Wei Chen

Herein, we introduce the cyclic 8π‐electron (C8π) molecule N,N′‐diaryl‐dihydrodibenzo[a,c]phenazine (DPAC) as a dual‐functional donor to establish a series of new donor–linker–acceptor (D–L–A) dyads DLA1–DLA5. The excited‐state bent‐to‐planar dynamics of DPAC regulate the energy gap of the donor, while the acceptors A1–A5 are endowed with different energy gaps and HOMO/LUMO levels. As a result, the rate and efficiency of the excited‐state electron transfer vs. energy transfer can be finely harnessed, which is verified via steady‐state spectroscopy and time‐resolved emission measurements. This comprehensive approach demonstrates, for the first time, the manifold of excited‐state properties governed by bifunctional donor‐based D–L–A dyads, including bent‐to‐planar, photoinduced electron transfer (PET) from excited donor to acceptor (oxidative‐PET), fluorescence resonance energy transfer (FRET), bent‐to‐planar followed by electron transfer (PFET), and PET from donor to excited acceptor (reductive‐PET).

Herein, we introduce the cyclic 8π‐electron (C8π) molecule N,N′‐diaryl‐dihydrodibenzo[a,c]phenazine (DPAC) as a dual‐functional donor to establish a series of new donor–linker–acceptor (D–L–A) dyads DLA1–DLA5. The excited‐state bent‐to‐planar dynamics of DPAC regulate the energy gap of the donor, while the acceptors A1–A5 are endowed with different energy gaps and HOMO/LUMO levels. As a result, the rate and efficiency of the excited‐state electron transfer vs. energy transfer can be finely harnessed, which is verified via steady‐state spectroscopy and time‐resolved emission measurements. This comprehensive approach demonstrates, for the first time, the manifold of excited‐state properties governed by bifunctional donor‐based D–L–A dyads, including bent‐to‐planar, photoinduced electron transfer (PET) from excited donor to acceptor (oxidative‐PET), fluorescence resonance energy transfer (FRET), bent‐to‐planar followed by electron transfer (PFET), and PET from donor to excited acceptor (reductive‐PET).

The development of colour-tunable white-light-emitting systems is significant for artificial smart materials. Recently, a set of conformational dependent fluorophores N,N′-diaryl-dihydrodibenzo[a,c]phenazines (DPACs) have been developed with unique photoluminescence mechanism vibration-induced emission (VIE). DPACs can emit intrinsical blue emission at bent excited state and abnormal orange-red emission at planar exctied state, which is due to the varied π-conjugation via excited state configuration transformation along the N-N′ axis from bent to planar form. Herein, a novel VIE-active compound DPAC-[B15C5]2 is designed and synthesized with two wings of benzo-15-crown-5. The excited state vibration of the DPAC moiety can be modulated by tuning the supramolecular assembly and disassembly via chelation competition of K+ between 15-crown-5 and 18-crown-6, and hence a wide-colour-tuning emission is achevied from blue to orange-red including white. Dynamic light scattering (DLS) and transmission electron microscope (TEM) experiments were conducted to exhibit the supramolecular assembling process. Additionally, the moiture detection in organic solvents is realized since the water could dissociate the supramolecular assembly.

We report here the fluorescent sensing of both aromatic and linear saturated dicarboxylate anions (DC^2–) (as their tetrabutylammonium salts) with different lengths and shapes in acetonitrile using a single fluorescent probe, i.e., the bis-calix[4]pyrrole-appended 9,14-diphenyl-9,14-dihydrodibenzo[a,c]phenazine (DPAC-bisC4P) incorporating a vibration-induced emission (VIE) phenazine core. Fluorescence titration studies revealed that treating DPAC-bisC4P with dicarboxylate guests capable of forming pseudo-macrocyclic host–guest complexes via multiple hydrogen bonding interactions between the dicarboxylates and calix[4]pyrrole moieties, led to a blue-shift in the emission of the phenazine core. The binding-based fluorescence tuning features of DPAC-bisC4P allows the underlying binding events and inferred structural changes to be monitored in the form of different chromaticity outputs. The analyte-induced differences in the fluorescence response to DC^2– cover a wide range within the chromaticity diagram and can be visualized readily. The present system thus functions as a rudimentary dicarboxylate anion sensor. It highlights the potential benefits associated with combining a tunable VIE core with non-covalent binding interactions and thus sets the stage for the development of new fluorescent chemosensors where a single chemical entity responds to different analytes with a high level of tunability.

