Long-wavelength Band Research Articles

Synthesis and molecular characterization of 5,5′-((2,4-dichlorophenyl)methylene)bis(1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione)

A simple, economical, and green approach to the synthesis of 5,5′-((2,4-dichlorophenyl)methylene)bis(1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione) 4 using a tandem Aldol condensation-Michael addition process in aqueous diethylamine medium was described. The 3D structure of the latter was confirmed by single-crystal X-ray structure determination. The molecular structure of the titled compound was calculated using DFT B3LYP/6-311G(d,p) method. The calculated geometric parameters are in good agreement with the experimental data obtained from our reported X-ay structure. The two pyrimidinetrione rings have C16 and C20 atoms deviated significantly from the ring plane. The electronic spectra of the studied compound have been calculated using the TD-DFT method. The longest wavelength band (257.8nm, f=0.0276) occurs due to H→L (86%) transition. The 1H and 13C NMR calculated chemical shifts using GIAO method showed good correlation with the experimental data. The molecular electrostatic potential (MEP) showed that the most reactive sites for electrophilic and nucleophilic attacks are the carbonyl oxygen (O5) and the H21 atoms, respectively. The NBO calculations were performed to predict the natural atomic charges at the different atomic sites and to study the different intramolecular charge transfer (ICT) interactions occurring in the studied system. Interestingly, there is some delocalization of electron densities from the occupied σ-type NBO of the C20H21 to the unoccupied π∗-NBO of the two adjacent carbonyl groups.

Synthesis and properties of azonaphtharylamide pigments having arylamide groups at 2- and 7-positions

We studied two azonaphtharylamide pigments having arylamide groups at the 2- and 7-positions on the naphthol ring. Presence of the 7-substited amide group distinguishes the pigments from conventional azonaphtharylamide pigments derived from 3-hydroxy-2-naphthoic acid. The 7-substituent caused a hyperchromic effect but did not produce bathochromic shift in the optical absorption spectra in solution compared with the corresponding 7-unsubstituted counterparts. Molecular geometry optimizations through semi-empirical MO calculations showed that extent of the chromophore systems in the pigments with and without the 7-substituent is nearly the same, which is consistent with absence of the bathochromic shift. The MO calculations also showed that the MOs localized in the 7-substituents are involved in the electronic transitions in the longest wavelength bands of the pigments, which is responsible for the hyperchromic effect. The 7-substituted pigments exhibited better resistivity to light and heat than the 7-unsubstituted ones.

Synthesis, spectral, and electrochemical studies of electronically tunable β-substituted porphyrins with mixed substituent pattern.

Two new families of porphyrins with mixed substituent pattern, viz. 2-nitro-12,13-disubstituted-meso-tetraphenylporphyrins (H2TPP(NO2)X2, X = Ph, phenylethynyl (PE), 2-thienyl (Th), Br, and CN) and 2-nitro-7,8,12,13,17,18-hexasubstituted-meso-tetraphenylporphyrins (H2TPP(NO2)X6, X = Br, Ph, PE, and Th), and their metal (Co(II), Ni(II), Cu(II), and Zn(II)) complexes have been synthesized and characterized. H2TPP(NO2)X6 exhibited remarkable red shift in the Soret band (45-70 nm) and longest wavelength band, Qx(0,0) (65-90 nm), as compared to H2TPP(NO2). Single-crystal structures of MTPP(NO2)X2 (M = Zn(II) and Ni(II); X = Br, Ph, and PE) showed quasi-planar conformation, whereas H2TPP(NO2)Th2 and NiTPP(NO2)Br6 exhibited moderate and highly nonplanar saddle-shape conformations, respectively. Further, DFT fully optimized geometries of H2TPP(NO2)X2 and H2TPP(NO2)X6 revealed moderate and severe saddle-shape nonplanar conformations, respectively. The imino proton resonances of H2TPP(NO2)X6 are significantly downfield shifted (Δδ = 1.10-1.80 ppm) relative to H2TPP(NO2). Mixed substituted highly nonplanar porphyrins exhibited higher protonation and deprotonation constants relative to H2TPPX8 (X = Cl and Br). The redox tunability was achieved by introducing electron donor (Ph and Th) and acceptor (PE, Br, and CN) groups on the MTPP(NO2) backbone. The unusual variation in the spectral and electrochemical redox properties of mixed substituted porphyrins are interpreted in terms of both an inductive and a resonance interaction of substituents on the porphyrin π-system as well as nonplanarity of the macrocycle.

