Molecular design and application of luminescent materials composed of group 13 elements with an aggregation-induced emission property

Luminescent Alkylaluminium Anthranilates Reaching Unity Quantum Yield in the Condensed Phase

Transition, post-transition and rare earth metal complexes supported by (O,N)- and (N,N)-type ligands dominate organometallic photochemistry. However, despite a vast number of aminobenzoate metal complexes having been reported, and aluminium being globally abundant, alkylaluminium anthranilates have not yet been considered as effective luminophores. Herein, using a family of commercially available ligands composed of anthranilic acid (anth-H2) and its N-substituted derivatives, we report the isolation and characterisation of a series of unique tetrameric chiral-at-metal alkylaluminium anthranilates, [(R'-anth)AlR]4. The resulting compounds are characterised using spectroscopic methods and single-crystal X-ray diffraction to analyse structure-determining factors in the solid state and solution. Moreover, by changing the N-substituents from H to Me and Ph, we have yielded a series of luminophores that exhibit poor-to-excellent performance, providing a [(Ph-anth)AlEt]4 derivative that achieves a unity photoluminescence quantum yield in the condensed phase, which is unprecedented for aluminium complexes.

Stepwise Lighting Up Gold(I)-Thiolate Complexes from AIE Nanoaggregates to AIEE Nanoprobes with a ZIF-8 Shell for Glucose Biosensing

Aggregation-induced emission (AIE) or aggregation-induced emission enhancement (AIEE) has endowed gold species with responsive fluorescent properties, favoring their potential applications in sensing, imaging, and therapy. However, it remains an interesting challenge to fabricate fluorophores with both AIE and AIEE effects. Herein, we presented highly luminescent Au(I) thiolate nanocomplex-based biosensors with Zn2+ induced-AIE and zeolite imidazolate framework (ZIF-8) induced-AIEE effects. The nonemissive monovalent gold-glutathione complexes (AuI-SGs) were obtained to synthesize the core-shell Zn2+/AuI-SG@ZIF-8 composites with strong luminescence via the coordination-assisted self-assembly strategy. By immobilizing GOx on the surface of Zn2+/AuI-SG@ZIF-8, Zn2+/AuI-SG@ZIF-8/GOx biosensors exhibited effective responsiveness to glucose, showing a "turn-off" detection model. The mechanism study revealed that the robust luminescence of Zn2+/AuI-SG@ZIF-8 to glucose sensing was attributed to the acid-stimulated degradation of the probe facilitated by H+ generated from the glucose oxidase (GOx)-catalyzed oxidation process. To achieve noninvasive and intelligent blood glucose detection, the Zn2+/AuI-SG@ZIF-8/GOx-loaded microneedle (MN)-patch fluorescent platform was further developed. The MN-patch-based sensing platform had promising performance for on-needle capture and in situ glucose detection. This study demonstrated a universal and feasible protocol to construct luminescent biosensors for glucose detection and their potential for the development of MN-based analytical devices.

Aggregation-Induced Emission Properties of Atypical Aliphatic-Chain-Linked Siloxanes-Containing Phosphonate Esters

Phosphonate compounds have been proposed as atypical chromophores, but their luminescence properties, especially in combination with flexible aliphatic chains, remain underexplored. In this study, we have synthesized a series of novel siloxane-containing phosphonate esters as organofluorophores through a catalyst-free, one-pot Kabachnik-Fields (K-F) reaction. This reaction involved acetone, cyclohexanone, or cyclopentanone, with siloxanes containing aliphatic amines and phosphonate diesters as reactants. The resulting compounds exhibit blue fluorescence. Fluorescence tests confirmed that all synthesized materials display aggregation-induced emission (AIE) phenomena, with some also exhibiting upconversion. Notably, the luminescence intensity can be modulated by altering the steric hindrance near the phosphonate ester group. Mechanistic studies indicate that the strong blue photoluminescence observed in the aggregated state results from restricted intramolecular motion (RIM) and spatial electronic delocalization. These findings demonstrate that even simple phosphonates, when combined with flexible aliphatic chains, can exhibit significant AIE luminescence properties.

O,S-Chelated bis(pentafluorophenyl)boron and diphenylboron-β-thioketonates: synthesis, photophysical, electrochemical and NLO properties

Boron-β-diketonates are classical emissive materials that have been utilized in various fields, however, boron monothio-β-thioketonates, where one oxygen atom is exchanged for a sulphur atom, have not been explored in detail. To gain a better understanding of this class of materials, we synthesised various aryl substituted monothio-β-diketonate boron complexes with two different aryl substitutions on the boron center and studied their structural, optical and electrochemical properties. Single crystal X-ray analysis revealed that there is considerable deviation in B-O and B-S bond lengths for bis(pentafluorophenyl)boron complexes against diphenyl boron complexes. The bis(pentafluorophenyl)boron complexes have a relatively high absorption coefficient over diphenyl boron complexes. More importantly, a striking difference was observed for the emission behaviour of these compounds. The bis(pentafluorophenyl)boron complexes exhibit weak emission in the solution as well as in the solid state, whereas diphenyl boron complexes do not show any emission in either solution or the solid state. Further, the electrochemical study reveals that diphenyl boron complexes show a reduction potential that is more negative compared to the bis(pentafluorophenyl)boron complexes. The high absorption coefficient of the compounds pointed towards the possibility of high first order hyperpolarizability upon optical excitation, which motivated us to ascertain the nonlinear optical coefficients in the near infrared range, towards applicability of such compounds in optical limiting and switching. The open aperture Z-scan measurements at ultrashort time scales elucidated a few critical features of such compounds towards optical limiting applications.

