Synthesis of aza-BODIPY dyes bearing the naphthyl groups at 1,7-positions and application for singlet oxygen generation

Near-IR-Absorbing Bis-Donor Functionalized Aza-BODIPY Derivatives: Synthesis and Photophysical Study by Using Transient Optical Spectroscopy

A series of near-IR absorbing 2,6-diarylated BF2-chelated aza-boron-dipyrromethenes (aza-BDPs) derivatives bearing different electron donors (benzene, naphthalene, phenanthrene, phenothiazine and carbazole) were designed and synthesized. The effect of different electron donor substitutions on the photophysical properties was studied by steady-state UV-vis absorption and fluorescence spectra, electrochemical, time-resolved nanosecond transient absorption (ns-TA) spectroscopy and theoretical computations. The UV-vis absorption spectra of AzaBDP-PTZ and AzaBDP-CAR (λabs=710 nm in toluene) showed a bathochromic absorption profile compared with the reference AzaBDP-Ph (λabs=685 nm in toluene), indicating the non-negligible electronic interaction at the ground state between donor and acceptor moieties. Moreover, the fluorescence is almost completely quenched for AzaBDP-PTZ/AzaBDP-CAR (fluorescence quantum yield, ΦF=0.2-0.7 % in toluene) as compared with the AzaBDP-Ph (ΦF=27 % in toluene). However, the apparent intersystem crossing ability of these compounds is poor, based on the singlet oxygen quantum yield (ΦΔ=0.3-1.5 %). The ns-TA spectral study showed typical Bodipy localized triplet state transient features, short-lived excited triplet state for AzaBDP-Ph (τT=53.2 μs) versus significantly long-lived triplet state for AzaBDP-CAR (τT=114 μs) was observed under deaerated experimental conditions. These triplet state lifetimes are much longer than that obtained with diiodoAzaBDP (intramolecular heavy atom effect, τT=1.5~7.2 μs). These information are useful for molecular structure design of triplet photosensitizers, for which longer triplet state lifetimes are usually desired. Theoretical computations displayed that the triplet state is mainly localized on the AzaBDP core, moreover, it was found that the HOMO/LUMO energy gap decreased after introducing donor moieties to the skeleton as compared with the reference.

Monoarsine-protected icosahedral cluster [Au13(AsPh3)8Cl4]+: comparative studies on ligand effect and surface reactivity with its stibine analogue

Ligand shells of gold nanoclusters play important roles in regulating their molecular and electronic structures. However, the similar but distinct impacts of the homologous analogues of the protecting ligands remain elusive. The C_2v symmetric monoarsine-protected cluster [Au₁₃(AsPh₃)₈Cl₄]⁺ (Au₁₃As₈) was facilely prepared by direct reduction of (Ph₃As)AuCl with NaBH₄. This cluster is isostructural with its previously reported stibine analogue [Au₁₃(SbPh₃)₈Cl₄]⁺ (Au₁₃Sb₈), enabling a comparative study between them. Au₁₃As₈ exhibits a blue-shifted electronic absorption band, and this is probably related to the stronger π-back donation interactions between the Au₁₃ core and AsPh₃ ligands, which destabilize its superatomic 1P and 1D orbitals. In comparison to the thermodynamically less stable Au₁₃Sb₈, Au₁₃As₈ achieves a better trade-off between catalytic stability and activity, as demonstrated by its excellent catalytic performance towards the aldehyde-alkyne-amine (A³) coupling reaction. Moreover, the ligand exchange reactions between Au₁₃As₈ with phosphines, as exemplified by PPh₃ and Ph₂P(CH₂)₂PPh₂, suggest that Au₁₃As₈ may be a good precursor cluster for further cluster preparation through the "cluster-to-cluster" route.

Near-Infrared Dyes: Towards Broad-Spectrum Antivirals

Broad antiviral activity in vitro is known for many organic photosensitizers generating reactive oxygen species under irradiation with visible light. Low tissue penetration of visible light prevents further development of antiviral therapeutics based on these compounds. One possible solution to this problem is the development of photosensitizers with near-infrared absorption (NIR dyes). These compounds found diverse applications in the photodynamic therapy of tumors and bacterial infections, but they are scarcely mentioned as antivirals. In this account, we aimed to evaluate the therapeutic prospects of various NIR-absorbing and singlet oxygen-generating chromophores for the development of broad-spectrum photosensitizing antivirals.

Synthesis of trifluoromethylated aza-BODIPYs as fluorescence-19F MRI dual imaging and photodynamic agents

Dual-imaging agents with highly sensitive fluorescence (FL) imaging and highly selective fluorine-19 magnetic resonance imaging (¹⁹F MRI) are valuable for biomedical research. At the same time, photosensitizers with a high reactive oxygen species (ROS) generating capability are crucial for photodynamic therapy (PDT) of cancer. Herein, a series of tetra-trifluoromethylated aza-boron dipyrromethenes (aza-BODIPYs) were conveniently synthesized from readily available building blocks and their physicochemical properties, including ultraviolet-visible (UV-Vis) absorption, FL emission, photothermal efficacy, ROS generating efficacy, and ¹⁹F MRI sensitivity, were systematically investigated. An aza-BODIPY with 12 symmetrical fluorines was identified as a potent FL-¹⁹F MRI dual-imaging traceable photodynamic agent. It was found that the selective introduction of trifluoromethyl (CF₃) groups into aza-BODIPYs may considerably improve their UV absorption, FL emission, photothermal efficacy, and ROS generating properties, which lays the foundation for the rational design of trifluoromethylated aza-BODIPYs in biomedical applications.

Two-photon absorption and triplet excited state quenching of near-IR region aza-BODIPY photosensitizers via a triphenylamine moiety despite heavy bromine atoms

Aza-BODIPY compounds with methoxy groups at -3 and -5 positons and triphenylamine moieties at -1, -7 positions with and without heavy bromine atoms at -2, -6 positions have been designed and synthesized.

An amphiphilic B,O-chelated aza-BODIPY dye: synthesis, pH-sensitivity, and aggregation behaviour in a H2O/DMSO mixed solvent

A novel amphiphilic B,O-chelated azadipyrromethene (aza-BODIPY) dye, containing hydrophobic dodecyloxy groups and hydrophilic tetraethylene glycol (TEG) chains, was synthesized and characterized by NMR, HRMS, Vis/NIR absorption and fluorescence spectroscopy. The B,O-chelated dye 1 exhibited largely bathochromically shifted NIR absorption and fluorescence spectra in comparison with common BF₂-chelated aza-BODIPY dyes. Upon gradual addition of trifluoroacetic acid (TFA) to the dye 1 solution, obvious spectral changes were observed in Vis/NIR absorption and fluorescence spectroscopy measurements. Meanwhile, the colour change of the dye 1 solution from pink to blue was noticeable by the naked eye, indicating the pH-sensitivity of dye 1. The pH-sensitivity of dye 1 under acidic conditions could be ascribed to the formation of dye species 2·H⁺. Furthermore, owing to the amphiphilic feature of dye 1, it self-assembled into J-type aggregates in a mixed solvent of water/DMSO (2/8, v/v). Temperature-dependent Vis/NIR spectroscopic studies revealed a cooperative aggregation process of dye 1 and a nanowire-like morphology of the nanoaggregates was observed by AFM.