. The presented ultra-broadband light absorber is also insensitive to polarization and robust against incident angle. Our results offer a further step in developing practical artificial electromagnetic absorbers, which will impact a broad range of applications at microwave frequencies.

Enhancement of the intrinsic fluorescence of adenine using aluminum nanoparticle arrays.

This study demonstrates the metal-enhanced fluorescence of adenine using aluminum nanoparticle arrays in the deep UV range. It achieves the reproducible intensity enhancement of intrinsic fluorescence up to 80 on well-defined aluminum nanoparticle arrays at 257 nm excitation. In addition to a high signal enhancement, a strong modification of the fluorescence emission spectrum of adenine is observed. This study illustrates that the label-free detection of DNA bases and proteins that have low intrinsic fluorescence and absorption bands in the deep UV range can be facilitated using aluminum nanostructures.

Effect of temperature on structural, morphological and magnetic properties of Cd0.7Co0.3Fe2O4 nanoparticles

Cadmium-substituted cobalt ferrite (Cd0.7Co0.3Fe2O4) nanoparticles were synthesized using a chemical synthesis method and synthesized particles were calcinated at 300°C and 600°C respectively. The samples were characterized in order to understand the temperature effect on structural, morphological, thermal, and magnetic properties. X-ray diffraction data confirm the formation of single-phase cubic structure and the average grain sizes were evaluated. The microstructural features were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and compositional analysis carried out by energy dispersive spectroscopy (EDS). A vibrating sample magnetometer (VSM) was used to investigate the magnetic properties. The hysteresis curves of Cd0.7Co0.3Fe2O4 nanoparticles show enhancement of the coercivity with the increasing calcinated temperature. This enhancement is attributed to the transition from a multi-domain to a single-domain nature. The high and low frequency absorption bands of Cd0.7Co0.3Fe2O4 were investigated using FT-IR analysis.

Coupled oscillators for tuning fluorescence properties of squaraine dyes.

Combining a squaraine (S) and a BODIPY (B) chromophore in a heterodimer (SB) and two heterotrimers (BSB and SBS) by alkyne bridges leads to the formation of coupled oscillators whose fluorescence properties are superior compared to the parent squaraine chromophore. The lowest energy absorption and emission properties of these superchromophores are mainly governed by the squaraine part and are shifted by more than 1000 cm(-1) to the red by excitonic interaction between the squaraine and the BODIPY dye. Employing polarization-dependent transient absorption and fluorescence upconversion measurements, we could prove that the lowest energy absorption in SB and BSB is caused by a single excitonic state but by two for SBS. Despite the spectral red-shift of their lowest absorption band, the fluorescence quantum yields increase for SB and BSB compared to the parent squaraine chromophore SQA. This is caused by intensity borrowing from the BODIPY states, which increases the squared transition moments of the lowest energy band dramatically by 29% for SB and 63% for BSB compared to SQA. Thereby, exciton coupling leads to a substantial enhancement of fluorescence quantum yield by 26% for SB and by 46% for BSB and shifts the emission from the red into the near-infrared. In this way, the BODIPY-squaraine conjugates combine the best properties of each class of dye. Thus, exciton coupling in heterodimers and -trimers is a valuable alternative to tuning fluorescence properties by, e.g., attaching substituents to chromophores.

Wide Band Gap Transparent Polymer-Inorganic Composite Thin Films by Dip-Coating Method: Preparation and Characterizations

Wide band gap transparent polymer-inorganic (PVA-ZnO) composite thin films were prepared by the dip-coating method. Functional groups and metal oxide vibrations were found from Fourier transform-infrared spectroscopy. The elements Zn and O were confirmed from energy dispersive X-ray spectroscopy. The X-ray diffraction patterns revealed that the sharp diffraction peaks correspond to the hexagonal wurtzite structure of ZnO in the PVA matrix. Scanning electron microscopy images showed that the ZnO nanoparticles are randomly distributed throughout the entire film surface. The optical study reveals that the transmittance was more than 85% with very low absorption and wide band gap energy (4.03 to 3.95 eV). The obtained results indicate that the high transmittance, very low absorption, and wide band gap energy of the prepared dip-coated composite thin films make them suitable for use in transparent optoelectronic device applications in the near future.

Photodissociation dynamics of C₃H₅I in the near-ultraviolet region.