Edge Luminescence of ZnO Films

The luminescence spectra of some zinc oxide films near the exciton band have a very wide long-wavelength band. Its intensity increases with the excitation level much more rapidly than the intensity of the exciton bands, which even decreases for some films. It is shown experimentally that the long-wavelength band is not the P-line and is most likely caused by an intrinsic defect or random impurity in the ZnO. An interpretation of this effect based on the Burstein–Moss effect is proposed. A system of rate equations that include a number of parameters is set up for approximate modelling of this effect. These parameters can be chosen so that a numerical solution of this system yields a dependence of the intensity ratio of these bands on the excitation level and (in some cases) a drop in the intensity of the exciton band with increasing excitation level that is close to experiment.

Linear and nonlinear optical properties of merocyanines derivatives of malonodinytriles

A detailed complex study of the series of neutral merocyanine derivatives of malonodinytriles with variable donor terminal groups and with the same acceptor group is carried out. The absorption spectra and nonlinear optical (NLO) characteristics are measured. It is shown that the long-wavelength absorption band is highly sensitive to the donor strength of the variable residue terminal group. The distinct dependence of the state dipole moments and characteristics of the electron transitions on the chemical constitution of merocyanine molecules was confirmed by quantum-chemical calculations. An analysis of the obtained results shows that the change in the electron characteristics of the ground and excited states due to variations in the chemical constitution of merocyanine molecules is accompanied by sensible variations in the NLO response. With allowance for the calculation, the effect of molecular topology on the experimental linear and NLO characteristics could be correctly interpreted.

Dynamics of trans-cis photoisomerization of hetarylazo dyes

Dynamics of trans-cis photoisomerization of novel hetarylazo dyes containing hydrogenated quinoline and triazole or tetrazole moieties has been studied by femtosecond laser photolysis with spectrophotometric detection. For all the dyes under study, the absorbance dynamics after photoexcitation in the long-wavelength absorption band (λpump = 550 nm) is described by three fast processes with characteristic times of 0.07–0.27, 0.4–1.0, and 3–7 ps. The effect of the solvent and the azo dye structure on the dynamics of transient species has been investigated.

Synthesis and optoelectronic properties of novel fluorene-bridged dinuclear cyclometalated iridium (III) complex with A–D–A framework in the single-emissive-layer WOLEDs

To explore the influence of push–pull chromophores on properties of emitter in organic light-emitting devices (OLEDs), an acceptor–donor–acceptor (A–D–A)-based dinuclear iridium (III) complex of (dfppy)4Ir2(dipic-FL) was synthesized via Suzuki coupling reaction, in which dfppy is 2-(2,4-difluorophenyl)pyridine and dipic-FL is 2,7-di(5-pyridyl-2-carboxyl)-9,9-dioctyl-9H-fluorene. An intense emission peak at about 480nm resulting from the (dfppy)2Ir(pic) chromophore and a weak long-wavelength emission band at 580–660nm attributed to intramolecular charge transfer transition were exhibited for (dfppy)4Ir2(dipic-FL) in dichloromethane solution. But a remarkably hypsochromic photoluminescence profile with an intense characteristical emission peak at 422nm was observed, which is attributed to the intraligand (IL) π–π∗ excited states in its thin film. White emission with a maximum luminance of 1040cd/m2 and current efficiency of 1.2cd/A was obtained in its single-emissive-layer (SEL) OLEDs with a configuration of ITO/PEDOT:PSS/(dfppy)4Ir2(dipic-FL) (10 wt%):TCTA/TPBi/LiF/Al. To our knowledge, this is one of the best examples in term of dinuclear iridium complex as single dopant in the high-performance white-emitting SEL-OLEDs.

Excited-state dynamics of 3-hydroxyflavone anion in alcohols.

