Tunable Self-Assembly and Aggregation-Induced Emission Characteristics of Triarylboron-Decorated Naphthalimides

Novel Iminocoumarin-substituted Tetraphenylethylene-based Near-infrared Fluorescent Probe for Ratiometric Detection of F- and H2S

An iminocoumarin and tetraphenylethylene compound that exhibits aggregation-induced emission (AIE) and a significant Stokes shift (Δλ = 135 nm) in THF was created via the Knoevenagel condensation method. TPICBT could also be used as a ratiometric near-infrared fluorescent probe for the naked color identification of F- and H2S. It showed a large red shift (˃ 90 nm), good selectivity, and anti-interference. Test strip detection and cell imaging had both been accomplished using the probe. In addition, the probe could conveniently detect H2S produced during food spoilage without laboratory instruments.

Polymorphism Dependent Cytotoxicity, Cellular Uptake, and Live Cell Imaging Studies on Napthalimide-Vinyl-Phenothiazine Conjugate

Polymorphism-dependent cytotoxicity and cellular uptake of drug molecules have been studied for the past two decades. However, the visualization of polymorph-dependent cellular uptake and cytotoxicity using microscopy imaging techniques has not yet been reported. The luminescent polymorph is an ideal candidate to validate the above hypothesis. Herein, we report the polymorph-dependent cellular uptake, cytotoxicity, and bio-imaging functions of polymorphs 1Y and 1R of a naphthalimide-phenothiazine dyad. These polymorphs show different luminescence colors in the solid state and exhibit aggregation-induced enhanced emission (AIEE) in the DMSO-Water mixture. Bioimaging, cytotoxicity assay, and fluorescence-activated cell sorting (FACS) studies revealed that these polymorphs show different levels of cytotoxicity, cellular uptake, localization, and imaging potential. Detailed photophysical, morphological, and biological studies revealed that the difference in molecular conformation in these polymorphs enables them to form aggregates of different sizes and morphology, which leads to the differential uptake of these into the cells and consequently shows different cytotoxicity and imaging potentials.

Synthesis of triarylborane-centered N-heterocyclic carbene cages with tunable photophysical properties

Triarylborane-based discrete metal-carbene supramolecular cages [M₃(1)₂](PF₆)₃ (M = Ag, Au) were synthesized and characterized. The new hexacarbene assemblies show a significant solvatochromic effect in solvents of different polarity. Furthermore, the reversible fluoride binding property of [Au₃(1)₂](PF₆)₃ was investigated by UV-vis absorption and fluorescence titrations. This work holds promise for future developments in the area of highly emissive and stimulus-responsive NHC-metal assemblies.

Effects of functional groups and side chains on assembly of "X"-shaped new aggregation-induced emission molecules

The self-assembly properties of aggregation-induced emission molecules play important roles in electroluminescence devices and fluorescence sensors because noncovalent interactions in self-assembly structures would accelerate the excitation energy consumption. However, there are only few studies to explore their self-assembly properties on the interface and there is still a great need for further understanding self-assembled mechanisms from the viewpoint of molecular design. Here, we presented three X-shaped aggregation-induced emission molecules X1, X2 and X3, which decorated with different functional groups and alkyl side chains. The self-assembly structures were revealed by scanning tunneling microscopy technique in combination with density functional theory. Results showed that X-shaped molecules self-assembled into different structures, depending on their molecular structure, especially the functional groups. Furthermore, self-assembly structures could be regulated by adjusting solution concentration. In more detail, parallel with gradually increasing solution concentration, the molecules approached closer and molecule-molecule interactions were enhanced, finally resulting in new nanostructures. The self-assembly properties of three X-shaped aggregation-induced emission molecules on the liquid/solid interface would give a guidance for further exploring the aggregation state in three-dimensional space. Meanwhile, the two-dimensional nanostructures might show special properties, which could be used in fabricating next generation functional films.

Bipolar 1,8-naphthalimides showing high electron mobility and red AIE-active TADF for OLED applications

