Effective Manipulation of the Electronic Effects and Its Influence on the Emission of 5-Substituted Tris(8-quinolinolate) Aluminum(III) Complexes

Optical Property Control by the Interligand Charge Transfer Excited State in Brominated Homoleptic and Heteroleptic Aluminum Dinuclear Triple-Stranded Helicates

The utilization of aluminum, an abundant and inexpensive element, for the synthesis of novel functional complexes is extremely important, but the design and control of photofunctionality are still unexplored. In this study, we focused on our previously developed dinuclear triple-stranded helicates incorporating two aluminum ions (ALPHY) to synthesize both homoleptic and heteroleptic complexes with bromine atoms at the 3-position of the pyrrole moiety in the Schiff base ligands. The brominated Schiff base ligands were reacted with AlCl3 to synthesize homoleptic complexes, while different ligands were mixed to prepare heteroleptic complexes. Single-crystal X-ray structural analysis revealed the structures of these novel complexes. We found that increasing the degree of bromination resulted in a tunable emission color, shifting progressively from 550 (yellow) to 566 nm (orange). Optical resolution of the complexes facilitated the observation of mirror-image circular dichroism and circularly polarized luminescence. Furthermore, employing ultrafast spectroscopy techniques, we have elucidated that the optical properties are governed by the interligand charge transfer (ILCT) among the three ligands. The formation of heteroleptic complexes induces the ILCT state even in nonpolar environments, thereby accelerating nonradiative decay and intersystem crossing. These findings mark significant advancements in photofunctional materials based on multinuclear complexes.

Unraveling the Remarkable Influence of Substituents on the Emission Variation and Circularly Polarized Luminescence of Dinuclear Aluminum Triple-Stranded Helicates

This study explored the development of functional dyes using aluminum, focusing on aluminum-based dinuclear triple-stranded helicates, and examined the effects of substituent variations on their structural and optical properties. Key findings revealed that the modification of methyl groups to the pyrrole positions significantly extended the conjugation system, resulting in a red shift in the absorption and emission spectra. Conversely, the modification of methyl groups at the methine positions due to steric hindrances increased the torsion angle of the ligands, leading to a blue shift in the absorption and emission spectra. A common feature across all complexes was that in the excited state, one of the three ligands underwent significant structural relaxation. This led to a pronounced Stokes shift and minimal spectra overlap with high photoluminescence behaviors. Moreover, our research extended to the optical resolution of the newly synthesized complexes by analyzing the chiroptical properties of the resulting enantiomers, including their circular dichroism and circularly polarized luminescence. These insights offer valuable contributions to the design and application of novel aluminum-based functional dyes, potentially influencing a range of fields, from materials science to optoelectronics.

A Highly Fluorescent Dinuclear Aluminium Complex with Near‐Unity Quantum Yield**

The high natural abundance of aluminium makes the respective fluorophores attractive for various optical applications, but photoluminescence quantum yields above 0.7 have yet not been reported for solutions of aluminium complexes. In this contribution, a dinuclear aluminium(III) complex featuring enhanced photoluminescence properties is described. Its facile one‐pot synthesis originates from a readily available precursor and trimethyl aluminium. In solution, the complex exhibits an unprecedented photoluminescence quantum yield near unity (Φ_absolute 1.0±0.1) and an excited‐state lifetime of 2.3 ns. In the solid state, J‐aggregation and aggregation‐caused quenching are noted, but still quantum yields of 0.6 are observed. Embedding the complex in electrospun non‐woven fabrics yields a highly fluorescent fleece possessing a quantum yield of 0.9±0.04.

A Simple Procedure for Synthesis of Biological Active 4-oxo-4-(quinolin-8-yloxy)but-2-enoic acid

The article is devoted to research on the synthesis of hydroxyquinoline derivative based on 8-oxyquinoline and maleic anhydride. Analysis of available literature was carried out, some drugs were found that are produced based on hydroxyquinoline derivatives and have antiprotozoal, antimicrobial and antiseptic effects, used alone or in combination with other active substances. A technique has been developed for the synthesis of a new derivative in the medium of petroleum distillate using sulfuric acid as a catalyst. A water-soluble ester of 8-oxyquinoline and maleic acid was obtained in good yield (95%), the structure of which was established based on UV, IR and NMR spectroscopy. By analogy with other oxyquinoline derivatives and the results of prediction bioactivity in the PASS program, the obtained derivative may be characterized by antifungal (antiseborrheic) action. It was determined its antibacterial properties at a concentration of 20.0–10.0 mg/cm3 as well as a significant antioxidant activity which is a useful biological property to expand the range of its application.