Thermal deprotonation and condensation of melamine in the presence of indium(III)chloride

The thermal condensation of melamine into molecules melam, melem, and the one-dimensional polymer melon has already been reported. An interesting question arises about the impact of other compounds being present in this process of thermal conversion. The solid-state reaction of C3N6H6 with InCl3 leads to a novel compound featuring deprotonated melam units in a supramolecular assembly, based on the [C12N20H8]4- anion that is interconnected in the structure via N-In-N bonding. The reaction pathway of the formation of this compound is investigated by thermal analysis and the crystal structure of unique (NH4)[(InCl2)3(C12N20H8)]·⅔[InCl3(NH3)] is reported as well as its photoluminescence properties.

N-Vinylthio Phthalimides (N-VTPs): Modular Reagents for Vinylthio AIEgen Transfer

Novel sulfur reagents N-vinylthio phthalimides (N-VTPs) have been employed as modular reagents for vinylthiolation, enabling the construction of aggregation-induced emission (AIE)-active tetraaryldivinyl sulfides (TADVSs) and diarylvinyl sulfides (DAVSs). Notably, TADVSs with sulfur insertion to ethene stators are reported as AIE luminogens (AIEgens) for the first time, and the corresponding photophysical properties and aggregated confirmation have been detailed for the demonstration of the AIE effect. A water-soluble TADVS with a quinolinium salt was prepared for cell imaging.

Excited-State Dynamics in Borylated Arylisoquinoline Complexes in Solution and in cellulo

Two four-coordinate organoboron N,C-chelate complexes with different functional terminals on the PEG chains are studied with respect to their photophysical properties within human MCF-7 cells. Their excited-state properties are characterized by time-resolved pump-probe spectroscopy and fluorescence lifetime microscopy. The excited-state relaxation dynamics of the two complexes are similar when studied in DMSO. Aggregation of the complexes with the carboxylate terminal group is observed in water. When studying the light-driven excited-state dynamics of both complexes in cellulo, i. e., after being taken up into human MCF-7 cells, both complexes show different features depending on the nature of the anchoring PEG chains. The lifetime of a characteristic intramolecular charge-transfer state is significantly shorter when studied in cellulo (360±170 ps) as compared to in DMSO (∼960 ps) at 600 nm for the complexes with an amino group. However, the kinetics of the complexes with the carboxylate group are in line with those recorded in DMSO. On the other hand, the lifetimes of the fluorescent state are almost identical for both complexes in cellulo. These findings underline the importance to evaluate the excited-state properties of fluorophores in a complex biological environment in order to fully account for intra- and intermolecular effects governing the light-induced processes in functional dyes.

Dual-band fluorescence detection of double-stranded DNA with QDs-Mn2+-pefloxacin

By integrating the fluorescence of quantum dots (QDs) and Mn²⁺-pefloxacin mesylate (Mn²⁺-pefloxacin), a new type of dual-band fluorescence biosensor for high-efficiency and sensitive determination of double-stranded DNA (dsDNA) is developed. The biosensor is based on the fluorescence "OFF-ON" mode of both QDs and QDs-Mn²⁺-pefloxacin. The Mn²⁺-pefloxacin complex can quench the QDs fluorescence via photoinduced electron transfer (PET), and its fluorescence is also quenched. Due to the specificity and strong binding affinity of dsDNA for the Mn²⁺-pefloxacin complex, it can break the low fluorescent QDs-Mn²⁺-pefloxacin and restore the fluorescence of QDs and Mn²⁺-pefloxacin complex in their respective bands. Therefore, the dual-band fluorescence quantitative detection of dsDNA by QDs-Mn²⁺-pefloxacin can be achieved, while bovine serum albumin, single-stranded DNA, and bio-related ions do not yield similar results. Furthermore, the possible reaction mechanisms are systematically discussed. The detection limits (3δ/K) of herring sperm (hs) DNA in the fluorescence recovery bands of QDs and Mn²⁺-pefloxacin complex are 0.0142 and 0.0465 μg/mL, respectively. The developed biosensor was used for dsDNA detection in synthetic samples, and desirable results are obtained.