Aiming to design bipolar organic semiconductors with high electron mobility and efficient red thermally activated delayed fluorescence (TADF), three donor-acceptor compounds were designed and synthesized selecting 1,8-naphthalimide as an acceptor and phenoxazine, 3,7-di-tert-butylphenothiazine or 2,7-di-tert-butyldimethyl-9,10-dihydroacridine as donor moieties. Aggregation induced emission enhancement was detected for the compounds causing efficient TADF in the solid-state. Photoluminescence quantum yields up to 77% were observed for the films of the compounds doped in a host. The compounds exhibited small singlet-triplet splitting (0.03-0.05 eV), and high reverse intersystem crossing rates of 2.08 × 10⁵-1.13 × 10⁶ s^-1. The compounds were characterized by satisfactory hole and electron-injecting properties with ionization potentials of 5.72-5.83 eV and electron affinities of 2.79-2.91 eV. Bipolar charge transport was revealed by time of flight measurements. Electron transport with low dispersity and mobilities exceeding 2 × 10^-3 cm² V^-1 s^-1 was observed at an electric field of 4.6 × 10⁵ V cm^-1. The compounds were used as emitters in red electroluminescent devices, which showed maximum external quantum efficiencies up to 8.2%. Utilization of host-guest systems as light-emitting materials with hosts preferably transporting holes and TADF guests which preferably transport electrons allowed maximum efficiencies to be achieved at a practical brightness of 700-2200 cd m^-2. DFT calculations of the geometry, electronic structure, absorption and photoluminescence spectra of all compounds were carried out to prove the conclusions drawn from the experiment. The results of the calculations clearly show that the first excited state for all compounds is the intramolecular charge transfer state. Quantitative analysis of the separation degree of electronic density during excitation allows the observed dependence of the blue shift value in the absorption and emission spectra on the increasing polarity of the solvent to be explained.

Fluorescent small molecules with alternating triarylamine-substituted selenophenothiophene and triarylborane: synthesis, photophysical properties and anion sensing studies

Two novel D-π-A fluorophores based on selenopheno[3,2-b]thiophene, possessing triphenylamine and 4,4'-dimethoxytriphenylamine units as donors and dimesitylborane as an acceptor, linked through a π-conjugated thiophene spacer (BTPAST and BOMeTPAST, respectively) were synthesized. Their photophysical properties were investigated in both solution and the state of aggregation and compared to those of their corresponding donor parts, having no dimesitylborane units (TPAST and OMeTPAST). All the compounds displayed large Stokes shifts between 100 and 140 nm with positive solvatochromism in solvents having different polarities. While BTPAST displayed both aggregation induced emission (AIE) and twisted intramolecular charge transfer (TICT) characteristics, the others preponderated with TICT effects. The sensing abilities of BTPAST and BOMeTPAST towards different anions were studied. Both exhibited chromogenic and fluorogenic responses to small anions such as fluoride and cyanide, for which the detection limits were found to be 0.12 and 2.43 ppm with BTPAST and 0.59 and 0.92 ppm with BOMeTPAST, respectively. These results provide guidance for the development of novel fused selenophenothiophene sensors in the field of anion sensing.

1D alignment of Co(II) metalated porphyrin-napthalimide based self-assembled nanowires for photocatalytic hydrogen evolution

The splitting of water into hydrogen and oxygen under visible light is an emerging phenomenon in green energy technology. Nevertheless, selecting an appropriate photocatalyst is rather significant to enhance hydrogen production on a large scale. In this context, organic photocatalysts have received considerable attention owing to their larger surface area, control in diffusion adsorption, nanostructures and electronic properties. Herein, we have developed five either free base or transition metalated porphyrin-napthalimide based donor-acceptor systems (PN1-PN5) and studied their morphology, electronic properties and catalytic behaviour. Detailed studies suggest that the Co(II) substituent D-A system (PN2) displayed a well-aligned one-dimensional (1D) nanowire with high electrical conductivity promoting remarkable photocatalytic hydrogen production rate (18 mM g^-1 h^-1) when compared to that of porphyrin-based derivatives reported until now. Thus, these results propose to investigate diverse metalated π-conjugated materials as photocatalysts for hydrogen production.

Synthesis of Highly Functionalizable Symmetrically and Unsymmetrically Substituted Triarylboranes from Bench-Stable Boron Precursors

A novel and convenient methodology for the one-pot synthesis of sterically congested triarylboranes by using bench-stable aryltrifluoroborates as the boron source is reported. This procedure gives systematic access to symmetrically and unsymmetrically substituted triarylboranes of the types BAr2 Ar' and BArAr'Ar'', respectively. Three unsymmetrically substituted triarylboranes as well as their iridium-catalyzed C-H borylation products are reported. These borylated triarylboranes contain one to three positions that can subsequently be orthogonally functionalized in follow-up reactions, such as Suzuki-Miyaura cross-couplings or Sonogashira couplings.

