Design of Anti-Hund Organic Emitters Based on Heptazine.

Hund's rule, which is powerful in governing the first excited states of closed-shell organic materials, can hardly be violated to get inverted singlet-triplet gap (INVEST) molecules with negative singlet-triplet energy gaps (Δ), although INVEST materials have shown extraordinary photophysical properties and promising device performance especially in light-emitting diodes. Here, we propose a facile strategy to construct emissive INVEST molecules by introducing different types of substituents to heptazine in various modes, which can effectively tune the Δ to be negative with the enlarged oscillator strength () for the high fluorescence rate of the heptazine derivatives. Systematic computational studies show that the double substitution of electron-donating units with another nonconjugated substituent in hybrid substitution mode is the most favorable way in achieving slightly negative Δ and large values; the conjugated substituent will compete with heptazine to make the molecule deviate from the INVEST feature.

Exciton Dissociation and Recombination Afford Narrowband Organic Afterglow Through Efficient FRET.

Organic afterglow with long-persistent luminescence (LPL) after photoexcitation is highly attractive, but the realization of narrowband afterglow with small full-width at half-maximum (FWHM) is a huge challenge since it is intrinsically contradictory to the triplet- and solid-state emission nature of organic afterglow. Here, narrow-band, long-lived, and full-color organic LPL is realized by isolating multi-resonant thermally activated delayed fluorescent (MR-TADF) fluorophores in a glassy steroid-type host through a facile melt-cooling treatment. Such prepared host becomes capable of exciton dissociation and recombination (EDR) upon photoirradiation for both long-lived fluorescence and phosphorescence; and, the efficient Förster resonance energy transfer (FRET) from the host to various MR-TADF emitters leads to high-performance LPL, exhibiting small FWHM of 33 nm, long persistent time over 10 s, and facile color-tuning in a wide range from deep-blue to orange (414-600 nm).

Silver-Catalyzed Radical Cascade Sulfonation/Cycloaddition for the Construction of Multifunctional Succimides Containing Separable /-Isomers.

A silver-catalyzed cascade cycloaddition of -1,6-enynes, affording multifunctional succimide frameworks initiated by the arylsulfonyl radical addition, has been developed. This process shows mild reaction conditions, excellent structural selectivity, and broad functional group tolerance. In addition, the /-isomers can be easily separated, which provides an efficient method for obtaining pure /-configuration products.