The ultraviolet photodissociation dynamics of allyl iodide (C3H5I) have been studied by ion-imaging at 266 nm and 213 nm. These photolysis wavelengths are located in the two lowest absorption bands in the near-ultraviolet region. The atomic iodine products were detected by [2+1] resonantly enhanced multiphoton ionization spectroscopy. The spectra showed that the branching fraction for the spin-orbit excited ((2)P(1/2)) state was larger than that for the ground ((2)P(3/2)) state at both photolysis wavelengths. The state-resolved scattering images of iodine showed two maxima in the velocity distributions in the (2)P(3/2) state and a single peak in the (2)P(1/2) state. The spin-orbit specificity indicates that the C-I bond cleavage at both absorption bands is governed by the dissociative n(I)σ*(C-I) potential energy surfaces. The nascent internal energy distribution of the allyl radical (C3H5) counter product, which was obtained by the analysis of the state-resolved scattering distributions, showed a marked difference between the photolysis at 266 nm and 213 nm. The generation of the colder C3H5 with the higher translational energy at 266 nm implied the direct photoexcitation to the n(I)σ*(C-I) repulsive surfaces, whereas the internally hot C3H5 at 213 nm was ascribed to the local π(CC)π*(CC) photoinitiation in the allyl framework followed by predissociation to the n(I)σ*(C-I) states.

Half-Lantern Pt(II) and Pt(III) Complexes. New Cyclometalated Platinum Derivatives

The divalent complex [{Pt(bzq)(μ-L)}2] (1) [Hbzq = benzo[h]quinolone, HL = CF3C4H2N2SH: 4-(trifluoromethyl)pyrimidine-2-thiol] was obtained from equimolar amounts of [Pt(bzq)(NCMe)2]ClO4 and 4-(trifluoromethyl)pyrimidine-2-thiol with an excess of NEt3. The presence of a low intensity absorption band at 486 nm (CH2Cl2), assignable to a metal-metal-to-ligand charge transfer transition (1MMLCT) [dσ*(Pt)2→π*(bzq)], is indicative of the existence of two platinum centers located in close proximity because the rigidity of the half-lantern structure allows the preservation of these interactions in solution. Compound 1 undergoes two-electron oxidation upon treatment with halogens X2 (X2: Cl2, Br2 or I2) to give the corresponding dihalodiplatinum (III) complexes [{Pt(bzq)(μ-L)X}2] (L = CF3C4H2N2S-κN,S; X: Cl 2, Br 3, I 4). Complexes 2–4 were also obtained by reaction of 1 with HX (molar ratio 1:2, 10% excess of HX) in THF with yields of about 80% and compound 2 was also obtained by reaction of [{Pt(bzq)(μ-Cl)}2] with HL (4-(trifluoromethyl)pyrimidine-2-thiol) in molar ratio 1:2 in THF, although in small yield. The X-ray structures of 2 and 3 confirmed the half-lantern structure and the anti configuration of the molecules. Both of them show Pt–Pt distances (2.61188(15) Å 2, 2.61767(16) Å 3) in the low range of those observed in Pt2(III,III)X2 half-lantern complexes.

Elastic properties of germanium substituted lithium ferrite

Polycrystalline ferrites with general formula Li0.5+0.5xGexFe2.5−1.5xO4 (where x=0.0, 0.1, 0.2, 0.3 and 0.4) were prepared by the standard ceramic technique. The analysis of XRD patterns revealed the formation of single-phase cubic spinel structure. The lattice constant was found to decrease with the increase in germanium content. Infrared spectra were performed at room temperature in the wave number range of 200–1000cm−1. Two prominent bands were observed; high frequency band ‘υ1’ around 583cm−1 is assigned to the tetrahedral complexes and low frequency band ‘υ2’ around 392cm−1 is assigned to the octahedral complexes. Low frequency absorption band ‘υ3’ appeared at 240cm−1 is assigned to lattice vibrations. Force constant for the tetrahedral and octahedral sites was calculated by using IR data. Elastic moduli such as Young’s modulus (E), bulk modulus (B), modulus of rigidity (G), Poisson ratio (σ) and Debye temperature (θD) were determined. In the present work the elastic moduli increase with germanium content whereas Poisson’s ratio almost remains constant. A linear relationship between Debye temperature and average sound velocity was observed.

Role of surface states and defects in the ultrafast nonlinear optical properties of CuS quantum dots

We report facile preparation of water dispersible CuS quantum dots (2–4 nm) and nanoparticles (5–11 nm) through a nontoxic, green, one-pot synthesis method. Optical and microstructural studies indicate the presence of surface states and defects (dislocations, stacking faults, and twins) in the quantum dots. The smaller crystallite size and quantum dot formation have significant effects on the high energy excitonic and low energy plasmonic absorption bands. Effective two-photon absorption coefficients measured using 100 fs laser pulses employing open-aperture Z-scan in the plasmonic region of 800 nm reveal that CuS quantum dots are better ultrafast optical limiters compared to CuS nanoparticles.

