Feng Li

Triplet‐associated recombination remains a potential loss channel in high‐efficiency nonfullerene organic solar cells, particularly when separated charges re‐encounter to form spin‐correlated charge‐transfer or polaron‐pair states. Here, we introduce the air‐stable organic radical TTM‐1Cz as an additive to manipulate the triplet formation by the single electron–occupied doublet state characteristic of radicals. Electron paramagnetic resonance measurements confirm that the radical character of TTM‐1Cz is retained after solution processing. Grazing‐incidence wide‐angle x‐ray scattering measurements show that TTM‐1Cz and its structurally related closed‐shell analogue α HTTM‐1Cz induce comparable, modest increases in crystalline coherence, indicating a structural contribution associated with the common molecular framework. In contrast, charge‐separated‐state‐normalized transient absorption spectroscopy reveals a pronounced reduction in the late‐time triplet‐associated signal only in the TTM‐1Cz‐containing blend. Together with magneto‐photocurrent measurements and local molecular‐complex calculations, these observations are consistent with an additional, radical‐specific perturbation of spin‐dependent charge‐transfer recombination. The optimized D18:L8‐BO:TTM‐1Cz device achieves a champion power conversion efficiency of 20.63%, with a certified efficiency of 20.45%. These results reveal a design principle for radical additives in organic solar cells, in which molecular‐packing effects and spin‐active modulation of recombination act as distinct but complementary contributions.

Diradical compounds provide an intriguing platform for investigating multicenter bonding and the effects of electronic coupling.

Photochemical upconversion by annihilation of two triplet excitons to a higher-energy singlet state enables energy control of photons in optoelectronics and photonics. Upconversion initiated by a closed-shell sensitizer is limited by energy losses from singlet–triplet intersystem crossing. Here we explore open-shell organic radicals as sensitizers and their closed-shell hydrogenated analogues as annihilators in photon upconversion. The sensitizer combines optical transitions from a triphenylmethyl (TTM-1Cz) radical with energy-degenerate triplet states of an anthracene-based component (DPA) in one molecule (TTM-1Cz-DPA). The difference of one hydrogen atom in its closed-shell counterpart (HTTM-1Cz-DPA) switches the spin-optical properties to an annihilator that can mediate efficient upconversion. Red-to-blue photon upconversion by intermolecular energy transfer, from open-shell sensitizer to closed-shell annihilator, is demonstrated in solution with an apparent anti-Stokes shift higher than 0.9 eV and 7% quantum efficiency. We evaluate this mechanism against true ‘single component’ mixtures for upconversion and find that the presence of hydrogenated precursor with radicals is essential for high performance. Understanding the emergent spin-optical properties from paired open-shell and closed-shell systems enables new opportunities for energy management from the same molecular frame.

Organic radicals offer unique optoelectronic properties beyond those of conventional closed-shell materials, making them attractive candidates for advanced biomedical applications. However, their practical use is severely hindered by the intrinsic instability, and effective generation of ultrasound-responsive reactive oxygen species (ROS) with hypoxia tolerance remains largely unexplored. Here, we report a highly stable open-shell radical-based immunogenic sono/photodynamic theranostic system that enables second near-infrared (NIR-II) bioimaging and efficient tumor eradication under both light and ultrasound excitation. By employing a symmetric dual-acceptor molecular design, we develop a donor–acceptor radical (NTM-2) that exhibits a 13-fold enhancement in photodegradation resistance relative to that of the pristine radical. Upon 808 nm irradiation, NTM-2 nanoparticles simultaneously display bright NIR-II emission, pronounced photothermal conversion, and efficient type-I ROS generation. In vivo studies demonstrate high-resolution NIR-II vascular imaging and near-complete tumor ablation under photoactivation. Notably, under ultrasound stimulation, NTM-2 nanoparticles generate type-I ROS efficiently, leading to potent sonodynamic tumor suppression and significantly prolonged survival in tumor-bearing mice. This work establishes a molecular strategy for stabilizing organic radicals and highlights their potential as robust open-shell emitters for hypoxia-tolerant immunogenic sono/photodynamic cancer theranostics.

Excitons in organic materials are emerging as an attractive platform for tunable quantum technologies. Structures with near-degenerate doublet and triplet excitations in linked trityl radical, acene and carbazole units can host quartet states. These high spin states can be coherently manipulated, and later decay radiatively via the radical doublet transition. However, this requires controlling the deexcitation pathways of all metastable states. Here we establish design rules for efficient quartet generation and recycling to luminescence, using different connection arrangements of the molecular units. We discover that electronic coupling strength between these units dictates quartet formation and delayed emission yields, particularly through a Coulombically tuned acene-radical charge transfer state. This state acts as a source of non-radiative decay when acene-radical separation is small, but facilitates reversible doublet-quartet interconversion when acene-radical separation is large. Using these rules we report a material with 55% luminescence yield, where 94% of emitting excitons are recycled from the quartet with a 1.0 μ s lifetime. This reveals the central role of molecular topology in luminescent quantum materials.

