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. 2025 Aug 7;147(33):30390–30400. doi: 10.1021/jacs.5c09956

Electrochemical Annulation of Phenothiazines with Alkynes: Access to Anti-Kasha Triple-Emission, Light-Sensitive, and Room-Temperature Phosphorescent Materials

Xianhui Yang 1, Danni Yang 1, Bijin Li 1,*
PMCID: PMC12372794  PMID: 40772540

Abstract

Novel anti-Kasha triple-emission materials, light-sensitive materials, and ultralong room-temperature phosphorescent materials were synthesized by an efficient electrochemical synthesis method for the first time. The experimental data and theoretical calculations demonstrate the anti-Kasha triple-emission characteristics of the phenothiazinium salts. These characteristics enable three-channel emission intensity ratio imaging for visualizing intercellular architectures and endow the ability to specifically target the mitochondria of living cells. Furthermore, the novel light-sensitive materials demonstrate a pronounced red shift upon light irradiation. Additionally, the novel phenothiazine-based ultralong room-temperature phosphorescent materials exhibit an extraordinarily long lifetime and a distinctive afterglow, highlighting significant potential for encryption applications in binary coding systems.

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Introduction

Luminescent materials have significantly enhanced the quality of human life through their widespread applications in field-effect transistors, organic light-emitting diodes, security systems, optoelectronic devices, bioprobes, chemosensors, etc. − In recent years, novel luminescent materialsparticularly anti-Kasha fluorescence materials, light-sensitive materials, and ultralong organic room-temperature phosphorescent (UORTP) materialshave garnered substantial research interest. ,− These materials promise to drive innovations in optical sensing, lighting technologies, and bioimaging. ,− Anti-Kasha fluorescence molecules exhibit emission from high energy excited states (S n , n ≥ 2), making them valuable for precise analyses in basic life sciences and optoelectronic device development. − Light-sensitive materials, as “smart” stimulus-responsive systems with optically tunable color properties, have demonstrated critical applications in anticounterfeiting, optical information processing, data security, and biosensing. ,− UORTP materials, characterized by long-lived triplet excitons and environmentally friendly, chemically modifiable structures, have shown intriguing potential in information storage, emergency signage, anticounterfeiting technologies, bioimaging, and advanced optoelectronics. − Consequently, developing these material classes has attracted interdisciplinary attention from both scientific and engineering communities. ,− Notably, however, the advancement of these cutting-edge luminescent materials remains challenged by inherent limitations in the photophysical properties of organic molecules. ,−

Anti-Kasha fluorescence materials typically exhibit a large energy separation between the S n and S n–1 states (n ≥ 2), which leads to a relatively slow internal conversion (IC) process from S n to S n–1. − Consequently, the radiative emission rates of the S n state can effectively compete with internal conversion (Scheme ). The fundamentals of light-sensitive molecules involving covalent interactions and noncovalent bonding include amphiphilic interactions, π-π stacking, electrostatic forces, and hydrogen bonding. Representative light-sensitive molecules include azobenzene, spiropyran, diarylethene, dihydroazulene, and dimethyl­dihydro­pyrene, which undergo E/Z photoisomerization or ring-opening/ring-closing photocyclization reactions. − For UORTP materials, strong spin–orbit coupling (SOC) is typically demanded. ,,− This is to guarantee a high intersystem crossing (ISC) efficiency. Meanwhile, a sufficiently large energy gap ΔE S1T1 (>0.3 eV) is needed to suppress reverse intersystem crossing (RISC). Moreover, reducing the nonradiative transition rate requires strategies such as metal–organic frameworks, crystal engineering, host–guest systems, or polymer doping. Therefore, drawing on these theoretical foundations, we will develop innovative luminescent materials.

1. Design of Anti-Kasha Triple-Emission Materials, Light-Sensitive Materials, and Ultralong Organic Room-Temperature Phosphorescent (UORTP) Materials Based on Phenothiazinium Salts.