The electronic absorption spectrum of 3-hydroxyflavone (3HF) in various solvents exhibits a long-wavelength (LW) band, whose origin has been debated. The excited-state dynamics of neutral and basic solutions of 3HF in alcohols upon excitation in this LW band has been investigated using a combination of fluorescence up-conversion and transient electronic and vibrational absorption spectroscopies. The ensemble of results reveals that, in neutral solutions, LW excitation results in the population of two excited species with similar fluorescence spectra but very different lifetimes, namely 40-100 ps and 2-3 ns, depending on the solvent. In basic solutions, the relative concentrations of these species change considerably in favor of that with the short-lived excited state. On the basis of the spectroscopic data and quantum chemistry calculations, the short lifetime is attributed to the excited state of 3HF anion, whereas the long one is tentatively assigned to an excited hydrogen-bonded complex with the solvent. Excited-state intermolecular proton transfer from the solvent to the anion yielding the tautomeric form of 3HF is not operative, as the excited anion decays to the ground state via an efficient nonradiative transition.

Effect of structural phase transitions on the exciton absorption spectrum of thin CsPbCl3 films

The absorption spectrum of thin film CsPbCl3 in the 2–6 eV range is studied at temperatures of 90–500 K. Sudden changes show up in the temperature dependences of the parameters of the long-wavelength exciton band (spectral position Em(T), half width Γ(T), and oscillator strength f(T)) at the first order phase transitions at 310 and 320. No phase transitions in Em(T), Γ(T), and f(T) are detected at low temperatures. The exciton excitations in CsPbCl3 are found to have a three-dimensional character.

Flattop Broadband Wavelength Conversion Based on Cascaded Second-Harmonic Generation and Difference Frequency Generation in Step-Segmented Quasi-Phase Matched Gratings

Bandwidth enhancement and response flattening of wavelength conversion based on single-pass and double-pass cascaded second harmonic generation and difference frequency generation in step-segmented quasi-phase matched (QPM) gratings are investigated. For the same waveguide length, high conversion efficiency, flat response and broad signal bandwidth can be obtained simultaneously by optimizing the poling period of the step-segmented QPM structure. The conversion bandwidths in a 3-cm-long five-step-segmented waveguide are 134 nm for single-pass scheme and 132 nm for the double-pass one, respectively, which are both over the whole conventional band and long-wavelength band. The ripple on the matching response can keeps less than 0.2 dB as well.

Spectral Properties of the Anionic Form of the Molecular Probe Fet

The relationship of the fl uorescence spectral characteristics of the anionic form of the molecular probe 4ƍ -(diethylamino)-3-hydroxyfl avone (FET) to intramolecular proton transfer in a weakly polar solvent (CH2Cl2) was studied. The fl uorescence spectrum of this form had a broad featureless band in the area between the shortwavelength and long-wavelength fl uorescence bands of FET. Its excitation spectrum had strong UV maxima (350 and 305 nm). This fl uorescence disappeared completely if the solution was cooled to 1°C. The deprotonation mechanism of neutral FET molecules was discussed.

HPLC coupled with a spectrophotometer as a reliable setup for the study of absorption properties of imidazolium ionic liquids using bmimBF4as an example

The absorption spectra of the same ionic liquid published by many authors show significant differences, which are interpreted as being caused by the presence of many difficult to eliminate impurities. This paper presents an innovative use of an HPLC system coupled with a spectrophotometer, which allows separation of impurities from bmimBF4, and to a high degree, separation of bmimBF4-related species, determination of their relative content and measurement of their absorption spectra. The absorption spectra of bmimBF4 aggregates and water complexes show a long-wavelength absorption band (λmax = 278 nm) but with different molar absorption coefficients, e. The absorption spectrum measured by a spectrophotometer is a sum of the absorption spectra of all species derived from bmimBF4 and the impurities that it contains, while the use of the proposed setup provides reliable results on the spectral properties of different compounds showing complex and/or difficult to study properties even if they contain numerous impurities.

