Intense Fluorescence Band Research Articles

A Chalcone Based Novel Fluorescent Nanoprobe for Selective Detection of Al3+ Ion in Aqueous Medium

A chalcone based novel fluorescent organic nanoparticles are prepared by reprecipitation method. The Dynamic Light Scattering histogram shows narrow particle size distribution and the average diameter of particle is 37.2 nm. The Scanning Electron Microphotograph shows the fibre like morphology. The blue shifted UV-visible spectra. The significant large Stokes shift of Trans-3-(9-Anthryl)-1-phenylprop-2-en-1-one nanoparticles (APPONPs) in aqueous suspension as compared with that of a dilute solution of Trans-3-(9Anthryl)-1-phenylprop-2-en-1-one (APPO) in acetone indicates H- aggregation of molecules by π- π stacking. An intense fluorescence band peaking at 556 nm is attributed to Aggregation Induced Enhanced Emission (AIEE) by direct excitation of APPONPs. The binding of Al 3+ increased the fluorescence of APPONPs while other cations actually decreases the fluorescence. The fluorescence enhancement of APPONPs by Al 3+ was discussed on the basis of hard and soft acid and base (HSAB) theory. The enhancement of APPONPs emission is linear in the concentration range 0-80 μM of Al3+. The enhancement of fluorescence of APPONPs results obeys the straight line equation with RSD = 0.9879%. The present method has Limit of Detection (LOD)= 1.148 μM of Al 3+ which is lower than the LOD reported for Al 3+ by using other methods like colorimetry, potentiometry. This study was succesfully applied to develop fluorimetric method for determination of Al3+ in environmental samples. The method affords fairly practical and economical approach.

Highly Fluorescent Thienoviologen‐Based Polymer Gels for Single Layer Electrofluorochromic Devices

A highly fluorescent electrofluorochromic gel with quantum yields as high as 67% is prepared by incorporating the thienoviologen fluorophore 4,4′‐(2,2′‐bithiophene‐5,5′‐diyl)bis(1‐nonylpridinium)bistriflimide into a polymeric matrix. The fluorescent emission spectrum of the gel at low percentages of thienoviologen shows a strong band at 530 nm. A new intense fluorescence band at 630 nm can be induced by fluorophore aggregation. Single layer electrofluorochromic devices were readily prepared by sandwiching the polymer gels between two indium tin oxide (ITO) electrodes. The fluorescence intensity can be easily modulated between a fluorescent and a quenched state, in a wide visible spectral range, by direct electrochemical reduction of the thienoviologen fluorophore. It exhibits three reduction states, each with different emission properties. The reversible interconversion among these states leads to a high electrofluorochromic stability of the device, exhibiting switching times of a few seconds and, to the best of our knowledge, the highest contrast ratio (337).

Effects of added phthalate plasticizers on photodegradation of irradiated poly (α-methylstyrene) films

Abstract The effects of UV irradiation and blending on the stability of poly (α-methylstyrene) (PαMS) in solid films were studied at different intervals of irradiation time in the presence of air, by absorption, emission and Fourier transform infrared (FT-IR) spectroscopy. The increase in irradiation time caused an increase in the intensity of the absorption band of the polymer, and an increase in the intensity of absorption of a new broad band at a longer wavelength, thus indicating the possibility of photodegradation of polymeric chains. The influence of added plasticizers, dimethyl terephthalate (DMT), diethyl terephthalate (DET), dibutyl phthalate (DBP), dioctyl phthalate (DOP) and dioctyl terephthalate (DOT) on photoquenching of the polymer fluorescence band was also investigated, and found to increase the photoquenching processes with increase in the amount of added plasticizers. By contrast, the intensity of excimer and monomer fluorescence bands was also found to decrease with increase in irradiation times. These changes may be attributed to the formation of new photoproducts which resulted from the photodegradation and photooxidation of irradiated polymeric chains. In addition, the observed increase in the intensities of the carbonyl and hydroxyl regions of the FT-IR spectra provides evidence for the photooxidation of polymeric chains. The increase in the intensity of some bands and the disappearance of new bands indicate the photodegradation of polymeric chains.