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Building on our prior research, we have discovered that phenothiazinium salts display anti-Kasha dual-emission properties. − Notably, no anti-Kasha triple-emission fluorescence materials with phenothiazines have been documented to date. ,, Herein, taking phenothiazine pyridinium salt as the core skeleton and based on density functional theory (DFT) calculations, we designed the anti-Kasha triple-emission fluorescence compound 3a and UORTP molecule 5a (Scheme , section II, Supporting Information (SI)). Theoretical calculations reveal that compound 3a exhibits two relatively large energy gaps between adjacent excited states, with ΔE values of 0.67 eV for S3 → S2 and 0.55 eV for S2 → S1 (Scheme ). The compound 5a exhibits a relatively large singlet–triplet energy gap ΔE S1T1 (0.31 eV). Additionally, it shows strong spin–orbit coupling (SOC) matrix elements ((S0, T1) = 28.9 cm– 1, (S1, T1) = 61.6 cm– 1, (S1, T2) = 259.0 cm– 1, (S1, T3) = 251.0 cm– 1), which imply the presence of effective intersystem crossing (ISC) channels and that triplet excitons can decay directly via phosphorescence (Scheme ). Given that phenothiazine compounds are frequently used as photosensitizers to oxidize chloride ions into chlorine radicals (Scheme ), we aim to develop 4a as a photosensitizer for chloride ion oxidation. This process is expected to alter the ionic bonds within the molecule and induce changes in the molecular packing mode, thereby triggering distinct fluorescence variations.

Subsequently, we plan to develop an efficient protocol for the synthesis of target compounds 3a–5a. Electrochemical synthesis has emerged as a highly attractive synthetic tool owing to its inherent advantages, such as utilizing traceless electric current as a green reagent, exhibiting environmental benignity, ensuring operational simplicity, offering ease of scalability, demonstrating unique chemoselectivity and tunability, and delivering economic efficiency through the use of inexpensive and recyclable electrodes. − Therefore, we specifically designed a ruthenium-catalyzed electrochemical C–H activation and annulation of phenothiazine-3-pyridines strategy to construct the target phenothiazinium salts.

Results and Discussion

Condition Optimization and Substrate Scope

We used 10-methyl-3-(pyridin-2-yl)-10H-pheno­thia­zine (1a) and 1,2-diphenyl­acetyl­ene (2a) as model substrates to evaluate the electrochemical ruthenium-catalyzed C–H bond activation and annulation strategy (Table S1). After screening several parameters (see SI, Table S1), we got 3a with a moderate yield of 64% under the standard reaction conditions (electrode Pt/graphite felt, 5.0 mol % [RuCl2(p-cymene)]2, 2.0 equiv NaOAc, in HFIP/H2O/DCM (3:1:1) at 60 °C for 6 h with a constant current of 3 mA in a user-friendly undivided three-necked round-bottomed flask (Scheme S3)). Furthermore, by extending the reaction time to 24 h, we obtained 4a with a good yield of 83% (Scheme ).

2. Synthesis of Phenothiazinium Salts .

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a PMMA films (1.0 wt %).

b PVA films (1.0 wt %). λex = 370 nm. Excitation slit: 2.5 nm, emission slit: 1.0 nm. PMT voltage = 700 V.

c Synthesis 3a–3g: 1 (0.05 mmol), alkynes 2 (0.10 mmol), [RuCl2(p-cymene)]2 (5 mol %), NaOAc (2.0 equiv), HFIP/H2O/DCM (3:1:1), 60 °C, 3.0 mA, 6 h. Synthesis 4a–4s: 1 (0.05 mmol), alkynes 2 (0.10 mmol), [RuCl2(p-cymene)]2 (5 mol %), NaOAc (2.0 equiv), HFIP/H2O/DCM (3:1:1), 60 °C, 3.0 mA, 24 h. Absorption maximum in CH2Cl2 (5.0 × 10–5 M). Emission maximum in CH2Cl2 (1 × 10–6 M). Synthesis 5a–5e: 3, 4 (0.1 mmol), CH2Cl2, acetic acid, 60 °C, 24 h.