From yellow to pink using a fluorimetric and colorimetric pyrene derivative and mercury (II) ions

A new simple and multifunctional fluorescent probe based on pyrene linked through an imine bond to a hydroxyphenol unit was synthesised, fully characterized and investigated in solution. Additionally, its behaviour in the presence of several ions (H+, Zn2+, Cd2+, Cu2+, Ni2+, Pb2+, Fe2+, Hg2+ and Al3+) was investigated in CH2Cl2. It was found that the absorption spectra of probe 1 shows no differences for all ions titrations except in the presence of H+ and Hg2+ where a new longer wavelength band becomes visible (inducing a colour change from yellow to orange and pink, respectively). In the emission, a blue-shift and an enhancement of the fluorescence of the probe for all metal ions was observed with the exception of Al3+ where no detectable changes could be observed. The probe was found to be selective for Hg2+ ion at low concentrations (till one equivalent).

Soliton-based ultrafast multi-wavelength nonlinear switching in dual-core photonic crystal fibre

Systematic experimental study of ultrafast multi-wavelength all-optical switching performance in a dual-core photonic crystal fibre is presented. The focus is on nonlinearly induced switching between the two output ports at non-excitation wavelengths, which are generated during nonlinear propagation of femtosecond pulses in the anomalous dispersion region of a dual-core photonic crystal fibre made of multicomponent glass. Spatial and spectral characteristics of the fibre output radiation were measured separately for both fibre cores under various polarization and intensity conditions upon selective, individual excitation of each fibre core. Polarization-controlled nonlinear switching performance at multiple non-excitation wavelengths was demonstrated in the long-wavelength optical communication bands and beyond. Depending on the input pulse polarization, narrowband switching operation at 1560 nm and 1730 nm takes place with double core extinction ratio contrasts of 9 dB and 14.5 dB, respectively. Moreover, our approach allows switching with simultaneous wavelength shift from 1650 to 1775 nm with extinction ratio contrast larger than 18 dB. In addition, non-reciprocal behaviour of the soliton fission process under different fibre core excitations was observed and its effect on the multi-wavelength nonlinear switching performance was explained, taking into account the slight dual-core structure asymmetry. The obtained results represent ultrafast all-optical switching with an extended dimension of wavelength shift, controllable with both the input radiation intensity and the polarization by simple propagation along a 14 mm long fibre.

Photophysical, NMR and density functional study on the ion interaction of norharmane: proton transfer vs. hydrogen bonding

Interactions of norharmane (S), with different ions have been studied using spectroscopy, NMR and density functional studies. A significant gradual change both in absorption and emission spectra was observed upon addition of fluoride anions. The spectral change in the absorption and emission bands of norharmane (S) is found to be specific to fluoride ion; it is unaffected by the presence of other ions. Hydrogen bond mediated proton transfer from norharmane to fluoride is mainly attributed to the fluoride selective signaling behavior. Calculations of the transition energies of the norharmane (S), anionic species of norharmane (S−) and hydrogen bonded complexes (S⋯F−) show that the added fluoride anion could capture the proton in the free N–H moiety instead of the hydrogen-bonding one. Experimental results reveal that the long-wavelength absorption band in the presence of fluoride ion is due to the formation of anion.

Engineering absorption and blackbody radiation in the far-infrared with surface phonon polaritons on gallium phosphide

We demonstrate excitation of surface phonon polaritons on patterned gallium phosphide surfaces. Control over the light-polariton coupling frequencies is demonstrated by changing the pattern periodicity and used to experimentally determine the gallium phosphide surface phonon polariton dispersion curve. Selective emission via out-coupling of thermally excited surface phonon polaritons is experimentally demonstrated. Samples are characterized experimentally by Fourier transform infrared reflection and emission spectroscopy, and modeled using finite element techniques and rigorous coupled wave analysis. The use of phonon resonances for control of emissivity and excitation of bound surface waves offers a potential tool for the exploration of long-wavelength Reststrahlen band frequencies.

Extra-broadband wavelength-tunable actively mode-locked short-cavity fiber ring laser using a bismuth-based highly nonlinear erbium-doped fiber

We demonstrate an ultra-wideband wavelength-tunable actively mode-locked short-cavity laser employing a 151-cm-long bismuth-based highly nonlinear erbium-doped fiber (Bi-HNL-EDF). A wavelength tuning range of 87nm from 1533nm to 1620nm can be achieved because the Bi-HNL-EDF has an ultra-wide gain bandwidth. High nonlinearity of the Bi-HNL-EDF also collaborates with spectral filtering by an optical bandpass filter to suppress the supermode noise quite effectively. Total length of the fiber ring cavity is as short as 16m. Thus, stable and clean 5.6–6.1ps pulses with a repetition rate of 10GHz are successfully obtained over the wavelength tuning range almost completely covering both the conventional wavelength band (1530–1565nm) and the longer wavelength band (1565–1625nm). The bismuth-based short-cavity fiber laser also shows good performance in the back-to-back bit-error-rate measurements, and maintains bit-error-free mode-locking operation throughout the entire wavelength tuning range.