Tuning of bandgaps and emission properties of light-emitting diode materials through homogeneous alloying in molecular crystals

Alloy formation is ubiquitous in inorganic materials science, and it strongly depends on the similarity between the alloyed atoms. Since molecules have widely different shapes, sizes and bonding properties, it is highly challenging to make alloyed molecular crystals. Here we report the generation of homogenous molecular alloys of organic light emitting diode materials that leads to tuning in their bandgaps and fluorescence emission. Tris(8-hydroxyquinolinato)aluminium (Alq₃) and its Ga, In and Cr analogues (Gaq₃, Inq₃, and Crq₃) form homogeneous mixed crystal phases thereby resulting in binary, ternary and even quaternary molecular alloys. The M_xM′_(1−x)q₃ alloy crystals are investigated using X-ray diffraction, energy dispersive X-ray spectroscopy and Raman spectroscopy on single crystal samples, and photoluminescence properties are measured on the exact same single crystal specimens. The different series of alloys exhibit distinct trends in their optical bandgaps compared with their parent crystals. In the Al_xGa_(1−x)q₃ alloys the emission wavelengths lie in between those of the parent crystals, while the Al_xIn_(1−x)q₃ and Ga_xIn_(1−x)q₃ alloys have red shifts. Intriguingly, efficient fluorescence quenching is observed for the M_xCr_(1−x)q₃ alloys (M = Al, Ga) revealing the effect of paramagnetic molecular doping, and corroborating the molecular scale phase homogeneity.

Multicomponent molecular alloy crystals exhibit intriguing effects of tuning and quenching in their photoluminescence, suggesting ‘alloy-crystal engineering’ as a useful design strategy for molecular functional materials.

Synthesis and Photophysical Properties of a Series of Dimeric Indium Quinolinates

A novel class of quinolinol-based dimeric indium complexes (1-6) was synthesized and characterized using ¹H and ¹³C(¹H) NMR spectroscopy and elemental analysis. Compounds 1-6 exhibited typical low-energy absorption bands assignable to quinolinol-centered π-π* charge transfer (CT) transition. The emission spectra of 1-6 exhibited slight bathochromic shifts with increasing solvent polarity (p-xylene < tetrahydrofuran (THF) < dichloromethane (DCM)). The emission bands also showed a gradual redshift, with an increase in the electron-donating effect of substituents at the C5 position of the quinoline groups. The absolute emission quantum yields (Φ_PL) of compounds 1 (11.2% in THF and 17.2% in film) and 4 (17.8% in THF and 36.2% in film) with methyl substituents at the C5 position of the quinoline moieties were higher than those of the indium complexes with other substituents.

Full Visible Spectrum and White Light Emission with a Single, Input-Tunable Organic Fluorophore

The blue emission of M2biQ can be tuned to specific wavelengths throughout the visible region by changing the identity of the cation it interacts with. These optical properties are observed in MeCN solution and the solid state. White light is obtained in MeCN by using either the proper ratio of zinc ions or acid. Thus, M2biQ acts as a nearly universal emitter (λem = 468-690 nm) with large Stokes shifts (116-306 nm, Δν̃ = 7,042-11,823 cm-1). Full spectral profiles as well as quantum yields, lifetimes, and the crystal structures of key RGB and yellow emitters are reported. Emission wavelengths correlate with cationic radius, and TD-DFT calculations show that, for 1:1 complexes, the smaller the ion, the shorter the N-cation bond, and the greater the bathochromic emission shift.