Given that this method represents a novel strategy for the synthesis of quino­lizino­pheno­thiazin-5-ium and its derivatives, it presents a unique avenue for facile and efficient access to novel organic luminescent frameworks that are otherwise challenging to construct via traditional synthetic pathways. The substrate scope of electrochemical synthesis deserves further investigation. Subsequently, various phenothiazines, phenoselenazine, and carbazole were used to annulate with alkynes, providing the desired products 3a–4s in good to excellent yields under the corresponding optimized electrochemical synthesis conditions. The structure of compound 4o was further confirmed by 1H–1H nuclear Overhauser effect spectroscopy (Figure S56). Various functional groups such as methyl (3e, 4e, 4h, 4l, 4r), ethyl (3f, 4f, 4m), butyl (3c, 4c, 4i, 4n, 4s), fluoro (4p, 4q), carbazole (4i), and trifluoromethyl (3g–3i, 4g, 4j) were well tolerated in the reaction. These compounds, as novel fluorescent frameworks, feature prominent fluorescence emission (Scheme ).

In the protocol, electrodes can be recycled, and mass-free electrons serve as oxidants, eliminating the need for stoichiometric metal oxidants. This process simultaneously releases hydrogen gas without generating ecologically hazardous waste. In traditional oxidation cyclization reactions, rhodium and iridium metals are often used as catalysts. Ruthenium is significantly cheaper than rhodium and iridium. Moreover, since only a small amount of this catalyst is required, it offers considerable economic advantages. The electrochemical synthesis strategy that we have developed possesses a certain degree of economic and environmental friendliness.

Furthermore, a plausible catalytic cycle of electrochemical ruthenium-catalyzed C–H activation and annulation reaction is proposed (see SI, Figure S5). Initially, compound 1 coordinates with ruthenium­(II) species, and C–H bond activation occurs to afford five-membered ruthenacycle intermediate I. Then, alkyne 2a coordinates with intermediate I to give intermediate II, and migratory insertion into the C–Ru bond subsequently occurs to form seven-membered ruthenacycle III. Finally, intermediate III undergoes reductive elimination to give the cyclization product 3, releasing H2 as the byproduct at the cathode and generating RuI species. The RuI species are reoxidized to ruthenium­(II) species at the anode. During the catalytic process, CH2Cl2 is reduced to offer chloride anions at the cathode, which are used to make the final salt. − In addition, the cyclization product 3 could be further oxidized to generate sulfoxide compounds 4 at the anode.

1. Application in Anti-Kasha Triple-Emission Materials

Single-molecule triple-emission fluorescence materials remain rare yet highly sought after across materials science, biology, and medicine. − This is because triple-emission molecules serve as promising candidates for organic single-molecule white-light emitters while holding great potential for enabling ultraprecise analysis in fundamental life science research. Subsequently, the photophysical properties of phenothiazinium salts 3a–3i were further investigated (Figures S6, S7, S9, and S10, section VIII, SI). They exhibit obvious triple-emission, and their emission wavelengths are located in the range of blue to orange (417–605 nm) in dichloromethane (Figure S7). Compound 3a was selected as a representative, and its fluorescence properties were further analyzed. It displays three major emission peaks at 419 (τ = 1.48 ns), 502 (τ = 4.21 ns), and 587 nm (τ = 2.38 ns) in the steady state spectrum with the white-light CIE1931 coordinates (0.34, 0.35) and a high quantum yield of 19% in dichloromethane (Tables S4 and S5, SI). In addition, compound 3a still exhibits distinct triple-emission peaks at 407 (τ = 1.06 ns), 473 (τ = 5.24 ns), and 564 nm (τ = 4.53 ns) with the white-light CIE1931 coordinates (0.34, 0.37) and a quantum yield of 5% in the poly­(methyl methacrylate) (PMMA) film (0.02 wt %) (Figure S12, Tables S4 and S5).