Turn-on fluorescent naphthalimide-benzothiazole probe for cyanide detection and its two-mode aggregation-induced emission behavior

Naphthalimide-benzothiazole conjugate (NBTZ) linked by cinnamonitrile was designed, synthesized, and fully characterized by NMR (¹H, ¹³C, DEPT, HSQC) and high-resolution mass spectrometry. NBTZ exhibited unique turn-on fluorescence in the presence of CN^- with relatively high selectivity compared to other anions such as SCN^-, HSO₄^-, ClO₄^-, NO₃^-, Cl^-, Br^-, I^-, and PO₄^-3 in tetrahydrofuran (THF). The detection limit for CN^- was found to be 3.35 × 10^-8 M in THF. The sensing mechanism was analyzed through ¹H, ¹³C, DEPT, and mass spectroscopy. NBTZ also showed two-mode aggregation-induced emission (AIE) in THF-H₂O mixtures. In a 30:70 THF-H₂O (v/v) mixture, the maximum AIE was observed at 430 nm (blue) because of the rotation of the CC bond between the naphthalimide ring and the phenyl ring was restricted. In 10:90 THF-H₂O (v/v), a new red-shifted AIE appeared at 490 nm (cyan), due to the extended π-conjugation induced by restriction of rotation of the CC bond between the benzothiazole and naphthalimide rings.

Aggregation-induced emission enhancement (AIEE)-active tetraphenylethene (TPE)-based chemosensor for CN. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2021;245:118928. [PMID: 32950857 DOI: 10.1016/j.saa.2020.118928]

An aggregation-induced emission enhancement (AIEE)-active fluorescent sensor has been successfully designed and synthesized, combining the AIE effect of tetraphenylethylene (TPE) with the cyanide acceptor of phenanthro[9,10-d]imidazole. The sensor exhibits not only the property of AIEE in DCM/n-hexane or THF/H₂O, but also the phenomenon of mechanofluorochromic (MFC). It displays large Stokes shift (107 nm) due to the intramolecular charge transfer (ICT) process. The cation of CN^- boosts the ICT process to make the greater Stokes shift (184 nm) with the fluorescent color vary from blue-green to sodium-yellow and visually turning from light yellow to dark yellow in the naked eyes. The results of Job's plot, ESI-MS and the DFT calculations provide the stoichiometric ratio and electronic properties of the sensor. Furthermore, the sensor could be applied to qualitative and quantitative detection of CN^- on test paper strips.

Delayed Fluorescence, Room Temperature Phosphorescence, and Mechanofluorochromic Naphthalimides: Differential Imaging of Normoxia and Hypoxia Live Cancer Cells

We study the effect of molecular conformation on the electronic coupling between the donor amines and acceptor 1,8-naphthalimide (NPI) in a series of D-A systems 1-4 (A = NPI; D = phenothiazine, phenoxazine, carbazole, diphenylamine, respectively, for 1, 2, 3, and 4). Weakly coupled systems show dual emission in the solution state, while strongly coupled systems show single emission bands. The energy of transitions and photoluminescence (PL) quantum yield are sensitive to the molecular conformation and donor strength. These compounds show delayed emission in the solutions and aggregated state and phosphorescence in the solid state. Compounds 3 and 4 with weak donors exhibit intermolecular slipped π···π interactions in the solid state and consequently exhibit dual (intra- and inter-) phosphorescence at low temperature. Steady state and time-resolved PL studies at variable temperature together with computational and crystal structure analysis were used to rationalize the optical properties of these compounds. The delayed emission of these compounds is sensitive to molecular oxygen; accordingly, these molecules are utilized for differential imaging of normoxia and hypoxia cancer cells.

Azine based AIEgens with multi-stimuli response towards picric acid

Selective detection of picric acid using AIEgens via fluorescence enhancement and quenching in the monomer and aggregated from respectively.

A Strongly Fluorescent Molecular Material Responsive to Physical/Chemical Stimuli and their Coupled Impact

Molecular materials with weak but extended and pliable supramolecular interactions are versatile candidates for eliciting stimuli-sensitive optical responses. A novel diaminodicyanoquinodimethane (DADQ) molecule, 7,7-bis(2-(2-pyridyl)ethylamino)-8,8-dicyanoquinodimethane (BPEDQ), has been synthesized and structurally characterized; it exhibits enhanced fluorescence emission in the aggregated and solid states, characteristic of DADQs. The pyridine moieties in the molecule, in addition to the amino and cyano groups of the strongly dipolar fluorophore moiety, induce extensive H-bonding interactions which can impart structural integrity to the solid material; this enables reversible crystalline-amorphous transformations triggered by mechanical grinding and solvent fuming. The concomitant fluorescence color and intensity switching are prominent and reversible. Protonation-deprotonation events induced by acidic and basic vapors also produce stark fluorescence response variations; the chemical stimuli also lead to amorphization of the solid. The full cycle of chemical and physical stimuli, and the consequence of their individual and coupled impact on the fluorescence emission, are illustrated using a BPEDQ-doped polymer thin film.

Borylated perylenediimide: self-assembly, photophysics and sensing application

A red emissive perylenediimide-triarylboron conjugate (PDI-TAB) with interesting 1D self-assembled nanowires, concentration dependent emission colors and potential fluoride ion sensing is reported.