Absorption and emission properties of 5-phenyl tris(8-hydroxyquinolinato) M(III) complexes (M = Al, Ga, In) and correlations with molecular electrostatic potential

Substituent effect for a series of 5-phenyl tris(8-hydroxyquinolinato) M(III) complexes (Mq3) of aluminum, gallium, and indium are investigated using density functional theory (DFT) for the ground state properties and the time-dependent version of DFT (TDDFT) for their absorption and emission properties. A comparison between the ground state energy of mer and fac isomers of all the complexes revealed that the mer configuration is always more stable than fac. The substituent effect is significantly reflected at the fluorescence maximum (λ_F ) values whereas the effect is moderate at the absorption maximum (λ_abs ) values. The molecular electrostatic potential (MESP) at the metal center (V_M ) and the most electron rich region indicated by MESP minimum (V_min ), located at the oxygen of phenoxide ring exhibit excellent correlations with the λ_F and Stokes shift (λ_F -λ_abs ) values. The study suggests the use of Stokes shift as an experimental quantity to measure the excited state substituent effect while the V_min or V_M emerge as theoretical quantities to measure the same.

Regulating structural dimensionality and emission colors by organic conjugation between SmIII at a fixed distance

The conjugation of bridging bis(diphenylphosphine oxide) alkane or arene ligands was found to control the structural dimensionality and the emission color of complexes from reactions with SmIII(hfac)3(H2O)2 (hfac- = hexafluoroacetylacetonato) while retaining the SmSm distances. Bis(diphenylphosphine oxide)-1,4-butane (L1) affords a one-dimensional (1D) ribbon {Sm(hfac)3(L1)}∞ (1) that emits red color, while bis(diphenyl-phosphinoyl)-1,4-benzene (L2) results in a two-dimensional (2D) network {Sm(hfac)2(CF3COO)(L2)3}∞ (2) and near-white emission, but bis(diphenyl-phosphinoyl)-9,10-anthracene (L3) forms a zero-dimensional (0D) cyclic structure {Sm(hfac)3(L3)}2 (3) with strong ππ interactions that emit green color. Noticeably, the conjugation change is accompanied by a configurational change of coordination from trans for 1 and 2 to cis for 3. The color change is associated with the superposition of ligand and Sm based electronic band energies and their intensities. Such white light emission by a single compound having contributions from different building components is quite rare.

Salen-indium/triarylborane triads: synthesis and ratiometric emission-colour changes by fluoride ion binding

Salen-based indium triads, [{(3-tBu)2-(5-Mes2B)2-salen}In-Me] (1) and [{(3-tBu)2-(5-Mes2Bphenyl)2-salen}In-Me] (2), bearing triarylborane (TAB) units were prepared and fully characterised by NMR spectroscopy and elemental analysis. The major absorption bands of 1 and 2 appeared in the region centred at 347 nm and 374 nm, respectively, and the intense emission spectra were observed in the sky blue (λem = 491 nm for 1) and bluish-green (λem = 498 nm for 2) regions, respectively. The solvatochromism effects in various organic solvents and computational calculation results strongly suggested that these absorption and emission features are mainly attributed to intramolecular charge transfer (ICT) transitions between the salen ligand moieties and the TAB units. Furthermore, UV-vis and photoluminescence (PL) titration experiments by the addition of fluoride anions demonstrated ratiometric quenching patterns in both the absorption and emission spectra, indicating that binding of the fluoride anion to the boron centres interrupts these ICT transitions in each compound. Interestingly, both triads exhibited a gradual red-shifted response in each emission spectrum upon the addition of the fluoride anions, resulting in a dramatic colour-change to yellow. The computational calculation results of the S1 states revealed that these emission-colour change properties arise from the elevation of HOMO levels, which are mainly localised on the TAB moieties, resulting from the fluoride anion binding to the borane centres.

Si(bzimpy)2 – a hexacoordinate silicon pincer complex for electron transport and electroluminescence

We demonstrate the feasibility of hexacoordinate silicon complexes with dianionic pincer ligands as electron transport and electroluminescent components of organic electronic devices.

