Dual Stimuli-Responsive [2]Rotaxanes with Tunable Vibration-Induced Emission and Switchable Circularly Polarized Luminescence

Aiming at the construction of novel stimuli-responsive fluorescent system with precisely tunable emissions, the typical 9,14-diphenyl-9,14-dihydrodibenzo[a, c]phenazine (DPAC) luminogen with attractive vibration-induced emission (VIE) behavior has been introduced into [2]rotaxane as a stopper. Taking advantage of their unique dual stimuli-responsiveness towards solvent and anion, the resultant [2]rotaxanes reveal both tunable VIE and switchable circularly polarized luminescence (CPL). Attributed to the formation of mechanical bonds, DPAC-functionalized [2]rotaxanes display interesting VIE behaviors including white-light emission upon the addition of viscous solvent, as evaluated in detail by femtosecond transient absorption (TA) spectra. In addition, ascribed to the regulation of chirality information transmission through anion-induced motions of chiral wheel, the resolved chiral [2]rotaxanes reveal unique switchable CPL upon the addition of anion, leading to significant increase in the dissymmetry factors (glum ) values with excellent reversibility. Interestingly, upon doping the chiral [2]rotaxanes in stretchable polymer, the blend films reveal remarkable emission change from white light to light blue with significant 6.5-fold increase in glum values up to -0.035 under external tensile stresses. This work provides not only a new design strategy for developing molecular systems with fluorescent tunability but also a novel platform for the construction of smart chiral luminescent materials for practical use.

Modulating the Luminescence, Photosensitizing Properties, and Mitochondria-Targeting Ability of D-π-A-Structured Dihydrodibenzo[a,c]phenazines

Herein, pyridinium and 4-vinylpyridinium groups are introduced into the VIE-active N,N'-disubstituted-dihydrodibenzo[a,c]phenazines (DPAC) framework to afford a series of D-π-A-structured dihydrodibenzo[a,c]phenazines in consideration of the aggregation-benefited performance of the DPAC module and the potential mitochondria-targeting capability of the resultant pyridinium-decorated DPACs (DPAC-PyPF6 and DPAC-D-PyPF6). To modulate the properties and elucidate the structure-property relationship, the corresponding pyridinyl/4-vinylpyridinyl-substituted DPACs, i.e., DPAC-Py and DPAC-D-Py, are designed and studied as controls. It is found that the strong intramolecular charge transfer (ICT) effect enables the effective separation of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of DPAC-PyPF6 and DPAC-D-PyPF6, which is conducive to the generation of ROS. By adjusting the electron-accepting group and the π-bridge, the excitation, absorption, luminescence, photosensitizing properties as well as the mitochondria-targeting ability can be finely tuned. Both DPAC-PyPF6 and DPAC-D-PyPF6 display large Stokes shifts (70-222 nm), solvent-dependent absorptions and emissions, aggregation-induced emission (AIE), red fluorescence in the aggregated state (λem = 600-650 nm), aggregation-promoted photosensitizing ability with the relative singlet-oxygen quantum yields higher than 1.10, and a mitochondria-targeting ability with the Pearson coefficients larger than 0.85. DPAC-D-PyPF6 shows absorption maximum at a longer wavelength, slightly redder fluorescence and better photosensitivity as compared to DPAC-PyPF6, which consequently leads to the higher photocytotoxicity under the irradiation of white light as a result of the larger π-conjugation.

Multicolor emission based on a N, N'-Disubstituted dihydrodibenzo [a, c] phenazine crown ether macrocycle

Dynamic fluorophore 9,14-diphenyl-9,14-dihydrodibenzo[a,c]phenazine (DPAC) affords a new platform to produce diverse emission outputs. In this paper, a novel DPAC-containing crown ether macrocycle D-6 is synthesized and characterized. Host-guest interactions of D-6 with different ammonium guests produced a variety of fluorescence with hypsochromic shifts up to 130 nm, which are found to be affected by choice of solvent or guest and host/guest stoichiometry. Formation of supramolecular complexes were confirmed by UV-vis titration, ¹H NMR and HRMS spectroscopy.

A Lipidated Peptide with Mitochondrial Membrane Localization in Human A549 Lung Cells: From Enhanced Cell-Penetrating Properties to Biological Activity Mechanism

Here, a lipidated peptide Pal-pHK-pKV with self-assembly properties and the ability to provoke the disruption of the mitochondrial voltage-dependent anion channel-1 protein (VDAC1)-hexokinase-II (HK-II) complex is reported. The effects of the peptide pHK (N-terminal 15-amino acid fragment of HK-II that specifically binds VDAC1) are compared to those of a designed biomimetic amphiphilic pHK-pKV conjugate (pHK coupled with a cell-penetrating peptide pKV) and Pal-pHK-pKV (a lipidated conjugate modified with a hydrophobic palmitic (Pal) alkyl chain). The Pal-pHK-pKV exhibits a stronger interaction with the membrane as compared to pHK-pKV, which is demonstrated by the Langmuir-Blodgett technique and two-photon excitation microscopy. The amphiphilic peptide derivatives are cytotoxic to the A549 cells, but Pal-pHK-pKV is more cytotoxic. The inhibitory effects of the pHK derivatives on the A549 cells growth are investigated through induced apoptosis pathway, depolarized mitochondrial membrane potential, inhibited glycolysis, and activated caspase. The results of the immunofluorescence evidence the specific mitochondrial targeting by those derivatives.

