Jianzhang Zhao

4,4‐Difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) derivatives have gained significant attention for various optoelectronic and biomedical applications due to their tunable photophysical and electrochemical properties. Herein, we report three phenothiazine‐functionalized meso ‐anisyl BODIPYs ( BDPZ1 – BDPZ3 ), synthesized via Suzuki cross‐coupling reactions, incorporating phenothiazine ( BDPZ1 ), formyl‐substituted phenothiazine ( BDPZ2 ), and cyano‐substituted phenothiazine ( BDPZ3 ) at the α ‐positions of the BODIPY unit. These α ‐substituted BODIPYs exhibit strong absorption in the visible region, with absorption onset extending toward longer wavelengths. The presence of electron‐withdrawing groups on the phenothiazine units results in blueshifted absorption maxima for BDPZ2 and BDPZ3 compared to BDPZ1 . The electrochemical studies reveal multiple redox processes, with BDPZ2 and BDPZ3 exhibiting anodically shifted first‐ and second‐oxidation potentials relative to BDPZ1 , consistent with the reduced donor strength of the substituted phenothiazines. Spectroelectrochemical analysis reveals the emergence of new NIR absorption peaks upon oxidation. Notably, BDPZ1 – BDPZ3 do not exhibit intrinsic triplet states; instead, their triplet states are accessed via intermolecular photosensitization with 2,6‐diiodoBodipy, giving triplet lifetimes of 60–118 μs as determined by nanosecond transient absorption spectroscopy. This study highlights how variations in the phenothiazine substituents influence the photophysical and electrochemical properties and excited‐state behavior of the BODIPYs, providing valuable insights for designing BODIPY‐based materials for optoelectronic applications.

The photophysics of a series of Schiff base–BF₂ complexes was investigated using steady-state and femtosecond/nanosecond transient absorption spectroscopy, as well as theoretical computations. The native chromophore has a weak fluorescence and a short fluorescence lifetime (1 state, which decays rapidly through an efficient non-radiative decay channel, possibly geometry torsion. We also studied a Schiff base–BF₂ complex with a twisted molecular structure, which showed a similarly short S₁ state lifetime (2 complexes to be ca. 20 μs, which is much shorter than that of the Bodipy chromophore (100–800 μs). Based on femtosecond transient absorption spectra, we inferred that the decay of the emissive S₁ state takes about 17–20 ps, leading to a non-emissive (dark) state, followed by the formation of a long-lived non-emissive singlet excited state. Theoretical computations demonstrated large spin–orbit coupling matrix elements (SOCMEs, up to 29 cm⁻¹), but the fast non-radiative relaxation of the S₁ state inhibits ISC. Thus, we propose that the fast internal conversion inhibits ISC of the iodo-containing molecules. A theoretical study of the zero-field splitting (ZFS) parameters of the triplet state indicates that the ZFS D parameter (45 cm⁻¹) was overestimated for the iodo-containing compounds, whereas a reasonable value was obtained for the iodo-free compounds (ca. 0.03–0.06 cm⁻¹).

The non‐Boltzmann population of the triplet sublevels in Pt(II)‐Schiff base complexes, and other phosphorescent transition metal complexes, exhibits large zero‐field splitting (ZFS, ∼25 cm ⁻¹ ), preventing a time‐resolved electron paramagnetic resonance (TREPR) study. To investigate the intersystem crossing (ISC) electron spin selectivity of the Pt(II) complexes, we attached a perylene unit as a triplet energy acceptor. Our method relies on the conservation of spin angular momentum during the ultrafast intramolecular triplet–triplet energy transfer (TTET) from the metal‐to‐ligand charge transfer ( ³ MLCT) state to the ³ Pery state of the appended perylene unit, which has a small ZFS (0.05 cm ⁻¹ ) and can be studied with an X‐band TREPR spectrometer. TTET occurs within ∼1 ps. TREPR spectra detected no signal from the native complex, while the modified complex showed the ³ Pery state spectrum with an electron spin polarization (ESP) pattern ( e , a , e , a , e , a ), distinct from the spin‐orbit coupling (SOC)‐generated ³ Pery state ( e , e , e , a , a , a ). Based on the orientation of the two units, the population ratios of the ³ MLCT sublevels were deduced as P _x : P _y : P _z = 0.58:0.22:0.20 (in acceptor's coordinates). Our approach offers a novel way to deduce the ISC spin selectivity in phosphorescent transition metal complexes.

The non‐Boltzmann population of the triplet sublevels in Pt(II)‐Schiff base complexes, and other phosphorescent transition metal complexes, exhibits large zero‐field splitting (ZFS, ∼25 cm ⁻¹ ), preventing a time‐resolved electron paramagnetic resonance (TREPR) study. To investigate the intersystem crossing (ISC) electron spin selectivity of the Pt(II) complexes, we attached a perylene unit as a triplet energy acceptor. Our method relies on the conservation of spin angular momentum during the ultrafast intramolecular triplet–triplet energy transfer (TTET) from the metal‐to‐ligand charge transfer ( ³ MLCT) state to the ³ Pery state of the appended perylene unit, which has a small ZFS (0.05 cm ⁻¹ ) and can be studied with an X‐band TREPR spectrometer. TTET occurs within ∼1 ps. TREPR spectra detected no signal from the native complex, while the modified complex showed the ³ Pery state spectrum with an electron spin polarization (ESP) pattern ( e , a , e , a , e , a ), distinct from the spin‐orbit coupling (SOC)‐generated ³ Pery state ( e , e , e , a , a , a ). Based on the orientation of the two units, the population ratios of the ³ MLCT sublevels were deduced as P _x : P _y : P _z = 0.58:0.22:0.20 (in acceptor's coordinates). Our approach offers a novel way to deduce the ISC spin selectivity in phosphorescent transition metal complexes.