{[Ph4P]2[Cd2(tp)2(Htp)2(H2O)]·3H2O}n and {[Ph4P][Zn(tp)(Htp)]·2H2O}n: Two interesting 2D metal–terephthalate polymeric networks

Two new metal–terephthalate polymeric solids, {[Ph4P]2[Cd2(tp)2(Htp)2(H2O)]·3H2O}n (1) and {[Ph4P][Zn(tp)(Htp)]·2H2O}n (2) (tp=terephthalate, [Ph4P]=tetraphenylphosphonium), are obtained from similar hydrothermal synthesis reactions. Upon the template effect of large bulky [Ph4P]+ cation, the d10 transition metal centers are bridged by tp ligands to form an interesting 2D undulating lamellar host network for 1 and a 2D square-grid lamellar host network for 2, respectively. Both compounds exhibit intense fluorescent emission bands at 434nm (λexc=333nm) for 1 and 420nm (λexc=350nm) for 2 in the solid state at room temperature.

Enhanced 2.7 μm mid-infrared emission and energy transfer mechanism in Er3+/Nd3+ codoped tellurite glass

Nd3+ was introduced into Er3+ doped tellurite glass with composition of TeO2Nb2O5ZnONa2O to improve the 2.7μm band fluorescence upon the excitation of 800nm LD. The DSC curve and Raman spectrum were measured to characterize the thermal stability and vibration nature of glass host. The absorption spectra, visible, near- and mid-infrared fluorescence emission spectra were measured to evaluate the effects of Nd3+ introduction on the spectroscopic properties especially the 2.7μm band fluorescence of Er3+. It is shown that the prepared tellurite glass exhibits a large glass transition temperature and no obvious crystallization peak is observed in the measured temperature range of 200–550°C. Moreover, the introduction of Nd3+ significantly improves the 2.7μm band fluorescence intensity through joint energy transfer processes between the relevant excited levels of Er3+ and Nd3+, and the energy transfer mechanisms are further investigated in detail by calculating energy transfer micro-parameters and efficiency. The excellent thermal stability and strong 2.7μm fluorescence emission aroused by adopting codoping scheme indicate that the prepared Er3+/Nd3+ codoped tellurite glass is a potential glass medium applied for the 2.7μm mid-infrared band lasers.

Cut Site Selection by the Two Nuclease Domains of the Cas9 RNA-guided Endonuclease

Cas9, the RNA-guided DNA endonuclease from the CRISPR-Cas (clustered regularly interspaced short palindromic repeat-CRISPR-associated) system, has been adapted for genome editing and gene regulation in multiple model organisms. Here we characterize a Cas9 ortholog from Streptococcus thermophilus LMG18311 (LMG18311 Cas9). In vitro reconstitution of this system confirms that LMG18311 Cas9 together with a trans-activating RNA (tracrRNA) and a CRISPR RNA (crRNA) cleaves double-stranded DNA with a specificity dictated by the sequence of the crRNA. Cleavage requires not only complementarity between crRNA and target but also the presence of a short motif called the PAM. Here we determine the sequence requirements of the PAM for LMG18311 Cas9. We also show that both the efficiency of DNA target cleavage and the location of the cleavage sites vary based on the position of the PAM sequence.

Silver nanoparticles enhanced 1.53 µm band fluorescence of Er3+/Yb3+ codoped tellurite glasses

The silver nanoparticles (NPs) was introduced into the Er3+/Yb3+ codoped tellurite glasses with composition of TeO2–ZnO to improve the 1.53µm band fluorescence of Er3+ and the thermal stability of glass host. The UV–Vis–NIR absorption spectra, 1.53µm band fluorescence spectra and fluorescence decaying curves, the differential scanning calorimeter (DSC) curves, X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) images of glass samples were characterized to investigate the effect of silver NPs on the fluorescence properties of Er3+, thermal stability and structure behavior of glass host. It is shown that the Er3+/Yb3+ codoped tellurite glass emits intense 1.53µm band fluorescence with peak wavelength located at about 1532nm under the 980nm excitation. The introduction of silver NPs further improves the fluorescence intensity of Er3+ which is attributed to the enhanced local electric field effect induced by localized surface Plasmon resonance (LSPR) of silver NPs and the possible energy transfer from silver NPs to Er3+. An improvement by about 62% of 1.53µm band fluorescence intensity was found in the studied Er3+/Yb3+ codoped tellurite glass containing 0.5mol% amount of AgNO3. In addition, the thermal stability of glass host increases with the introduction of silver NPs while the glass structure maintains the amorphous nature. The present results indicate that the prepared Er3+/Yb3+ codoped tellurite glass with an appropriate amount of silver NPs has good prospect as a gain medium applied for 1.53µm band broad and high-gain erbium-doped fiber amplifiers (EDFAs).