Copper substitution effect on the structural properties of nickel ferrites

Nickel–copper ferrites with the general formula Ni1−x Cux Fe2 O4 (0≤x≤1) were studied using X-ray diffraction and infrared absorption spectroscopy. XRD diffraction patterns show that all samples have a pure single-phase cubic spinel structure over the whole composition range. From these patterns, the lattice parameters, crystallite size and porosity of these samples have been calculated and compared with those predicted theoretically. Most of the values were found to increase with increasing Cu content. Far infrared absorption spectra show high and low absorption bands corresponding to tetrahedral and octahedral sites confirming the single phase spinnel structure. The calculated force constants, Kt and Ko for the two sites are found to increase with increasing Cu content and their relative values are consistent with bond length magnitudes at tetrahedral and octahedral sites.

Structural and magnetic studies on Zr doped ZnO diluted magnetic semiconductor

In this study, Zirconium doped Zn1−xZrxO (with x = 0.00–0.10) samples have been prepared by formal solid-state reaction technique. The Zr doped ZnO samples annealed at 1100 °C and characterized by different characterization techniques, such as X-ray diffraction (XRD), Scanning electron microscope (SEM), Vibrating sample magnetometer (VSM) and Fourier transform infrared spectroscopy (FTIR). The X-ray diffraction (XRD) used to study the structural properties. XRD pattern showed that lattice parameters, “a”, “c”, unit cell volume and Zn–O bond length increase with doping content (x ≤ 0.04) where as these decrease with x > 0.04. On the other hand, reverse trend observed with lattice distortion. The crystallite size decreases with increasing doping content of Zr. FTIR employed to investigate functional chemical bonding properties of different elements and compounds present in materials. The low, medium and high frequency absorption bands observed at 630, 1500 and 3435 cm−1, which were the common features of Zn–O, H–O–H and O–H bond respectively. SEM used to study surface morphology and measured grain size of specimen. The surface becomes dense and grain size decreases with increasing degree of Zr contents. The SEM micrograph also shows the presence of spherical micro size particles and formation of pores in samples. Magnetic properties were obtained using VSM. The samples exhibit room temperature ferromagnetism. The magnetic hysteresis loops show variation in the value of magnetic parameter. The saturation magnetization (Ms) and coercivity (Hc) decrease, while remanence magnetization (Mr) shows gradually increasing trend with Zr content. VSM measurement reveals that sample Zn0.96Zr0.4O show better result as compared to x = 0.06–0.10.

Potential energy surfaces for ground and excited electronic states of the CF3I molecule and their relevance to its A-band photodissociation

The multireference spin-orbit (SO) configuration interaction (CI) method in its Λ-S contracted SO-CI version is employed to calculate two-dimensional potential energy surfaces for the ground and low-lying excited states of CF3I relevant to its photodissociation in the lowest absorption band (A band). The computed equilibrium geometry for the X̃A1 ground state and vibrational frequency ν3 for the C-I stretch mode agree well with available experimental data. The (3)Q0(+) state dissociating to the excited I((2)P1/2) limit is found to have a minimum of 1570 cm(-1) significantly shifted to larger internuclear distances (RC-I = 5.3 a0) relative to the ground state. Similar to the CH3I case, this makes a single-exponent approximation commonly employed for analysis of the CF3I recoil dynamics unsuitable. The 4E((3)A1) state possessing an allowed transition from the ground state and converging to the same atomic limit as (3)Q0(+) is calculated to lie too high in the Franck-Condon region to have any significant impact on the A-band absorption. The computed vertical excitation energies for the (3)Q1, (3)Q0(+), and (1)Q states indicate that the A-band spectrum must lie approximately between 31,300 and 45,200 cm(-1), i.e., between 220 and 320 nm. This result is in very good agreement with the measured absorption spectrum.

