Aggregation‐induced emission (AIE) is a beneficial strategy for generating highly effective solid‐state molecular luminescence without suffering losses in quantum yield. However, the majority of reported AIE‐active molecules exhibit only strong fluorescence, which is not ideal for electrical excitation in organic light‐emitting diodes (OLEDs). By introducing various substituent groups onto the biscarbazole compound, a series of molecular materials with aggregation‐induced phosphorescence (AIP) is designed, which exhibits two distinctly different phosphorescence bands and an absolute solid‐state room‐temperature phosphorescence quantum yield up to 64%. Taking advantage of the AIE feature, the AIP molecules are fabricated into OLEDs as a homogeneous light‐emitting layer, which allows for relatively small efficiency roll‐off and shows an external electroluminescence quantum yield of up to 5.8%, more than the theoretical limit for purely fluorescent OLED devices. The design showcases a promising strategy for the production of cost‐effective and highly efficient OLED technology.

Manipulation of long-lived triplet excitons in organic molecules is key to applications including nextgeneration optoelectronics, background-free bioimaging, information encryption, and photodynamic therapy. However, for organic room-temperature phosphorescence (RTP), which stems from triplet excitons, it is still difficult to simultaneously achieve efficiency and lifetime enhancement on account of weak spin-orbit coupling and rapid nonradiative transitions, especially in the red and near-infrared region. Herein, we report that a series of fluorescent naphthalimides-which did not originally show observable phosphorescence in solution, as aggregates, in polymer films, or in any other tested host material, including heavy-atom matrices at cryogenic temperatures-can now efficiently produce ultralong RTP (f = 0.17, t = 243 ms) in phthalimide hosts. Notably, red RTP (l RTP = 628 nm) is realized at a molar ratio of less than 10 parts per billion, demonstrating an unprecedentedly low guest-to-host ratio where efficient RTP can take place in molecular solids.

Aggregation-induced emission (AIE) has proven to be a viable strategy to achieve highly efficient room temperature phosphorescence (RTP) in bulk by restricting molecular motions. Here, we show that by utilizing triphenylamine (TPA) as an electronic donor that connects to an acceptor via an sp3 linker, six TPA-based AIE-active RTP luminophores were obtained. Distinct dual phosphorescence bands emitting from largely localized donor and acceptor triplet emitting states could be recorded at lowered temperatures; at room temperature, only a merged RTP band is present. Theoretical investigations reveal that the two temperature-dependent phosphorescence bands both originate from local/global minima from the lowest triplet excited state (T1). The reported molecular construct serves as an intermediary case between a fully conjugated donor-acceptor system and a donor/acceptor binary mix, which may provide important clues on the design and control of high-freedom molecular systems with complex excited-state dynamics.

Many aggregation-induced emission (AIE) systems exhibit broad and structureless luminescence emission spectra resembling the Gaussian distribution, which is likely due to kinetically locked molecular conformers in the condensed phase. To verify the hypothesis, a series of tetraphenylethene (TPE) derivatives are synthesized and characterized as aqueous nanoparticle suspensions. It is found that the unsubstituted TPE exhibits reduced fluorescence intensity accompanied by a blueshift of the emission maximum, after the temperature of the aqueous suspension is elevated and cooled to room temperature again. For a naphthalimide-substituted TPE compound, thermal treatment of the AIE aqueous suspension results in complete, irreversible aggregation-caused quenching (ACQ) of fluorescence, which can be restored by a redissolving-precipitation process of thermally treated aggregates. The phenomenon is ascribed as a relative population shift of a kinetic AIE (k-AIE) state to a thermodynamic AIE (t-AIE) or ACQ state, evidenced by differential scanning calorimetry, dynamic light scattering, and scanning electron microscopy. The phenomenon may be universal for many other AIE systems and could be explored as stimuli-responsive materials.

The ability to modulate luminescence is crucial for organic light-emitting molecules. However, the correlation between molecular structure and emission is not always obvious and systematic. Here, using a well-established empirical rule on electrophilic substitution involving directing groups in organic chemistry, we present a model system, where two luminophores are covalently linked to benzene ortho, meta, and para to each other, to demonstrate that the rule can also be useful in predicting the fluorescence and phosphorescence behaviors of these disubstituted benzene molecules. The benzene ring works as a “molecular wire” that transduces electron density when the two luminophores form ortho- and para-isomers, while little to no transduction can be noted for the meta-isomer, based on well-established organic chemistry. We anticipate that many more “textbook examples” of electronic directing in organic chemistry can be used for systematic modulation of molecular fluorescence and room-temperature phosphorescence.

An ew strategy was devisedf or estimating and screening pK a values among different carbon acids under ambient conditions by using the UV/Vis absorption spectrum of persistent radicalp airs (PRPs),w hich are generated from an N-substituted naphthalimide (NNI) derivative in the presenceo fv ariousc arbanions in organic solutions. The electron paramagnetic resonance (EPR) spectroscopy was used to examinet he presence of radicals. Unexpectedly,i tw as discoveredt hat the UV/Vis spectrum of PRPs revealsadistinct linear relationship between the PRP absorptiona nd the pK a value of ac orresponding carbon acid, whichi sl ikely due to the energyd ifferencea mong different RPRs. The finding may offer organic chemists an alternative reference to conduct carbanion-mediated reactions in variouso rganic solutions. Knowing the pK a value of ad eprotonatable carbon atom attached to af unctional group (CH x R y ,d efined as ac arbon acid, CA, where x > 0, y > 0, and Rr epresenting the functional group) is criticali no rganic chemistry since it foretells the reactivity and selectivity of reactions participated by the a-carbon. Over the past century,aplethora of experimental techniques, including potentiometry, [1, 2] spectrometry, [3-5] conductometry, [6, 7] electrophoresis, [8, 9] nuclear magnetic resonance (NMR), [10, 11] voltammetry, [12, 13] high-performance liquid chromatography (HPLC), [14, 15] fluorometry, [16-18] and more recently,t heoreticalc alculations, [19, 20] have been employed to measure or estimate the pK a values of organic compounds.A mongt hese techniques, the UV/Vis spectroscopy method, similar to pH indicators, is particularly favored due to its wide accessibility, high throughput,a nd easy operation for non-experts. In organic solvents, however,m easuring the pK a values of CAs can be very challenging, mainly due to the complicated

Manipulation of long-lived triplet excitons in organic molecules is key to applications including nextgeneration optoelectronics, background-free bioimaging, information encryption, and photodynamic therapy. However, for organic room-temperature phosphorescence (RTP), which stems from triplet excitons, it is still difficult to simultaneously achieve efficiency and lifetime enhancement on account of weak spin-orbit coupling and rapid nonradiative transitions, especially in the red and near-infrared region. Herein, we report that a series of fluorescent naphthalimides-which did not originally show observable phosphorescence in solution, as aggregates, in polymer films, or in any other tested host material, including heavy-atom matrices at cryogenic temperatures-can now efficiently produce ultralong RTP (f = 0.17, t = 243 ms) in phthalimide hosts. Notably, red RTP (l RTP = 628 nm) is realized at a molar ratio of less than 10 parts per billion, demonstrating an unprecedentedly low guest-to-host ratio where efficient RTP can take place in molecular solids.

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