To gain insight into the triple-emission mechanism, the anti-Kasha characteristics of 3a and 3b were further investigated via excitation-wavelength-dependent fluorescence experiments, emission-wavelength-dependent excitation experiments, and time-dependent density functional theory (TD-DFT) calculations (Figure , section II, SI). In the emission-wavelength-dependent excitation spectra of 3a, the intensity of the shorter excitation band at ∼375 nm gradually diminished, while the longer excitation band at ∼450 nm exhibited a slight red shift. Meanwhile, this band was accompanied by a concomitant intensity enhancement as the emission wavelength increased (Figure S9). Furthermore, in the excitation-wavelength-dependent emission experiments, the intensity of the emission at the longest yellow wavelength remained constant, while the intensities of the shorter green emission and the shortest blue emission exhibited a gradual increase as the excitation wavelength was tuned from 330 to 370 nm (Figure a). Transient absorption experiments on compound 3a were conducted, revealing that it has short fluorescence lifetimes with no long-lived species detected (Figure S8). For compound 3b, upon lower energy excitations, the intensity at the shortest blue emission wavelength exhibits a gradual decrease, while the intensity at the middle green emission wavelength undergoes a gradual increase and the intensity at the longest yellow emission first remains unchanged before increasing significantly (Figure d). These experiments demonstrate that such compounds exhibit anti-Kasha behavior with the relative intensity of the triple-emission being highly dependent on the excitation wavelength. Additionally, the triple fluorescence emissions originate from distinct excited states (Figure , Figure S10). Furthermore, the triple-emission of 3a and 3b includes the longest wavelength from low-lying singlet state emission (S1 → S0, 3a: f = 0.6857; 3b: f = 0.6928), the green emission wavelength in the middle from high-lying singlet state emission (S2 → S0, 3a: f = 0.0700; 3b: f = 0.0046), and the shortest wavelength from high-lying singlet state emission (S3 → S0, 3a: f = 0.4853; 3b: f = 1.0754, Figure ).

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The triple emission characteristics of 3a–3b and their possible luminescent mechanisms. (a, d) Excitation-wavelength-dependent fluorescence spectra of 3a (1 × 10–6 M) and 3b (1 × 10–6 M). (b, e) Molecular orbitals of the S0, S1, S2, and S3 states of 3a and 3b. (c, f) Jablonski diagrams illustrating the anti-Kasha triple-emission mechanism of 3a and 3b.

The relatively large energy gap ΔE(S3 → S2) values (3a: 0.67 eV, 3b: 0.48 eV) and ΔE(S2 → S1) values (3a: 0.55 eV, 3b: 0.78 eV) could effectively inhibit the partial internal conversion (IC) processes from the S3 to S2 state and from the S2 to S1 state. This inhibition enables the fluorescence emission from the S3 and S2 states to compete favorably with the IC (Figure , Figure S1).

Triple-emission imaging has garnered significant attention across medicine, biology, and related scientific disciplines. This technique is highly valued for its ability to provide simultaneous trichannel information, which can notably enhance the imaging resolution and detection sensitivity of optical imaging systems. Moreover, it plays a pivotal role in the development of high-performance organelle imaging reagents, driving advancements in the field of bioimaging. Subsequently, the cytotoxicity experiment of 3a was carried out, and almost no toxicity was observed in HeLa cells (Figure S47). Further staining experiments of 3a were conducted on HeLa cells, and fluorescence signals were imaged using confocal laser scanning microscopy (CLSM) (Figure , Figures S48 and S49). Upon excitation at 405­(S3), 488 (S2), and 552 nm (S1), CLSM revealed distinct signal distributions in the blue, yellow, and red spectral regions (Figure a–c,e–g). The emission intensity ratio maps were generated by combining the corresponding fluorescence imaging from the S3, S2, and S1 emission channels using ImageJ software (Figure d,h). These maps clearly reveal cellular structures and intercellular architectures (Figure d,h). Nevertheless, the intercellular structure could not be observed constantly in S3, S2, or S1 emission one-channel images (Figure a–c,e–g). The experimental results indicate that the multichannel ratio maps contain more comprehensive cellular features and information, as opposed to merely reflecting the textural characteristics of single-channel images (Figure d,h).