Stabilization of oxidovanadium(iv) by organic radicals

o-Imino-p-R'-benzosemiquinone anion radical (L(R')(IS)(˙-)) complexes of oxidovanadium(IV) of type [(L(1)(R-))(VO(2+))(L(R')(IS)(˙-))] (R = H, R' = H, 1; R = H, R' = -CMe(3), 2; R = -CMe(3), R' = H, 3 and R = -CMe(3), R' = -CMe(3), 4) incorporating the redox-innocent tridentate NNO-donor L(1)(R-) ligands (L(1)(R)H = 2,4-di-R-6-{(2-(pyridin-2-yl)hydrazono)methyl}phenol) were isolated and substantiated by elemental analyses, IR, mass, NMR and UV-vis spectra including the single crystal X-ray structure determinations. The V-O(phenolato) (cis to the V=O) lengths spanning 1.905(3)-1.9355(15) Å in 1-4 are consistent with the coordination to the [VO](2+) state. The V-O(IS) (trans to the V=O) lengths, 2.1505(17)-2.1869(15) Å, in 1-4 are longer due to the trans influence of the V=O bond. The V-N(IS) lengths, 1.906(3)-1.924(2) Å, in 1-4 are comparatively shorter due to the higher affinity of the paramagnetic [VO](2+) ion towards the L(R')(IS)(˙-) anion radicals. Density functional theory (DFT) calculations using B3LYP, B3PW91 and PBE1PBE functionals on 1 and 2 authenticated that the closed shell singlet (CSS) solutions (dianionic o-amido-p-R'-phenolates (L(R')(AP)(2-)) coordinated to VO(3+), Type I) of 1-4 are unstable with respect to the open shell singlet (OSS) perturbations. Broken symmetry, BS (1,1) M(s) = 0 (L(R')(IS)(˙-) coordinated to the VO(2+) ion, Type III) solutions of 1-4 are stable and reproduce the experimental bond parameters. Frozen glasses EPR spectra of [1-4](+) ions (e.g. g(||) = 1.948, g(⊥) = 1.978, A(||) = 184 (22 G), A(⊥) = 62(15 G) for [2](+)) and unrestricted DFT calculations on [1](+), [2](+), [1](-) and [2](-) ions using doublet spin state elucidated that the reversible anodic waves at [0.15-0.31] V of 1-4 complexes are due to the oxidation of L(R')(IS)(˙-) generating [(L(1)(R-))(VO(2+))(L(R')(IQ))]+ complexes (L(R')(IQ) = o-imino-p-R'-benzoquinone) coordinated to the [VO](2+) ion (Type V) while the irreversible cathodic waves at -[1.08-1.49] V are due to the formation of unstable [(L(1)(R-))(VO(2+))(L(R')(AP)(2-))](-) complexes (Type II). The second anodic waves at [0.76-0.89] V are assigned to a [VO](3+)-[VO](2+) couple affording diamagnetic [(L(1)(R-))(VO(3+))(L(R')(IQ))](2+), [1-4](2+) complexes (Type VI) which are identified by UV-vis spectra, DFT and time dependent (TD) DFT calculations. Spectro-electrochemical measurements and TD DFT calculations on 1 and 2 disclosed that lower energy electronic absorption bands of 1-4 are due to the LMCT and CSS-OSS perturbation which disappear in [1-4](+) ions. [1-4](+) absorb at 600-650 nm due to d-d transitions and MLCT which are absent in VO(3+) complexes, [1-4](2+).

ANOMALY DETECTION AND COMPARATIVE ANALYSIS OF HYDROTHERMAL ALTERATION MATERIALS TROUGH HYPERSPECTRAL MULTISENSOR DATA IN THE TURRIALBA VOLCANO

Abstract. The aim of this work is the comparative study of the presence of hydrothermal alteration materials in the Turrialba volcano (Costa Rica) in relation with computed spectral anomalies from multitemporal and multisensor data adquired in spectral ranges of the visible (VIS), short wave infrared (SWIR) and thermal infrared (TIR). We used for this purposes hyperspectral and multispectral images from the HyMAP and MASTER airborne sensors, and ASTER and Hyperion scenes in a period between 2002 and 2010. Field radiometry was applied in order to remove the atmospheric contribution in an empirical line method. HyMAP and MASTER images were georeferenced directly thanks to positioning and orientation data that were measured at the same time in the acquisition campaign from an inertial system based on GPS/IMU. These two important steps were allowed the identification of spectral diagnostic bands of hydrothermal alteration minerals and the accuracy spatial correlation. Enviromental impact of the volcano activity has been studied through different vegetation indexes and soil patterns. Have been mapped hydrothermal materials in the crater of the volcano, in fact currently active, and their surrounding carrying out a principal components analysis differentiated for a high and low absorption bands to characterize accumulations of kaolinite, illite, alunite and kaolinite+smectite, delimitating zones with the presence of these minerals. Spectral anomalies have been calculated on a comparative study of methods pixel and subpixel focused in thermal bands fused with high-resolution images. Results are presented as an approach based on expert whose main interest lies in the automated identification of patterns of hydrothermal altered materials without prior knowledge or poor information on the area.