Reported here is a two-layer gel construct that permits the on-site detection of the chloride anion by means of a hand-held UV-vis lamp and a smart phone “app”. To prepare this system, eight fluorescent polymeric gels G1–G8 were synthesized. Gels G1–G4 containing C4P/imidazolium-F⁻ anion recognition motifs were used to construct a fluorescent pattern (Code A) that may be read out by a smart phone as a 3D color code (Info A). Gels G5–G8, which are based on C4P/imidazolium-Br⁻ anion interactions, were used to construct an array (Code B) that may be read as Info B. Code B was then adhered to the surface of Code A to produce an adhered double layer code system stabilized by interfacial C4P/imidazolium-Br⁻ anion interactions. Readout of the top layer (Code B) could be achieved without interference from Code A. Treatment with a Cl⁻ anion source was found to delaminate the top layer and leave intact the more robust bottom layer, allowing the bottom layer (Code A) to be read out. The disparate information content associated with Codes A and B thus permits the on-site recognition of Cl⁻. The present sensing strategy does not rely on elaborate instrumentation and could provide a new application for elaborated soft materials.

To address the challenge of removing unwanted anions from aqueous media under extraction‐free conditions we have prepared a thermoresponsive amphiphilic polymer with pendent calix[4]pyrrole (C4P) receptors. Because of its amphipathicity, this polymer self‐assembles into micelles in water. These micelles contain the C4P receptors buried in a hydrophobic core. This allows uptake of various cesium anions into the micelles. Due to the thermal responsiveness of the hydrophilic block chain, the anion‐bearing micelles precipitate in water upon heating. Simple filtration allows their removal from the aqueous environment, thus allowing for effective water purification. Treating the anion‐trapped micelles with acidic aqueous solution leads to the competition‐induced release of the bound anion and thus recycling the polymeric material.

Achieving ratiometric thermometry with a single organic luminophore is a tempting but challenging task. Herein, three dihydrophenazine‐based ratiometric thermometers, namely DPC, DPSi‐1, and DPSi‐2, are facilely developed via the novel vibration‐induced emission (VIE) strategy. By elaborately introducing alkyl/siloxane chains to the dihydrophenazine core, these fluorophores exhibit as powder with low melting point or nonvolatile liquids, which emit temperature‐sensitive dual emissions: predominantly blue fluorescence (FL) at low temperature and chiefly orange‐red FL at high temperature. According to the VIE mechanism, high temperature activates the intramolecular motions, thus facilitates the excited‐state configuration transformation of the phenazine moiety from bent to planar, as confirmed by the molecular dynamics calculation. The invisible temperature information over a broad range from 5 to 135 °C can be vividly revealed by these VIE‐based ratiometric thermometers, with a high sensitivity (3.40% per °C), a wide linear response region (50–135 °C) and good reversibility, in a solvent‐free and naked‐eye observable manner. Very importantly, these thermometers can be coated onto any object surface for simple and fast large‐area temperature detection, demonstrating their superior practicability compared with other luminescent thermometers. The ratiometric thermometry scheme proposed here may offer new insights into developing thermometers for various applications.