A solvatochromic study of N-[4-(9-acridinylamino)-3-methoxyphenyl]methanesulfonamide hydrochloride: An experimental and theoretical approach

The effects of a solvent on the position of the long-wavelength electronic absorption band of N-[4-(9-acridinylamino)-3-methoxyphenyl]methanesulfonamide hydrochloride [m-AMSA.HCl], an antitumor drug, were investigated. To assess the nature of molecular interactions of protonated m-AMSA (1) with various organic solvents the solvatochromic shifts of absorption maxima (ν‾A) with (i) traditionally used bulk solvent polarity functions (Δf and F(ε, n)) and (ii) empirical scales of solvent polarity (Z, χB and ETN) were analyzed. Additionally, in order to investigate the influence of non-specific and specific solute–solvent interactions on absorption band shifts in protic solvents the multicomponent linear regression with two Kamlet–Taft’s solvatochromic parameters (π* and α) was used. The ν‾A in solvents were also obtained using theoretical calculations with the AM1-SM5.4 method and compared with experimental values. Finally, all the results show that in aprotic solvents there are general dipolarity/polarizability effects, while in protic solvents specific interactions connected with the formation of hydrogen bonds are additionally observed.

One-pot three-component synthesis and photophysical characteristics of novel triene merocyanines.

Novel triene merocyanines, i.e. 1-styryleth-2-enylidene and 4-(1,3,3-trimethylindolin-2-ylidene)but-2-en-1-ylideneindolones are obtained in good to excellent yields in a consecutive three-component insertion Sonogashira coupling–addition sequence. The selectivity of either series is remarkable and has its origin in the stepwise character of the terminal addition step as shown by extensive computations on the DFT level. All merocyanines display intense absorption bands in solution and the film spectra indicate J-aggregation. While 1-styryleth-2-enylideneindolones show an intense deep red emission in films, 4-(1,3,3-trimethylindolin-2-ylidene)but-2-en-1-ylideneindolones are essentially nonemissive in films or in the solid state. TD-DFT computations rationalize the charge-transfer nature of the characteristic broad long-wavelength absorptions bands.

Long wavelength, very long wavelength and narrow-band long-/very-long wavelength two-color type-Ⅱ InAs/GaSb superlattice photodetectors

We have demonstrated a long wavelength (LW), a very-long wavelength (VLW) and a narrow-band two-color LW/VLW photodetectors using type-Ⅱ InAs/GaSb superlattice (SL) materials. For all the detection wavelengths, very high-quality type-Ⅱ InAs/GaSb SL materials have been grown by molecular beam epitaxy. For the LW device, at 77 K, the achieved 50% cutoff wavelength is 9.6 mm and the maximum response is at 7.7 mm with the responsivity of 3.2 A/W. For the VLW device, at 77 K, the 50% cutoff wavelength is 14.5 mm and the corresponding quantum efficiency is 14%. The Johnson noise limited detectivity D * is 4.3×109 cm Hz1/2 W-1 at 14.5 mm. For the first time, we demons- trate a narrow-band two-color detector using type-Ⅱ InAs/GaSb SL strctures. The LW/VLW two-color detector is a two-terminal device and the detection is achieved by changing the bias polarity. The device responds to the LW range when the bias voltage is smaller than 0 V while it works for the VLW range when the bias voltage is larger than 40 mV. Concretely, at 77 K, the 50% cutoff wavelength is 10 mm when the bias voltage is -0.1 V, and is 16 mm when the bias voltage is 40 mV. The achieved dl / l is 44% for the LW photoresponse and is 46% for the VLW photoresponse. The spectral crosstalk of the VLW band to the LW band is 9.9% while that of the LW band to the VLW band is 11.8%.