Ming-De Li

Reversible photocycloaddition reactions of anthracene-based compounds have attracted considerable attention. However, the solid-state cycloaddition mechanism is unclear, and the cycloaddition behavior of X-aggregated anthracene dimers remains unexplored. Herein, we found that 2,3-diethylbenzo[g]quinoxaline (EBQ), which assembles into crossing-stacked anthracene dimers with an −8.8° rotation angle, can undergo single-crystal to single-crystal photocycloaddition, accompanied by photochromism and fluorescence modulation. Detailed analyses via transient absorption spectroscopy and theoretical calculation reveal that the solid-state cycloaddition of EBQ follows a stepwise mechanism: (1) fast structural arrangement from the localized S1 state to the delocalized excimer state upon photoexcitation; (2) intersystem crossing via the S1/T2 crossing point; (3) formation of the first C–C bond via a rate-determining transition state, dominated by intermolecular steric hindrance; and (4) formation of the second C–C bond via the T1/S0 crossing point. Therefore, this work not only confirms the feasibility of the solid-state photocycloaddition of X-aggregated anthracene dimers but also elucidates the solid-state cycloaddition mechanism.

We introduce a supramolecular approach to substantially expand the response wavelength of photoswitchable stilbene( E ) from UVC (274 nm) to NIR‐II (1064 nm) region, which doesn't depend on E ‐to‐ Z photoisomerization. Stilbene( E ) acts as an electron donor and is co‐assembled with a matched acceptor (e.g., F x TCNQ, x = 1/2/4) to form a solid complex with a loose stack and broadband absorption of 250–1100 nm through one‐step mechanochemical synthesis. Reversible green‐to‐yellow chromism is observed for the complex exposed to 808 nm‐light irradiation/heating treatment, which corresponds to the disappearance/appearance of the absorption band of ∼550‐1100 nm. This behavior is attributed to photo‐induced ultrafast torsion (E ) skeleton and resulting destruction of donor‐acceptor π‐π stacking, and subsequent heating‐induced recovery. Besides, the complex can also serve as a UV‐excited fluorescence switch and NIR‐photothermal material. Hence, donor‐acceptor complexation effectively reduces the photo‐activation energy of stilbene( E ) by π‐π interaction and provides a promising route to design a multi‐functional photoswitch with ultra‐broadband light response.

To leverage the synergistic benefits of sunlight‐responsive metalloporphyrin complexes and conductive MXene materials, a Schottky heterojunction comprising tin‐porphyrin (SnTCPP) nanoparticles (NPs) and Nb ₂ C MXene was rationally constructed. Notably, the SnTCPP NPs‐Nb ₂ C Schottky heterojunctions demonstrate exceptional sunlight‐driven catalytic activity toward tetracycline antibiotics and ofloxacin degradation, achieving a removal efficiency of up to 99.9% within 60 min of irradiation in both model wastewater and natural water. The unique energy structure of SnTCPP NPs‐Nb ₂ C facilitates rapid charge transfer while inhibiting the recombination of photogenerated carriers, thereby enhancing the generation of reactive oxygen species, such as holes and superoxide anion radicals, which are the key factors driving tetracycline antibiotics and ofloxacin degradation. Ultrafast spectroscopic results unveil efficient Schottky junction‐mediated ultrafast charge transfer and separation at the SnTCPP NPs‐Nb ₂ C interface. The integrated DFT and liquid chromatography‐mass spectrometry demonstrated the sequential cleavage of tetracycline's functional groups, including the dimethylamino group, phenolic moiety, and tetracyclic ring structure, ultimately leading to the mineralization of tetracycline into harmless small molecules. Notably, the high degradation efficiency can be maintained over multiple consecutive recycling cycles without significant loss of catalytic activity. These studies pave the way for the rational design of next‐generation sunlight‐driven heterojunction catalysts for environmental pollutant remediation.