Optical Properties of Oligothiophene Substituted Diketopyrrolopyrrole Derivatives in the Solid Phase: Joint J- and H-Type Aggregation

Photophysical properties of diketopyrrolopyrrole derivatives substituted with oligothiophenes are investigated. All compounds are found to be fluorescent both in solution and in the solid phase. At low temperature in the solid, fluorescence originates from excimer-like excited states. Comparison of absorption and fluorescence excitation spectra taken under matrix isolated conditions and on solid films show the presence of both J- and H-type absorption bands in the solid phase. Quantum-chemical calculations, including exciton-phonon coupling to account for deviations from the Born-Oppenheimer approximation, are performed to simulate the band shape of the lowest absorption band in the molecular solid. The joint presence of J- and H-bands is explained by the presence of two molecules in the unit cell. The Davydov splitting is substantial for molecules with linear alkyl substituents on the nitrogen atom (on the order of 0.2 eV) but can be reduced to almost zero by introducing branching at the β-carbon of the alkyl side chain.

Transmittance and optical constants of Sr films in the 6–1220 eV spectral range

Strontium (Sr) is a material with low-absorption bands in the extreme ultraviolet (EUV), which makes it a potential candidate for band pass filters and multilayer coatings. Yet, a better knowledge of the optical properties of Sr is required for these developments. The optical constants n and k of Sr thin films have been obtained in the 6–1220 eV range from transmittance measurements performed at room temperature. These are the first experimental optical constant data of Sr in most of the range. Thin films of Sr with various thicknesses were deposited by evaporation in ultrahigh vacuum conditions, and their transmittance was measured in situ. Sr films were deposited onto grids coated with a thin C support film. Transmittance measurements were used to directly obtain the extinction coefficient k of Sr films. The refractive index n of Sr was calculated with Kramers-Krönig analysis. For this, k data were extrapolated both on the high- and on the low-energy sides by using experimental and calculated k data available in the literature. It was found that, similar to other alkaline-earth metals, Sr has a low absorption band in the EUV, which for Sr is below its N2,3 edge, with a minimum at ∼18.5 eV, a range where most materials in nature have a large absorption. A second spectral range of interest for the low absorption of Sr is below its M4,5 edge at 132 eV. In spite of these remarkable properties, Sr is a very reactive material and the stability of coatings encompassing Sr may be an issue. Good consistency of the data resulted from the application of f and inertial sum rules.

Microwave assisted combustion synthesis of CdFe2O4: Magnetic and electrical properties

CdFe2O4 particles were synthesized by the microwave assisted combustion method using two different fuels—glycine and urea. Microwave heating provides higher chemical yield within a minute. The synthesized particles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), ac impedance spectroscopy, vibrating sample magnetometry (VSM) and electron spin resonance (ESR) methods. XRD analysis shows the cubic structure of CdFe2O4. The high and low frequency absorption bands of CdFe2O4 were found using FTIR analysis. Spherical morphology was revealed from the SEM images. ESR and VSM measurements reveal the antiferromagnetic behavior of CdFe2O4. The electrical conductivities of CdFe2O4 synthesized using glycine and urea are 6.5×10−7Scm−1 and 4.7×10−8Scm−1 respectively at 240oC. At elevated temperatures an occurrence of increase in conductivity was observed, which indicates the semiconducting behavior of CdFe2O4. The dielectric spectral analysis reveals that dielectric constant of CdFe2O4 decreases with frequency and increases with temperature.

Electronic structures and spectral properties of rhenium(I) tricarbonyl diimine complexes with phosphine ligands: DFT/TDDFT theoretical investigations

The ground and excited state geometries and frontier molecular orbital, absorption and emission properties of the four transition metal complexes Re(bpy)(CO)3(PEt3)+ (1), Re(bpy)(CO)3(PPh3)+ (2), Re(bpy)(CO)3[P(OEt3)]+ (3) and Re(bpy)(CO)3[P(OPh3)]+ (4) were studied theoretically. The introduction of different phosphine ligands significantly changed the geometric parameters of the complexes. The axial Re–C bond distance was longer than the equatorial Re–C bond distance. The lowest lying absorption bands of 1 and 2 have HOMO→LUMO transition configurations resulting in MLCT/LLCT transition characteristics. The HOMO-1→LUMO transition predominantly contributed to the lowest absorption bands of 3 with MLCT/LLCT characteristics. The absorption band of 4 at 326nm was dominated by HOMO-4→LUMO and HOMO-6→LUMO transitions with mixed MLCT/LLCT characteristics. The phosphorescence emission energies of 1–4 were also calculated and compared with the experimental values.