Utilizing supramolecular assembling system to achieve tunable photoluminescence emission has become an important method for the development of light‐emitting materials, which could bring out intriguing photophysical properties out of the luminophores themselves without a demanding design and tedious chemical synthesis. In the last few years, vibration‐induced emission (VIE) molecules, with dual photoluminescence emissions and large Stokes shift, have shown their talent in generating tunable fluorescence and potential in fabricating novel light‐emitting materials. However, little attention has been devoted to explore the attractive properties of VIE molecules in supramolecular self‐assembling systems up to now. Herein, the first example of a supramolecular assembling system composed of a water‐soluble VIE molecule N,N′‐diphenyl‐dihydrodibenzo[a,c]phenazines derivative (DPAC‐AB) and bis‐p‐sulfonatocalix[4]arene (BSC4) is introduced. Based on noncovalent interactions including hydrophobic interaction and host–guest interaction between DPAC‐AB and BSC4, tunable fluorescence emissions from orange‐red to white (Commission Internationale de L'éclairage (CIE) coordinates (0.32, 0.37)) to blue are achieved by simple addition of different amounts of BSC4 to the solution of DPAC‐AB. Additionally, a competitive guest acetylcholine is utilized to recover the nearly orange‐red fluorescence emission. This strategy to efficiently control the emission of VIE molecules through supramolecular assembling based on reversible noncovalent interactions opens new avenues in developing tunable light‐emitting materials.

Two novel ratiometric fluorometric probes 6 a and 6 b have been designed and synthesized for the detection of Hg²⁺ and Ag⁺, respectively. Each of these probes is comprised of a 9,14‐diphenyl‐9,14‐dihydrodibenzo[a,c]phenazine (DPAC) skeleton, a tetraphenylethylene (TPE) unit, and two thymine/adenine groups. In this proof‐of‐concept work, the DPAC unit featuring vibration‐induced emission (VIE) characteristics serves as a dual‐emission chromogen, whereas the TPE moiety, which is noted for its aggregation‐induced emission (AIE) properties, functions mainly as a signal amplifier. The coordination between the thymine/adenine groups and Hg²⁺/Ag⁺ leads to the formation of aggregates, which restricts the intramolecular vibrations of DPAC and the intramolecular rotations of TPE, activating the AIE effect of TPE and resulting in the bent form of DPAC. Accordingly, the overall fluorescence changed from moderate orange‐red (I_orange‐red) to intense blue light (I_blue) passing through the white‐light region, concurrently with an enhancement of fluorescence at 475 nm and a dramatic increase in the ratio of I_blue/I_orange‐red. Furthermore, the superb sensitivity of 6 a/6 b towards Hg²⁺/Ag⁺ has been demonstrated by the detection limit, which is as low as 6.1 nm and 0.1 μm, respectively. Both of these values are below the maximum concentration in drinking water permitted by the U.S. Environmental Protection Agency, demonstrating their great potential to be applied for real‐world metal‐ion sensing.

For deeper understanding of the coupling of electronic processes with conformational motions, we exploit a tailored strategy to harness the excited-state planarization of N,N′-disubstituted dihydrodibenzo[a,c]phenazines by halting the structural evolution via a macrocyclization process. In this new approach, 9,14-diphenyl-9,14-dihydrodibenzo[a,c]phenazine (DPAC) is used as a prototype, in which the para sites of 9,14-diphenyl are systematically enclosed by a dialkoxybenzene-alkyl-ester or -ether linkage with different chain lengths, imposing various degrees of constraint to impede the structural deformation. Accordingly, a series of DPAC-n (n = 1–8) derivatives were synthesized, in which n correlates with the alkyl length, such that the strength of the spatial constraint decreases as n increases. The structures of DPAC-1, DPAC-3, DPAC-4, and DPAC-8 were identified by the X-ray crystal analysis. As a result, despite nearly identical absorption spectra (onset ∼400 nm) for DPAC-1–8, drastic chain-length dependent emission is observed, spanning from blue (n = 1, 2, ∼400 nm) and blue-green (n = 3–5, 500–550 nm) to green-orange (n = 6) and red (n = 7, 8, ∼610 nm) in various regular solvents. Comprehensive spectroscopic and dynamic studies, together with a computational approach, rationalized the associated excited-state structure responding to emission origin. Severing the linkage for DPAC-5 via lipase treatment releases the structural freedom and hence results in drastic changes of emission from blue-green (490 nm) to red (625 nm), showing the brightening prospect of these chemically locked DPAC-n in both fundamental studies and applications.