Polymorphism in covalent organic frameworks (COFs) offers a unique platform to decipher structure–property relationships, yet its impact on excited‐state dynamics remains unexplored. Herein, we construct two chemically identical but topologically distinct 1D and 2D COF polymorphs to correlate framework architecture with photocatalytic performance. Impressively, in H ₂ O ₂ photosynthesis coupled with furfuryl alcohol valorization, the 1D‐TBPP‐COF showed an exceptional H ₂ O ₂ generation rate (18.75 mmol g ⁻¹ h ⁻¹ ) and selective oxidation of furfuryl alcohol to high‐value 6‐hydroxy‐2H‐pyran‐3(6H)‐one (PN) with PN formation rate of 28.14 mmol·g ⁻¹ ·h ⁻¹ , substantially outperforming the 2D‐TBPP‐COF counterpart. Mechanistic investigations revealed that the intercalated dual‐chain edges in 1D‐TBPP‐COF impose steric constraints on aromatic ring rotation, effectively suppressing vibrational relaxation losses and prolonging the charge‐transfer state lifetime. In contrast, the conformationally flexible 2D‐TBPP‐COF permits greater rotational freedom, leading to non‐radiative energy dissipation. This work establishes polymorphism engineering as a powerful strategy to manipulate excited‐state dynamics in COFs for photocatalysis.

Polymorphism in covalent organic frameworks (COFs) offers a unique platform to decipher structure–property relationships, yet its impact on excited‐state dynamics remains unexplored. Herein, we construct two chemically identical but topologically distinct 1D and 2D COF polymorphs to correlate framework architecture with photocatalytic performance. Impressively, in H ₂ O ₂ photosynthesis coupled with furfuryl alcohol valorization, the 1D‐TBPP‐COF showed an exceptional H ₂ O ₂ generation rate (18.75 mmol g ⁻¹ h ⁻¹ ) and selective oxidation of furfuryl alcohol to high‐value 6‐hydroxy‐2H‐pyran‐3(6H)‐one (PN) with PN formation rate of 28.14 mmol·g ⁻¹ ·h ⁻¹ , substantially outperforming the 2D‐TBPP‐COF counterpart. Mechanistic investigations revealed that the intercalated dual‐chain edges in 1D‐TBPP‐COF impose steric constraints on aromatic ring rotation, effectively suppressing vibrational relaxation losses and prolonging the charge‐transfer state lifetime. In contrast, the conformationally flexible 2D‐TBPP‐COF permits greater rotational freedom, leading to non‐radiative energy dissipation. This work establishes polymorphism engineering as a powerful strategy to manipulate excited‐state dynamics in COFs for photocatalysis.

Room temperature phosphorescence (RTP) materials with long luminescence lifetimes and tunable properties are highly desirable for applications in optoelectronics, information encryption, and bioimaging. Although host–guest doping is an effective strategy to achieve high‐performance RTP in most systems, the RTP originates from the guest through host confinement and charge/energy transfer. Activating RTP from the host remains a significant challenge due to inefficient triplet exciton manipulation. Here, we successfully achieved ultralong host RTP (224 ms) in the host–guest doped systems with a controlled triplet state energy gap (Δ E _T ) of 0.36–0.44 eV, which facilitates an endothermic reverse triplet–triplet energy transfer (rTTET) process from the guest to the host, and thereby promotes the repopulation of host triplet excitons. This process establishes a dynamic thermal equilibrium between forward triplet–triplet energy transfer (TTET) and rTTET, leading to thermally activated delayed phosphorescence from the host. As a result, the lifetime of the host's RTP is extended by 1120‐fold (from 0.2 to 224 ms). More importantly, the photoluminescence properties of the host's RTP can be systematically and predictably tuned by varying the Δ E _T , temperature, and doping ratio. This work provides a mechanistic insight and paradigm into the design of RTP materials through intermolecular exciton dynamics.

Room temperature phosphorescence (RTP) materials with long luminescence lifetimes and tunable properties are highly desirable for applications in optoelectronics, information encryption, and bioimaging. Although host–guest doping is an effective strategy to achieve high‐performance RTP in most systems, the RTP originates from the guest through host confinement and charge/energy transfer. Activating RTP from the host remains a significant challenge due to inefficient triplet exciton manipulation. Here, we successfully achieved ultralong host RTP (224 ms) in the host–guest doped systems with a controlled triplet state energy gap (Δ E _T ) of 0.36–0.44 eV, which facilitates an endothermic reverse triplet–triplet energy transfer (rTTET) process from the guest to the host, and thereby promotes the repopulation of host triplet excitons. This process establishes a dynamic thermal equilibrium between forward triplet–triplet energy transfer (TTET) and rTTET, leading to thermally activated delayed phosphorescence from the host. As a result, the lifetime of the host's RTP is extended by 1120‐fold (from 0.2 to 224 ms). More importantly, the photoluminescence properties of the host's RTP can be systematically and predictably tuned by varying the Δ E _T , temperature, and doping ratio. This work provides a mechanistic insight and paradigm into the design of RTP materials through intermolecular exciton dynamics.