Fluorescence behavior of cis-methyl orange stabilized in cationic premicelles

The cis-isomer of methyl orange (MO), stabilized in cationic premicelles, has been found to be fluorescence active when excited at wavelength ⩽270nm. An intense fluorescence band with maximum at 575nm along with a broad moderate intensity band in the range of 370–530nm and a low intensity band at 361nm have been observed. The major band at 575nm has been attributed to S1→S0 (n–π*) fluorescence unlike the other azobenzenes where the S2→S0 (π–π*) fluorescence is usually reported. UV–Vis spectral and surface tension study indicate that the dye exists in the trans form in dye-surfactant ionpair (DSIP) at very dilute concentrations of the surfactant. But the polar cis-isomer is stabilized by micellization of the DSIPs as the concentration of the surfactant is increased. The fluorescence and hence the cis-isomer again disappear when normal micelles are formed above the normal CMC of the surfactant. It has been suggested that the symmetry forbidden S1→S0 (n–π*) transition of MO becomes allowed due to the formation of the twisted cis-form. TD-DFT calculations have been used as an auxiliary tool to identify the possible structures and electronic transitions responsible for the specific absorption and fluorescence properties of MO observed in presence of premicellar cationic surfactants.

Laser-Induced Point Defects in Fused Silica Irradiated by UV Laser in Vacuum

High-purity fused silica irradiated by third harmonic of the Nd:YAG laser in vacuum with different laser pulse parameters was studied experimentally. Laser-induced defects are investigated by UV spectroscopy, and fluorescence spectra and correlated to the structural modifications in the glass matrix through Raman spectroscopy. Results show that, for laser fluence below laser-induced damage threshold (LIDT), the absorbance and intensity of fluorescence bands increase with laser energies and/or number of laser pulses, which indicates that laser-induced defects are enhanced by laser energies and/or number of laser pulses in vacuum. The optical properties of these point defects were discussed in detail.

Structure and spectroscopic properties of Er3+/Ce3+ co-doped TeO2-Bi2O3-TiO2 glasses modified with various WO3 contents for 1.53 μm emission

The Er3+/Ce3+ co-doped tellurite-based glasses (TeO2-Bi2O3-TiO2) modified with various WO3 contents are prepared using conventional melt-quenching technique. The X-ray diffraction (XRD) patterns and Raman spectra of glass samples are measured to investigate the structures. The absorption spectra, the up-conversion emission spectra, the 1.53 μm band fluorescence spectra and the lifetime of Er3+:4I13/2 level are measured, and the amplification quality factors of Er3+ are calculated to evaluate the effect of WO3 contents on the 1.53 μm band spectroscopic properties. With the introduction of WO3, it is found that the prepared tellurite-based glasses maintain the amorphous structure, while the 1.53 μm band fluorescence intensity of Er3+ is improved evidently, and the fluorescence full width at half maximum (FWHM) is broadened accordingly. In addition, the prepared tellurite-based glass samples have larger bandwidth quality factor than silicate and germanate glasses. The results indicate that the prepared Er3+/Ce3+ co-doped tellurite-based glass with a certain amount of WO3 is an excellent gain medium applied for the 1.53 μm band Er3+-doped fiber amplifier (EDFA).

Effect of B2O3 on the spectroscopic properties in Er3+/Ce3+ co-doped tellurite-niobium glass

The high phonon energy oxide of B2O3 is introduced into the Er3+/Ce3+ co-doped tellurite-niobium glasses with composition of TeO2-Nb2O5-ZnO-Na2O. The absorption spectra, 1.53 μm band fluorescence spectra, fluorescence lifetime and Raman spectra of Er3+ in glass samples are measured together with the calculations of Judd-Ofelt spectroscopic parameter, stimulated emission and absorption cross-sections, which evaluate the effect of B2O3 on the 1.53 μm band spectroscopic properties of Er3+. It is shown that the introduction of an appropriate amount of B2O3 can further improve the 1.53 μm band fluorescence intensity through an enhanced phonon-assisted energy transfer (ET) between Er3+/Ce3+ ions. The results indicate that the prepared Er3+/Ce3+ co-doped tellurite-niobium glass with an appropriate amount of B2O3 is a potential gain medium for the 1.53 μm bandbroad erbium-doped fiber amplifier (EDFA).