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Fluorescence microscopy images of HeLa cells incubated with 3a (2 μm) for 0.5 h at 37 °C. (a, e) Fluorescence microscopy images from channel 1 at 425–470 nm (excitation 405 nm). (b, f) Fluorescence microscopy images from channel 2 at 498–550 nm (excitation 488 nm). (c, g) Fluorescence microscopy images from channel 3 at 570–700 nm (excitation 552 nm). (d, h) The emission intensity ratio of (a–c)/(e–g) of HeLa cells (image generation by ImageJ software). The scale bar is 25.0 μm. Circle: marks out the cellular structures and intercellular architectures.

Furthermore, costaining experiments were conducted on HeLa cells using 3a and commercially available dyes to investigate subcellular localization, which included 3,3′-diocta­decyl­oxa­carbo­cyanine perchlorate (DiO, a membrane-specific tracker), ER-Tracker Green (an endoplasmic reticulum-specific tracker), Lyso-Tracker Green (a lysosome-specific tracker), Mito-Tracker Deep Red 633, and Mito-Tracker Green (mitochondria-specific trackers) (Figure , Figures S50–S52). The costaining experiment results indicated that 3a can specifically target mitochondria because it has higher Pearson correlation coefficients (r) (0.96/0.89) in the mitochondria than in the cell membranes, endoplasmic reticulum, and lysosomes (Figure , Figures S50–S52).

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Costaining experiments. (a) Fluorescent image of HeLa cells cultured with 3a (2 μm) (λex = 552 nm, λem = 570–700 nm). (b) Fluorescent image of HeLa cells with Mito-Tracker Green (λex = 488 nm, λem = 508–540 nm). (c) Merged image of (a, b). (d) The Pearson correlation coefficient r = 0.96. (e) Fluorescent image of HeLa cells cultured with 3a (2 μm) (λex = 552 nm, λem = 570–600 nm). (f) Fluorescent image of HeLa cells with Mito-Tracker Red (λex = 633 nm, λem = 650–700 nm). (g) Merged image of (e, f). (h) The Pearson correlation coefficient r = 0.89; The scale bar is 25.0 μm.

2. Application in Light-Sensitive Materials and Photocatalysts

Light-sensitive materials have garnered significant attention across diverse domains, such as optoelectronic memory devices, optical switching, and information storage. − Subsequently, the light-sensitive behaviors of compounds 4a–4s were investigated. Upon irradiation with 365 nm UV light, the 1 wt % PMMA films containing compounds 4a–4s exhibited a significant red shift in their emission spectra, with the emission color transitioning from blue-green (4a: 507 nm; 4b: 498 nm; 4h: 484 nm) to yellow (4a: 560 nm; 4b: 600 nm; 4h: 600 nm; Table S3, Figure S13). The PMMA films corresponding to 4a, 4b, and 4h exhibited red shifts of approximately 53, 102, and 116 nm, respectively (Figure a, Figure S13, Table S3). Under illumination, fluorescence undergoes a gradual red shift process (Figures S18 and S19). The fluorescence lifetime shows no significant change, consistently at the nanosecond level (4a: 6.0 → 7.6 ns; 4b: 5.0 → 4.6 ns; Table S4). Additionally, the fluorescence quantum yield has a slight decrease (4b: 10.8% → 5.4%; Table S5). The red shift in fluorescence emissions can be attributed to 4b acting as a photosensitizer, which oxidizes chloride ions and induces changes in molecular packing modes. , In addition, after the 4b film material changed color upon exposure, it was dissolved again in dichloromethane and reformed into a PMMA film, which restored the original maximum emission wavelength (Figure S20).

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(a) Experimental emission spectra of compounds 4a and 4b in the PMMA films before and after UV irradiation. (b) Corresponding CIE1931 of compounds 4a and 4b in the PMMA films before and after UV irradiation. Fluorescence images of 4a and 4b were obtained before and after UV irradiation.