Organic luminescent radicals with efficient doublet emission can directly transfer electrons and energy to oxygen, enabling fluorescence‐guided photodynamic therapy. However, their water insolubility and unclear oxygen interaction mechanisms limit their application. To address these challenges, we synthesized an amphiphilic organic radical (TTM‐2PyPh) that forms self‐assembled water‐soluble nanoparticles (TTM‐2PyPh_SA@NPs) with deep‐red emission, serving as Type‐I/II photosensitizers. Quantum chemistry calculations confirm an efficient electron transfer process between the radicals and oxygen. These nanoparticles self‐assemble in vivo, target tumors, and produce reactive oxygen species more effectively than core‐shell nanoparticles (TTM‐2Py_CS@NPs), chlorin e6, and methylene blue. Additionally, TTM‐2PyPh_SA@NPs demonstrate superior tumor eradication in vivo. This work advances the development of novel water‐soluble radical‐based photosensitizers for enhanced photodynamic therapy.

Developing purely organic emitters capable of delivering efficient electroluminescence beyond 800 nm remains a central challenge due to severe non‐radiative losses governed by the energy‐gap law and strong exciton–vibration coupling. Herein, we report a molecularly engineered luminescent radical, TTM‐DPS, synthesized by incorporating N,N‐diphenylthiophen‐2‐amine (DPS) into the tris(2,4,6‐trichlorophenyl)methyl (TTM) radical. This donor‐acceptor arrangement enhances long‐range charge‐transfer coupling while preserving a non‐bonding hole‐electron distribution in the D ₁ doublet state, effectively suppressing high‐frequency vibrational modes that typically trigger non‐radiative decay. As a result, TTM‐DPS exhibits deep‐NIR photoluminescence with a peak at 895 nm and a fourfold enhanced quantum yield (4%) relative to the fused donor analogue TTM‐2PTI (2PTI, 4‐phenyl‐4H‐thieno[3,2‐b]indole). When incorporated into OLEDs, TTM‐DPS enables deep‐NIR emission at 883–908 nm, achieving an external quantum efficiency of 1.26% and a radiance of 25800 mW sr ⁻¹ m ⁻² , ranking among the best metal‐free emitters operating in this spectral region. This work establishes a generalizable donor‐engineering strategy to mitigate exciton‐vibration coupling in radical systems, offering a promising pathway toward next‐generation high‐efficiency deep‐NIR optoelectronics.

Donor–acceptor type near-infrared luminescent radicals were synthesized in high yields via an iodinated building block.

Triphenylmethyl (trityl) radicals have shown potential for use in organic optoelectronic and spintronic applications. However, due to the poor luminescence of alternant symmetry hydrocarbons, the design of practical trityl structures has been limited to donor-radical intramolecular charge-transfer systems to break the alternant symmetry, which results in poor emission and photostability in polar solvents. Here, we synthesized a series of donor-acceptor (D-A^•) neutral radicals based on the tris(2,4,6-trichlorophenyl)methyl (TTM) radical moiety by introducing the 9H-tribenzo[b,d,f]azepine (TBA) ring with 20 π electrons as a donor group. In contrast to other TTM-based D-A^• radicals, these TBA radicals exhibit unique and superior properties for luminescent efficiency (56% in acetonitrile) and photostability (t_1/2= 4.3 × 10⁵ s, with estimated half-lives reaching up to several days) in polar solvents. Transient absorption (TA) spectra reveal the occurrence of an efficient transformation from the Franck-Condon (FC) state to the zwitterionic resonance intramolecular charge-transfer (ICT) state with a time constant of a few picoseconds. Due to the zwitterionic resonance ICT character, nonradiative decay channels, which are dominated by high-frequency modes (over 1000 cm^-1) in TBA radicals, can be efficiently suppressed. The present study highlights the promotion of antiaromaticity relief in luminescent radicals and offers a valuable viewpoint for understanding the ICT excited-state dynamics of D-A-type dyads in polar solvents.

Methamphetamine (MA), a highly potent synthetic illicit drug, poses grave threats to the global public health and societal stability. However, on-site fluorescence detection to MA (particularly those operating in the visible range─remain scarce). In this work, a boron-based ratiometric fluorescent probe, BA-FO-BA, synthesized by covalently conjugating a triarylborane derivative with fluorene is presented. Upon exposure to methylphenethylamine (MPEA, an MA simulant), the probe exhibits a 70 nm blue shift, significant fluorescence enhancement, and rapid and reversible response, accompanied by a distinct visible emission color change from blue to deep purple. This response is also validated using confiscated MA samples. Moreover, a sensing mechanism driven by B-N coordination-induced enhancement of the intramolecular locally excited (LE) state is proposed and substantiated. Therefore, this study not only introduces a novel molecular design strategy for amine detection characterized by a rare blue-shift response but also provides a new pathway for developing the ratiometric fluorescent probe featured LE properties.