Enhancement of the 1.53 μm fluorescence and energy transfer in Er3+/Yb3+/Ce3+ tri-doped WO3 modified tellurite-based glass

For the first time, the WO3 oxide with relatively high phonon energy was introduced into the Er3+/Yb3+/Ce3+ tri-doped tellurite-based glasses with composition of TeO2Bi2O3TiO2 to improve the 1.53μm band fluorescence emission. The X-ray diffraction (XRD) curves, Raman spectra, absorption spectra and 1.53μm band fluorescence spectra were measured, along with the Judd–Ofelt intensity parameters, stimulated emission and absorption cross-sections, and radiative quantum efficiencies were calculated to evaluate the effects of WO3 amount on the glass structure and spectroscopic properties especially the 1.53μm band fluorescence. It is shown that the introduction of an appropriate amount of WO3 oxide can further improve the 1.53μm band fluorescence intensity through an enhanced phonon-assisted energy transfer between Er3+/Ce3+ ions and the energy transfer mechanisms between Er3+/Yb3+ (Er3+/Ce3+) ions are investigated quantitatively in detail by calculating energy transfer microparameters and phonon contribution ratios. The results indicate that the prepared Er3+/Yb3+/Ce3+ tri-doped tellurite glass with an appropriate amount of WO3 oxide is a potential gain medium applied for the 1.53μm band broad and high-gain EDFA.

Synthesis, photophysical and electrochemical properties of aza-boron-diquinomethene complexes

A series of aza-boron-diquinomethene (aza-BODIQU) complexes with different aryl-substituents (B1–B6) were synthesized and characterized. Their photophysical properties were investigated systematically via spectroscopic and theoretical methods. All complexes exhibit strong 1π–π* absorption bands and intense fluorescent emission bands in the visible spectral region at room temperature. The fluorescence spectra in solution show the mirror image features of the S0→S1 absorption bands, which can be assigned to the 1π–π*/1ICT (intramolecular charge transfer) emitting states. Except for B6, all complexes exhibit high photoluminescence quantum yields (ΦPL = 0.47–0.93). The spectroscopic studies and theoretical calculations indicate that the photophysical properties of these aza-BODIQUs can be tuned by the appended aryl-substituents, which would be useful for rational design of boron–fluorine complexes with high emission quantum yield for organic light-emitting applications.

Studies on the inclusion complexation between intramolecular charge transfer probe trans-ethyl p-(dimethylamino) cinamate and β-cyclodextrin in presence of ionic and nonionic surfactants

The intramolecular charge transfer (ICT) fluorescence of trans-ethyl p-(dimethylamino) cinamate (EDAC) is used to monitor the complexation behavior of this probe with surfactants/β-CD by steady state and picosecond time-resolved fluorescence spectroscopy. The ICT fluorescence band intensity was found to increase with concomitant blue shift in presence of surfactants/β-CD. The encapsulation behavior was further characterized by increase in emission yield as well as lifetime values. Detailed analyses of the spectroscopic data indicate that the probe forms 1:1 complex with β-CD in aqueous medium. However, in presence of surfactants, 1:1 complex is formed below the critical micelle concentration (cmc) value; whereas, 1:2 complexes are formed under fully micellized condition.

Influence of WO3 on the spectroscopic properties and thermal stability of Er3+/Ce3+ codoped tellurite glasses

The WO3 oxide was introduced into the Er3+/Ce3+ codoped tellurite glasses with the composition of TeO2ZnONa2O, and the absorption spectra, fluorescence emission spectra, fluorescence lifetimes, Raman spectra, XRD and DSC curves of glass samples were measured and investigated, respectively, to evaluate the effect of WO3 component on the 1.53μm band spectroscopic properties of Er3+ and thermal stability of glass hosts. It is shown that the introduction of WO3 component can significantly improve the 1.53μm band fluorescence intensity through an enhanced phonon-assisted energy transfer between Er3+ and Ce3+ ions and the total quantum efficiency corresponding to the 4I13/2→4I15/2 transition reveals a similar increasing trend. The introduction of WO3 component is also beneficial to obtain a large fluorescence FWHM, peak stimulated emission cross-section σep and amplification quality factors of σep×FWHM and σep×τm. Furthermore, the thermal stability of glass hosts increases with the content of WO3 component. The results indicate that the prepared Er3+/Ce3+ codoped tellurite glass containing WO3 oxide is a potential gain medium applied for 1.53μm band broad and high-gain EDFA.