To gain an in-depth understanding of 4a and 4b as photosensitizers, we conducted the chlorination of unactivated C­(sp3)–H bonds in cyclohexane and identified the products via gas chromatography–mass spectrometry (GC-MS) (Figure a, Table S8, Figures S54 and S55). When 5 mol % 4a and 5 mol % 4b were employed as photocatalysts, the respective yields reached 92% and 91% (Figure a). Moreover, compound 4b was used as a photocatalyst to cleave the strong aryl chloride bond, generating an aryl radical and achieving C–C cross-coupling upon light excitation (Figure b, Table S7, Figure S53). Furthermore, cyclic voltammetry experiments of 4a and 4b showed one reduction and multiple oxidation peaks in CH2Cl2 electrolyte solutions (Figures S45 and S46). Hence, compounds 4a and 4b could be used as photocatalysts in C–H bond functionalization reactions. These results will provide further guidance for the molecular design principles and practical applications of organic photocatalysts incorporating phenothiazinium salts.

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(a) The photocatalysis chlorination of unactivated C­(sp3)–H bonds of cyclohexane. (b) The photoreduction reaction achieves C–C cross-coupling.

3. Application in Room-Temperature Phosphorescent Materials

The ultralong organic room-temperature phosphorescent (UORTP) molecules 5a–5e were further synthesized with good yields using electrochemical products 4a, 4j, and 3g–3i as substrates (Scheme ). Notably, compounds 5a–5c exhibited ultralong RTP lifetimes of 156.7, 388.8, and 614.2 ms, with quantum yields ranging from 7.0% to 8.7%, in 1.0 wt % PMMA films (Scheme , Figure a, Figures S39–S42, Tables S4 and S5, SI). Additionally, compounds 5a–5e exhibited ultralong RTP lifetimes of 103.2, 204.2, 566.0, 845.2, and 677.2 ms in poly­(vinyl alcohol) (PVA) films, respectively (Scheme , Figures S39–S42, Table S4). In the temperature-variable PL spectra for 5c in PVA film (Figure b), as the temperature decreases, the emission peak gradually increases. Additionally, the phosphorescence lifetime also gradually increases with a decrease in temperature (Figure c). Upon turning off the UV light, the corresponding film exhibited a green afterglow lasting up to 7 s (Figure d). Further comparative analysis of the instantaneous spectra and delayed spectra (1 ms) for compounds 5a–5e in 1.0 wt % PMMA films was performed. The results indicated that the films of compounds 5a and 5b predominantly showed phosphorescence emissions, while compounds 5c–5e exhibited simultaneously coexisting phosphorescence and fluorescence emissions (Figures S28–S30).

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(a) Phosphorescence lifetime decay curves of 5c in a PMMA film (1.0 wt %). (b) Temperature-variable PL spectra of 5c in PVA film (1.0 wt %). (c) Temperature-dependent time-resolved phosphorescence decay curves of 5c in a PVA film (λem = 530 nm). (d) Photographs of four-leaf clover patterns of 4a and 5a–5c taken before and after turning off 365 nm UV excitation. (e–i) Schematic diagram of encryption and decryption processes in the binary coding system.

The PVA films of 4a and 5a–5c were further fabricated into four-leaf clover patterns (Figure d). Upon turning off the UV light, distinct changes in the leaves became readily evident. Notably, the leaves prepared with 5c exhibited an afterglow that persisted for up to 7 s. Leveraging the outstanding phosphorescence properties of the doped films, we further explored their potential applications in the encryption field. In a binary number system, signals “1” and “0” are defined as the emission occurrence and cessation of the emissive dot, respectively. The PVA films of 4a and 5a–5c were fabricated into a 16-hole binary coding system (equivalent to a 4-bit binary architecture). Under UV excitation, all dots emitted intense light immediately. Four seconds after UV excitation ceased, some dots faded out, and the correct binary code was decoded as “911” (the emergency call number) according to the binary encoding rules (Figure i). This result indicates that these novel phenothiazine pyridinium salts possess excellent phosphorescent properties, making them suitable for advanced information security applications.