Rigid polyimide specialty plastics combine excellent thermal, mechanical, and chemical resistance, but the stability of the imide group makes closed-loop recycling difficult. Here, we report a strategy for constructing rigid polyimide backbones through solution-state, UV-driven [2 + 2] cycloaddition polymerization of N-aromatic bithiomaleimides. The resulting polymers can be depolymerized thermally to enable closed-loop recycling. Photophysical studies and photopolymerization kinetics have confirmed that only bithiomaleimides containing a diphenyl sulfone linker can be used to construct rigid Poly(S-BMS). The platform was further programmed through side-chain engineering, and the mild photopolymerization conditions showed broad compatibility with functional groups. A series of functionalized polymers were prepared by one-pot copolymerization. In particular, BMSPB-85-C-7.5-F-7.5 combined high tensile strength (57.1 MPa) with a low dielectric constant (k = 2.25 at 1 GHz), demonstrating the tunability of the Poly(S-BMS) system. Using dense hydrogen-bond engineering, we also designed Poly(S-BMSC), a recyclable polyimide adhesive based on this platform. Poly(S-BMSC) exhibited strong bonding to aluminum (LSS = 1.30 MPa) and copper (LSS = 1.21 MPa) substrates. Importantly, Poly(S-BMS) showed thermal reversibility, with more than 88% monomer recovery within 4 h at 160 °C and efficient cycling over at least five cycles. These findings support Poly(S-BMS) as a promising molecular platform for recyclable polyimides with potential utility as low-dielectric layers in flexible circuits and temporary bonding materials in semiconductor processing.

Continuous expansion of photoredox catalysis to other fields, like biology and material science, requires chromophores able to work under different environments. The successful introduction of metallocorroles as triplet photosensitizers and electrocatalysts is due to the facile opportunities for tuning both their redox potentials and optical excitation energies. The current studies focused on demonstrating the viability of a large variety of metal complexes chelated by the same corrole as photoredox catalysts for decarboxylative fluorination. One conclusion is that the long triplet state lifetime of the phosphorus and antimony corroles contributes to the better catalytic performance relative to the classical photoredox catalyst Ru(bpy)₃²⁺. This comes into play by 100-times larger catalytic turnover frequencies (TOFs) and lower catalyst loading. Also illustrated, on top of mechanism of action studies and the isolation of a very reactive reaction intermediate, is that these catalysts are useful for decarboxylative fluorination of common water-polluting drugs via yellow light irradiation.

We report the synthesis and characterization of the photophysical characterization of a series of rhodamine (Rho)–perylenebisimide (PBI) electron donor–acceptor dyad/triads containing flexible alkyl spacers (ethylene or hexylene chains). Steady-state absorption and emission, femtosecond and nanosecond transient absorption (fs-TA and ns-TA), cyclic voltammetry, triplet–triplet energy transfer (TTET) experiments and DFT/TD-DFT calculations were combined to elucidate the excited-state dynamics. fs-TA spectral study indicates fast decay of the S₁ state and formation of the ³PBI state (0.32–663 ps), which is supported by the ns-TA spectra. The localized PBI triplet (³PBI*) exhibits unusually long lifetimes (up to 272 μs) as determined by the TTET experiment. No long-lived charge-separated (CS) state was observed. While a Förster resonance energy transfer (FRET) probably occurs between PBI and the open-ring rhodamine, a photo-induced electron transfer is proposed to be responsible for the quenching of the fluorescence of the PBI moiety.

Novel cyclometalated Ir( iii ) complexes, with conjugated chromophores, show promising photosensitising capabilities in normoxic and hypoxic cell environments.

A set of push–pull donor substituted nitro‐perylenediimide (NO ₂ ‐PDI)‐based derivatives NPDI 1 – 4 were designed and synthesized via nitration reaction of the mono‐brominated‐PDI (Br‐PDI) followed by Pd(II)‐catalyzed Sonogashira cross–coupling reaction in good yields. The nitro group was substituted at the bay position of the PDI‐NO ₂ , and a variety of donors (phenothiazine (PTZ), carbazole(CBZ), and N,N ‐dimethylaniline(NND) were functionalized on the other bay side. The photophysical, electrochemical, spectroelectrochemical, computational calculations, and nanosecond transient absorption (ns‐TA) studies were performed on the synthesized derivatives NPDI 1 – 4 . The photophysical properties of NPDI 2 – 4 exhibit absorption in the NIR region due to strong push–pull interaction, resulting in stabilized LUMO energy levels to a greater extent. The electrochemical study reveals that the redox potentials of NPDI 1 – 4 derivatives shifted toward the anodic side due to the strong electron‐withdrawing nature of the NO ₂ ‐PDI moiety. The spectroelectrochemical analysis revealed the absorption spectra shifted toward the bathochromic region during the reduction cycles, while a hypochromic shift occurred during the oxidation cycles. Nanosecond transient absorption spectral studies show that for the compounds containing strong electron donors (such as PTZ), either a short triplet state lifetime ( τ _T = 0.47 µs for NPDI2 ) or no ISC was observed ( NPDI4 ). For the compounds with moderate or no electron donor attached in the molecular structure, long triplet state lifetimes were observed ( τ _T = 86.9 µs for NPDI1 and τ _T = 47.8 µs for NPDI3 ). For the compounds lacking ISC ability, an intermolecular triplet photosensitizing method, and long triplet state lifetimes were observed ( τ _T = 46 µs for NPDI4 ).