Modulation of Properties by Ion Changing Based on Luminescent Ionic Salts Consisting of Spirobi(boron ketoiminate)

We report development of luminescent ionic salts consisting of the boron ketoiminate structure, which is one of the robust skeletons for expressing aggregation-induced emission (AIE) properties. From the formation of the boron-centered spiro structure with the ketoiminate ligands, we obtained stable ionic salts with variable anions. Since the ionic salts show T_ms below 100 °C, it was shown that these salts can be classified as an ionic liquid. By using PF₆ anion, the single crystal—which is applicable for X-ray crystallography—was obtained. According to the optical measurements, it was proposed that electronic interaction should occur through the boron center. Moreover, intense emission was observed both in solution and solid. Finally, we demonstrated that the emission color of the PF₆ salt was altered from crystal to amorphous by adding mechanical forces. Based on boron complexation and intrinsic solid-state luminescent characters, we achieved obtainment of emissive ionic materials with environmental responsivity.

Conformation-Dependent Electron Donation of Nido-Carborane Substituents and Its Influence on Phosphorescence of Tris(2,2′-bipyridyl)ruthenium(II) Complex

In this work, we report the synthesis of the nido-carborane-substituted ruthenium complexes and the substituent effects of nido-carboranes on the optical properties. Initially, from the optical measurements, it is shown that deep-red phosphorescence was obtained from the synthesized molecule, and the phosphorescent quantum yields were significantly improved by loading onto a polyethylene glycol film. This result represents that nido-carborane can work as a strong electron donor and should be an effective unit for enhancing the solid-state phosphorescence of ruthenium complexes. Further, it is suggested that the electron-donating properties of the nido-carborane units and subsequently the optical properties can be tuned by controlling the conformation of the nido-carborane units with the steric substituents. We demonstrate in this study the potential of nido-carborane as a building block for constructing optical materials as well as fundamental information regarding electronic interactions with π-conjugated systems.

The Synthesis of Picolinamide-Supported Tetracoordinated Organoboron Complexes with Aggregation-Induced Emission Property

The picolinamide-supported tetracoordinated organoboron complexes containing diaryl boronyl segments have been synthesized for the first time. Aryl trifluoroborates were utilized as the BAr₂ sources to introduce different aryl motifs with diverse functional groups. The optical experiments discovered these five-membered boron-containing complexes were aggregation-induced emission (AIE) active, thus affording a new class of AIE molecules.

Development of Long Wavelength Light-Absorptive Homopolymers Based on Pentaazaphenalene by Regioselective Oxidative Polymerization

We report the synthesis and absorption properties of homopolymers consisting of 1,3,4,6,9b-pentaazaphenalene (5AP). Oxidative polymerization in the Scholl reaction was accomplished, and various lengths of homopolymers can be isolated. It should be noted that we scarcely observed the generation of structural isomers at the connecting points, which is often observed in this type of reaction. Therefore, we were able to evaluate electronic structures of the synthesized homopolymers. In addition, it was observed that absorption bands were obtained in the longer wavelength region than the monomer. The computer calculation suggests that the highest occupied molecular orbital (HOMO) energy levels could be lowered by electronic interaction through spatially-separated HOMOs of 5AP. Moreover, we can evaluate the extension of the conjugated system through the meta-substituted skeleton and distance dependency of the main-chain conjugation.

Bis-Palladium Complex of α-Benzimidazole 9-Pyrrolyl Dipyrromethene: Synthesis, Structure, and Spectral and Catalytic Properties

A new ligand is designed and synthesized in two steps starting from α-formyl 3-pyrrolyl BODIPY. In the first step, the α-formyl 3-pyrrolyl BODIPY was condensed with 1,2-diaminobenzene in toluene at reflux and afforded α-benzimidazole 3-pyrrolyl BODIPY in 16% yield. In the second step, α-benzimidazole 3-pyrrolyl BODIPY was decomplexed upon being treated with Lewis acid AlCl₃ and afforded the desired ligand α-benzimidazole 9-pyrrolyl dipyrromethene. However, the ligand was not very stable and reacted further with PdCl₂ in CH₃CN for 1 h at reflux followed by recrystallization and afforded a novel bis-palladium complex of α-benzimidazole 9-pyrrolyl dipyrromethene in 36% yield. The bis-palladium complex was characterized and studied by high-resolution mass spectrometry, one- and two-dimensional nuclear magnetic resonance, X-ray crystallography, absorption, and density functional theory/time-dependent DFT (DFT/TD-DFT) studies. The X-ray structure revealed that two ligands and two Pd(II) ions were involved in forming a unique complex in which each Pd(II) ion was coordinated to three pyrrole N atoms of the first ligand and the benzimidazole N atom of the second ligand in a distorted square planar geometry. The absorption spectrum of the bis-palladium complex shows ill-defined, broad, and less intense bands in the region of 345-425 nm along with split bands in the higher-wavelength region of 600-630 nm. The bis-palladium complex was nonfluorescent, and the results of DFT/TD-DFT studies were in agreement with the experimental observations. The preliminary studies indicated that the bis-palladium complex can act as an efficient catalyst for coupling different aryl bromides with phenylboronic acid.