In organic donor–acceptor (D-A) materials, a nitrogen atom can serve as a skeleton electron source to tune the inter-/intra-molecular charge transfer (CT) nature and photophysical/photochemical properties. Here, we employ the model molecule stilbene modified with non-/one-/two-nitrogen atoms in the benzene ring skeleton (TSB/TSP/DPE) as a donor and F4TCNQ as an acceptor to synthesize three cocrystals by a one-step mechanochemical method toward NIR photothermal conversion (NIR-PTC). The results show that “One Nitrogen Atom Is Good, Two Are Too Many.” That is, one nitrogen atom in the donor (TSP) is enough to induce optimal performance of the CT effect with the degree of charge transfer of ∼1.16, redshift absorption of ∼2500 nm, and NIR-PTC efficiency of ∼89.4% @ 808 nm. Femtosecond transient absorption spectra exhibit that superior NIR-PTC of TSP-F4TCNQ cocrystal can be attributed to the first ultrafast internal conversion (IC) with a lifetime of 1.7 ± 0.4 ps and subsequent nonradiative decay (NR) via rotation/twisting of cyano-groups out of the plane of central ring of F4TCNQ with a lifetime of 17.1 ± 3.4 ps, followed by the third vibrational relaxation (VR) with a lifetime of 754 ± 220 ps. The individual partition contribution factor of IC/NR/VR channels is resolved to be about 0.33:1.51:1.12 based on a simple linear approximation treatment for the first time. This work provides a simple and potential approach for regulating photophysical properties of D-A cocrystals by introducing a skeleton electron source.

Ultrafast all-optical modulators are central to the advancement of next-generation photonic computing and signal-processing systems. However, the intrinsic electron–phonon relaxation bottleneck in plasmonic materials has long constrained modulation speeds to the picosecond regime, hindering the realization of sub-100 fs modulation. Here, we report a metastructured silver–single-crystal silicon nanodisk antenna that delivers experimentally resolved sub-100 fs all-optical modulation. Distinct from conventional planar metal–semiconductor junctions, the nanodisk architecture spatially co-localizes plasmonic energy deposition with the metal–semiconductor transfer boundary within a nanoscale-confined volume. This configuration markedly shortens hot-carrier transport pathways and preferentially activates interfacial carrier extraction during the earliest relaxation stage, thereby establishing an interface-dominated modulation pathway that precedes electron–phonon thermalization. By enabling modulation on timescales comparable to intrinsic electronic response limits, this work establishes a physical foundation for ultrafast photonic modulation, including femtosecond free-space photonic computing architectures, temporal optical gating, and other ultrafast systems constrained by carrier or cavity lifetimes.

We studied the intersystem crossing (ISC) and triplet states of thionated perinones to assess how the thionation of the carbonyl group in a chromophore affects these processes or properties. The thionated compounds show red-shifted absorption and strongly quenched fluorescence compared to the oxo-counterparts. Femtosecond transient absorption spectra show fast ISC kinetics (0.31–1.92 ps⁻¹) for the thionated chromophores. Nanosecond transient absorption spectra demonstrated short triplet excited state lifetimes (0.62–11.5 µs) for the thionated perinones, which is unusual for heavy atom-free small organic molecules. Time-resolved electron paramagnetic resonance spectroscopy following photoexcitation shows inversion of the electron spin polarization pattern of the triplet state, which is resulted from the overpopulation of one sublevel and its fast decaying with respect to the other two sublevels of the T₁ state. Spectral simulation shows that the T_z sublevel decays 25-time faster (1.0 × 10⁴ s⁻¹) than the T_x and T_y sublevels (ca. 4.0 × 10² s⁻¹). Interestingly, zero field splitting (ZFS) D parameters (ca. 0.268 cm⁻¹) was observed for S3, which is unusually large for an organic molecule. These results demonstrated the relationship between the thionation and the enhanced ISC, the triplet state lifetimes, as well as the triplet-state electron spin dynamics, it is useful for the development of heavy-atom-free triplet photosensitizers.