Improvement of 1.53 μm band fluorescence and energy transfer in Er3+/Ce3+ codoped tellurite glasses

The high phonon-energy oxide of B2O3 was introduced into the Er3+/Ce3+ codoped tellurite glasses with composition of TeO2–ZnO–Na2O to improve the 1.53μm band fluorescence intensity of Er3+ and thermal stability of glass hosts. To evaluate the effect of B2O3 component on the fluorescence properties of Er3+ and thermal stability of glass hosts, the absorption spectra, upconversion emission spectra, fluorescence emission spectra, fluorescence lifetimes, Raman spectra and differential scanning calorimeter (DSC) curves of glass samples were measured and investigated, respectively. It is shown that the introduction of an appropriate amount of B2O3 component can further improve the 1.53μm band fluorescence intensity through an enhanced phonon-assisted energy transfer between Er3+ and Ce3+ ions, and the energy transfer mechanism is investigated quantitatively in detail by calculating energy transfer micro-coefficients and phonon contributions. Furthermore, the thermal stability of glass hosts increases with the B2O3 component amount, and meanwhile relevant spectroscopic parameters and quantum transition efficiencies of Er3+ are calculated and analyzed using Judd–Ofelt theory. The present results indicate that the prepared Er3+/Ce3+ codoped tellurite glass with an appropriate amount of B2O3 component has good prospect as a gain medium applied for 1.53μm band broad and high-gain EDFA.

The 1.53 μm spectroscopic properties and thermal stability in Er3+/Ce3+ codoped TeO2–WO3–Na2O–Nb2O5 glasses

Er3+/Ce3+ codoped tellurite-based glasses with composition of TeO2–WO3–Na2O–Nb2O5 were prepared by high-temperature melt-quenching technique and a detailed study of the 1.53μm band spectroscopic properties and thermal stability was presented in this paper. The absorption spectra, visible upconversion spectra, 1.53μm band fluorescence spectra, fluorescence lifetimes, Raman spectra, differential scanning calorimeter (DSC) and X-ray diffraction (XRD) curves of glass samples were measured and investigated, together with the quantitative calculations and analyses of Judd–Ofelt intensity parameters, stimulated emission and absorption cross-sections, amplification quality factors, energy transfer rates and quantum transition efficiencies. It was found that the prepared glass samples have good thermal stability (Tg>425°C), large Judd–Ofelt intensity parameter (Ω6>0.80×10−20cm2) and bandwidth quality factor (σep×FWHM>360×10−21cm2nm) of Er3+. With the increasing of Ce3+ doped concentration, the visible upconversion emission decreased while the 1.53μm band fluorescence intensity improved significantly due to the enhanced energy transfer of Er3+:4I11/2+Ce3+:2F5/2→Er3+:4I13/2+Ce3+:2F7/2 owing to the moderate phonon energy (∼930cm−1) of glass host, which was beneficial in compensating for the existing energy mismatch between the Er3+:4I11/2→4I13/2 emission and Ce3+:2F5/2→2F7/2 absorption transitions. Compared with the Er3+ single-doped case, the 1.53μm band fluorescence intensity in Er3+/Ce3+ codoped glass sample could increase by about 30%. The results indicate that the prepared tellurite-based glass with a suitable Er3+/Ce3+ codoping concentration is an excellent gain medium applied for broadband EDFA pumped with a 980nm laser diode.

Synthesis, crystal structure, and spectroscopic properties of new stilbazolium salt with enlarged π-conjugated system

A new stilbazolium dye 4-{(E)-2-[4-(dimethylamino)naphthalen-1-yl]ethenyl}-1-methylquinolinium iodide monohydrate (DANSQI) having enlarged π-conjugated system was synthesized and characterized by X-ray diffraction, IR, Raman, UV–Vis, Fluorescence, 1H- and 13C NMR spectroscopy. Quantum chemical calculations were performed to obtain electronic structure and vibrational data, using DFT. The crystals are monoclinic, space group P21/n, with a=8.0751(14), b=25.839(4), c=10.9031(15) Å, V=2141.4(6) Å3, and Z=4 (at 300(2) K). The unit cell contains four molecules of the dye, participating in weak intermolecular interactions. The cation is nearly flat with a deviation of the planarity of 5.08 (1)°. The dye investigated is the first stilbazolium iodide containing water molecule in the solid state therefore the N-dimethylamino group declines significantly from planarity, as indicated by C13N1C2C3 torsion angle of 16.08°. The dye studied shows solvatochromism of 84nm in visible region and very large Stokes shift up to 253nm. The intensity of fluorescence bands strongly depends on solvent polarity.