To further evaluate the possible phosphorescence emission, the energy levels and spin–orbit coupling (SOC) values between the singlet and triplet states of 5c were calculated (Figure , Figure S4, section II, SI). The theoretical S1 of 5c was 2.74 eV (452 nm), which is close to the experimental value of 2.73 eV (454 nm) in the PMMA film (Figure b, Figures S4 and S25). The T1 value of 5c was 2.31 eV (537 nm), which is in good agreement with the corresponding low-temperature phosphorescence measurement value of 2.30 eV (540 nm) for 5c@PVA at 80 K (Figures b and b, Figure S25). Furthermore, the relatively large spin–orbit coupling (SOC) matrix elements (5a: ξ­(S1, T2) = 259.0 cm–1, ξ­(S0, T1) = 28.9 cm–1; 5b: ξ­(S1, T2) = 260.2 cm–1, ξ­(S0, T1) = 24.7 cm–1; 5c: ξ­(S1, T3) = 258.9 cm–1, ξ­(S0, T1) = 33.3 cm–1) indicate the presence of effective intersystem crossing (ISC) channels in compounds 5a–5c (Figure , section II, SI). Consequently, triplet excitons in these systems can decay directly via phosphorescence emission.

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Molecular orbitals, energy levels, and SOC values between singlet and triplet states of 5b (a) and 5c (b).

Conclusion

In conclusion, we have successfully developed anti-Kasha triple-emission materials, light-sensitive materials, photocatalysts, and ultralong room-temperature phosphorescent materials for the first time via an efficient electrochemical synthesis strategy. The ruthenium-catalyzed electrochemical C–H activation and annulation of phenothiazine-3-heterocycle strategy was used to construct a library of structurally diverse phenothiazinium salts for the first time. Moreover, the novel anti-Kasha phenothiazinium salts display unique triple-emission characteristics, which are efficiently endocytosed by HeLa cells, thus enabling triple-emission imaging in living cells. For the first time, these salts are applied in three-channel emission intensity ratio imaging to visualize cellular structures and intercellular architectures, and they can specifically target the mitochondria of living cells. Furthermore, the novel phenothiazinium salts display notable light-sensitive properties with a significant red shift and are found to serve as photocatalysts in C–H bond functionalization reactions. In addition, the novel ultralong room-temperature phosphorescent materials based on phenothiazines exhibit an ultralong lifetime and prominent afterglow, which hold great potential for applications in encryption. This work presents a straightforward strategy for synthesizing structurally diverse phenothiazinium salts, thereby opening up promising avenues for the discovery of three-channel emission intensity ratio imaging materials, light-sensitive materials, and ultralong room-temperature phosphorescent materials.

Supplementary Material

ja5c09956_si_001.pdf (19.9MB, pdf)

Acknowledgments

We gratefully acknowledge the project supported by graduate research and innovation foundation of Chongqing China (Grant No. CYs25081), the fundamental research funds for the central universities (No. 2024IAIS-QN001, 2024CDJQYJCYJ-001; 2024CDJXY002), the Natural Science Foundation of Chongqing (CSTB2022NSCQ-MSX1123), the Chongqing Talents: Exceptional Young Talents Project (cstc2021ycjh-bgzxm0067), the Venture & Innovation Support Program for Chongqing Overseas Returnees (cx2022061), the Hongshen Young Scholars Program from Chongqing University (0247001104426), and Xiaomi Young Scholar for financial support. We thank Mrs. Chuanyao Yang (Chongqing University analysis and testing center) for conducting the fluorescence test.

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/jacs.5c09956.

  • Detailed descriptions of all experiments: experimental procedures, detailed materials and methods, DFT calculation, plausible catalytic cycle, photophysical properties, excited state lifetimes, photoluminescence quantum yields, electrochemistry properties, cell imaging experiments, photocatalytic reactions, experimental data, and NMR spectra of all products (PDF)

The authors declare no competing financial interest.

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