Visually Monitoring the Compactness of Polymer Matrixes Coded by Disparate Luminescence

The intrinsic property disclosure of polymer systems by visual monitoring of photoluminescence behaviors is of great value in fundamental interest and promising applications. Three novel polymer films were obtained by simply doping methyl 9,14-diphenyl-9,14-dihydrodibenzo[a,c]phenazine-11-carboxylate (DPC) with three polymer materials. The photoluminescence behaviors of these films represented diverse fluorescence emissions from light orange to blue, especially room-temperature phosphorescence (RTP) emissions with ultralong lifetime, attributing to various configurations of DPC molecules provided by distinct microscopic environments in three polymer systems. The rigidity and regularity of polymer systems would be visually reflexed by luminescence regulation and temperature responses. In addition, irregular distribution of distinct polymer systems could be specifically monitored by both fluorescence and phosphorescence behaviors when doping different polymer materials into one blend film.

A Vibration-Induced-Emission-Based Fluorescent Chemosensor for the Selective and Visual Recognition of Glucose

The development of chemosensors to detect analytes in biologically relevant solutions is a challenging task. We report the synthesis of a fluorescent receptor that combines vibration-induced emission (VIE) and dynamic covalent chemistry for the detection of glucose in aqueous media. We show that the bis-2-(N-methylaminomethyl)phenylboronic acid-decorated N,N'-diphenyl-dihydrodibenzo[a,c]phenazine (DPAC) receptor 1 can detect glucose and discriminate between closely related monosaccharides including those commonly found in blood. Preliminary studies suggest monosaccharides bind to the DPAC-receptor with a 1:1 stoichiometry to produce pseudomacrocyclic complexes, which in turn leads to distinct optical changes in the fluorescent emission of the receptor for each host. Moreover, the complexation-induced change in emission can be detected visually and quantified in a ratiometric way. Our results highlight the potential of VIE-type receptors for the quantitative determination of saccharides in biological samples.

Real-Time Visual Monitoring of Kinetically Controlled Self-Assembly

The construction of artificial structures through hierarchical self-assembly based on noncovalent interactions, as well as monitoring during the self-assembly process, are important aspects of dynamic supramolecular chemistry. Herein we describe the complex dynamics of chiral N,N'-diphenyl dihydrodibenzo[a,c]phenazine derivatives (S)/(R)-DPAC, whose different assemblies were found to have distinct optical and morphological characteristics. With ratiometric fluorescence originating from vibration-induced emission (VIE), the self-assembly process from kinetic traps to the thermodynamic equilibrium state could be monitored in real time by optical spectrometry. During the morphology transformation from particles to nanobricks, strong circularly polarized luminescence was induced with g_lum =1.6×10^-2 . The excited-state characteristics of the self-assemblies enabled investigation of the relationship between molecular aggregation and conformational change, thus allowing effective monitoring of the sophisticated supramolecular self-assembly process.

Ratiometric Indicator Based on Vibration-Induced Emission for in Situ and Real-Time Monitoring of Gelation Processes

Monitoring specific processes such as gelation in a ratiometric and visual manner is of scientific value and has practical implications but remains challenging. Herein, an innovative fluorescent low-molecular-weight gelator (DPAC-CHOL) capable of revealing and self-revealing the gelation processes in situ and in real time via the ratiometric fluorescence change from orange-red to blue has been developed. By virtue of its vibration-induced emission attribute, the gelation point, critical gelation concentration, and the internal stiffness of the gel networks of DPAC-CHOL and other gelation systems could be facilely evaluated in a ratiometric and naked-eye-observable fashion. Noteworthily, the DPAC-CHOL-doped gelation system Ph-CHOL can quantitatively identify the environmental temperature in a daily-concerned range (i.e., 20-55 °C). This work not only provides a versatile advanced material but also opens up a new avenue for the investigation of gelation systems.

Phenazine-Based Ratiometric Hg2+ Probes with Well-Resolved Dual Emissions: A New Sensing Mechanism by Vibration-Induced Emission (VIE)

Phenazines exhibit intriguing vibration-induced emission (VIE) owing to the fast intrinsic vibration of benzo[a,c]phenazine moiety. For the first time, a phenazine-based ratiometric fluorescent probe DBPST is developed for recognizing Hg²⁺ via restriction of VIE. Upon binding with Hg²⁺ , DBPST demonstrates two well-resolved emission peaks (over 130 nm) with a wide tuning color and affords a large signal-to-background ratio.