Synthetic bacteriochlorins with integral spiro-piperidine motifs

A new molecular design incorporates a spiro-piperidine unit in each pyrroline ring of synthetic bacteriochlorins, thereby (1) replacing the previous geminal dimethyl group with a functionally equivalent motif to suppress adventitious dehydrogenation, (2) enabling tailoring of the bacteriochlorin by nitrogen derivatization, and (3) leaving the β-pyrrolic positions available for introduction of auxochromes to tune the spectral properties. Conversion of an N-protected 4-piperidone to the N-protected α,β-unsaturated ketone, Michael reaction with 4-(ethoxycarbonyl)-3-ethyl-2-(2-nitroethyl)pyrrole, and subsequent reductive cyclization provided the spiro-piperidine-1-methyldihydrodipyrrin. Treatment with SeO2 followed by trimethyl orthoformate under acid catalysis converted the 1-methyl group to a 1-(1,1-dimethoxymethyl) motif. Self-condensation of the resulting spiro-piperidine-dihydrodipyrrin-acetal afforded the 5-methoxy- or 5-unsubstituted bacteriochlorin, each bearing two spiro-piperidine units. The spiro-piperidine units were derivatized at the nitrogens by methylation, sulfonylation, acylation, or quaternization; the latter with methyl iodide afforded two dicationic, hydrophilic bacteriochlorins. Altogether, eight spiro-piperidine-bacteriochlorins were prepared. Spectroscopic characterization was carried out in DMF (and in water for the quaternized, 5-methoxybacteriochlorin). Compared to the 5-unsubstituted analogue, the quaternized, 5-methoxybacteriochlorin has in DMF a shorter wavelength of the intense near-infrared absorption band (733 vs. 752 nm) and fluorescence band (739 vs. 760 nm), modestly greater fluorescence yield (0.15 vs. 0.08) and modestly longer lifetime of the lowest singlet excited state (4.7 vs. 3.3 ns). In general, the spiro-piperidinyl moiety does not significantly alter the rate constants or yields of the decay pathways (fluorescence, intersystem crossing, internal conversion) of the lowest singlet excited state of the bacteriochlorin. Taken together, the results describe a new molecular design for tailoring the polarity of near-infrared absorbers.

Ligand dissociation/recoordination in fluorescent ionic zinc–salicylideneimine compounds: synthesis, characterization, photophysical properties, and 1H NMR studies

A series of ionic zinc-salicylideneimine compounds, [HNEt3][Zn(L)Cl2] (L = sal(H)-4-CN, 1; sal(Cl)-4-CN, 2; sal(Br)-4-CN, 3; sal(OMe)-4-CN, 4) and [NEt4][Zn(sal(H)-4-CN)Cl2] (5), have been synthesized and structurally characterized. Compounds 1-5 all display an intense fluorescence band in both solution (methanol, MeOH; acetonitrile, ACN; dimethylsulfoxide, DMSO; dichloromethane, DCM) and solid phases, with a maximum in the region of 515-560 nm and 529-573 nm, respectively. Detailed (1)H NMR and optical spectroscopic studies indicate the occurrence of ligand dissociation and recoordination in 1-4 in solution, leading to an equilibrium between the zinc-salicylideneimine complex species, [Zn(L)Cl2](-), and the salicylideneimine free ligand, HL. The tendency of ligand dissociation is related to the solvent, the concentration, and the substitution of the salicylidene ring. The greatest degree of ligand dissociation is observed for 1-4 when dissolved in noncoordinating, less polar DCM solvent, followed by coordinating, high polar DMSO solvent. The least degree of ligand dissociation occurs in solutions of coordinating, moderately polar MeOH and ACN solvents for 1-3 and 4, respectively. Dilute solutions are likely characterized by the high degree of ligand dissociation, whereas the equilibrium shifts in favor of the complex [Zn(L)Cl2](-) form at higher concentration. Furthermore, the electron-donating methoxy substitution in the salicylidene ring promotes a high tendency for ligand dissociation, while electron-withdrawing chloro and bromo groups cause the reverse tendency. The (1)H NMR spectrum of 5 shows only one set of proton resonances in the aromatic region corresponding to the complex [Zn(sal(H)-4-CN)Cl2](-) species, indicating that the lack of ammonium proton would protect the complex form from ligand dissociation.