A highly sensitive and selective chemosensor for Pb2+ based on quinoline–coumarin

In this study, a highly sensitive and selective fluorescent chemosensor, ethyl(E)-2-((2-((2-(7-(diethylamino)-2-oxo-2H-chromene-3-carbonyl)hydrazono)methyl)quinolin-8-yl)oxy)acetate (1), was synthesized and characterized by ¹H NMR, ¹³C NMR and ESI-MS. Sensor 1 showed an “on–off” fluorescence response to Pb²⁺ with a 1 : 1 binding stoichiometry in CH₃CN/HEPES buffer medium (9 : 1 v/v). The detection limit of sensor 1 to Pb²⁺ was determined to be 0.5 μM, and the stable pH range for Pb²⁺ detection was from 4 to 8.

A highly sensitive and selective fluorescent chemosensor 1 was synthesized and used for naked eye detection of Pb²⁺.

Understanding M-ligand bonding and mer-/fac-isomerism in tris(8-hydroxyquinolinate) metallic complexes

Tris(8-hydroxyquinolinate) metallic complexes, Mq3, are one of the most important classes of organic semiconductor materials. Herein, the nature of the chemical bond in Mq3 complexes and its implications on their molecular properties were investigated by a combined experimental and computational approach. Various Mq3 complexes, resulting from the alteration of the metal and substitution of the 8-hydroxyquinoline ligand in different positions, were prepared. The mer-/fac-isomerism in Mq3 was explored by FTIR and NMR spectroscopy, evidencing that, irrespective of the substituent, mer- and fac-are the most stable molecular configurations of Al(iii) and In(iii) complexes, respectively. The relative M-ligand bond dissociation energies were evaluated experimentally by electrospray ionization tandem mass spectrometry (ESI-MS-MS), showing a non-monotonous variation along the group (Al > In > Ga). The results reveal a strong covalent character in M-ligand bonding, which allows for through-ligand electron delocalization, and explain the preferred molecular structures of Mq3 complexes as resulting from the interplay between bonding and steric factors. The mer-isomer reduces intraligand repulsions, being preferred for smaller metals, while the fac-isomer is favoured for larger metals where stronger covalent M-ligand bonds can be formed due to more extensive through-ligand conjugation mediated by metal "d" orbitals.

Xanthurenic acid: a natural ionophore with high selectivity and sensitivity for potassium ions in an aqueous solution

Synopsis: A well-known tryptophan metabolite, xanthurenic acid, a natural non-fluorescent intermediate siderophore, showed a very selective turn-on response to K⁺ over other competing metal ions and the detection limit of this natural ionophore was found to be 53 nM at physiological pH.

Photophysical tuning of the aggregation-induced emission of a series of para-substituted aryl bis(imino)acenaphthene zinc complexes

Bis(imino)acenaphthene (BIAN) zinc complexes with para-substituted aryl groups have been synthesized and investigated from the standpoint of their photophysical properties. Each complex was found to be nonemissive in solution. However, complexes 1-6 turned out to be emissive in the solid state, while complexes 7 and 8 remained nonemissive. The emissions for complexes 1-8 displayed color tunability ranging from red-yellow. A detailed crystallographic study of the "as-synthesized" structures revealed a distinct difference in the crystal packing environments of the emissive and nonemissive complexes. Furthermore, a solvatomorphic study provided further emission tunability via changes in the crystal packing environments of each solvatomorph. Lastly, TD-DFT calculations were performed in order to investigate the effect of different para-substituents on the flanking aryl rings of the BIAN ligand.

Charge carrier mobility and electronic properties of Al(Op)3: impact of excimer formation

We have studied the electronic properties and the charge carrier mobility of the organic semiconductor tris(1-oxo-1H-phenalen-9-olate)aluminium(III) (Al(Op)3) both experimentally and theoretically. We experimentally estimated the HOMO and LUMO energy levels to be -5.93 and -3.26 eV, respectively, which were close to the corresponding calculated values. Al(Op)3 was successfully evaporated onto quartz substrates and was clearly identified in the absorption spectra of both the solution and the thin film. A structured steady state fluorescence emission was detected in solution, whereas a broad, red-shifted emission was observed in the thin film. This indicates the formation of excimers in the solid state, which is crucial for the transport properties. The incorporation of Al(Op)3 into organic thin film transistors (TFTs) was performed in order to measure the charge carrier mobility. The experimental setup detected no electron mobility, while a hole mobility between 0.6 × 10(-6) and 2.1 × 10(-6) cm(2)·V(-1)·s(-1) was measured. Theoretical simulations, on the other hand, predicted an electron mobility of 9.5 × 10(-6) cm(2)·V(-1)·s(-1) and a hole mobility of 1.4 × 10(-4) cm(2)·V(-1)·s(-1). The theoretical simulation for the hole mobility predicted an approximately one order of magnitude higher hole mobility than was observed in the experiment, which is considered to be in good agreement. The result for the electron mobility was, on the other hand, unexpected, as both the calculated electron mobility and chemical common sense (based on the capability of extended aromatic structures to efficiently accept and delocalize additional electrons) suggest more robust electron charge transport properties. This discrepancy is explained by the excimer formation, whose inclusion in the multiscale simulation workflow is expected to bring the theoretical simulation and experiment into agreement.

Tuning of the colour and chemical stability of model boranils: a strong effect of structural modifications

An improved approach to luminescent diphenylborinic complexes with functionalized salicydeneaniline ligands was developed. A strong effect of structural modifications on their stability and optical properties was established.

Reticular three-dimensional 3d–4f frameworks constructed through substituted imidazole-dicarboxylate: syntheses, luminescence and magnetic properties study

Series of heteronuclear metal organic frameworks (HMOF) combination of lanthanide and Zn/Co ions based on a rigid substituted imidazoledicarboxylic acid ligand have been successfully isolated and characterized systematically.

Synthesis, characterization and DFT calculation of 4-fluorophenyl substituted tris(8-hydroxyquinoline)aluminum(III) complexes

New 4-fluorophenyl substituted 8-hydroxyquinoline derivatives, 5-(4-fluorophenyl)quinolin-8-ol and 5,7-bis(4-fluorophenyl)quinolin-8-ol, were synthesized and characterized by spectroscopic methods. The aluminum complexes of 5-(4-fluorophenyl)quinolin-8-ol (AlQF) and of 5,7-bis(4-fluorophenyl)quinolin-8-ol (AlQF2) exhibit strong fluorescence emission centered at 525 nm and 530 nm respectively. The quantum yield of both complexes were enhanced compared to the parent tris(8-hydroxyquinolinato)aluminum(III) complex. Electronic structures and photophysical properties of the new complexes were investigated theoretically by ab initio and density functional theory (DFT) and time dependent DFT (TD-DFT). Geometries of the ground state (S0) and the first excited state (S1) of the new complexes were optimized at the B3LYP/6-31G(d) functional and configuration interaction singles (CIS) method respectively. The aryl substituents were found to contribute significantly to the frontier molecular orbitals (FMOs). We have observed that in both cases the lowest occupied molecular orbital (LUMO) energy decreases while the energy of the highest occupied molecular orbital is slightly increased. The most significant increase was observed for AlQF2.

Spectroscopic study of a synthesized Alq3 end-capped oligothiophene applied in organic solar cells

We report the synthesis and wide spectroscopic studies of an Alq₃ end-capped oligothiophene applied in organic solar cells.

Methyl 2-[(2-chloro-quinolin-3-yl)(hy-droxy)meth-yl]acrylate

There are two independent mol-ecules (A and B) in the asymmetric unit of the title compound, C14H12ClNO3. The mean planes of the methyl ester unit (Cmeth-yl-O-C=O; r.m.s. deviation = 0.051 Å for mol-ecule A and 0.016 Å for mol-ecule B) and the chloro-quilonine ring system (r.m.s. deviation = 0.023 Å for mol-ecule A and 0.014 Å for mol-ecule B) form dihedral angles of 63.5 (1)° in mol-ecule A and 78.1 (1)° in mol-ecule B. The main difference between the two independent mol-ecules is reflected in the (H)O-C-C=C(H2) torsion angle which is -109.7 (2)° in mol-ecule A and 10.6 (2)° in mol-ecule B. An intra-molecular O-H⋯O hydrogen bond is observed in mol-ecule A. In the crystal, mol-ecules A and B are linked into pairs via bifurcated O-H⋯(N,Cl) hydrogen bonds and a weak C-H⋯O hydrogen bond links pairs of mol-ecules into chains along [100].