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Realizing multiple stimuli responsiveness in organic molecular systems is very important and highly desirable to broaden their potential applications in smart materials. Such stimuli responsive materials are usually required in nontrivial multistep synthesis. In the present research, a series of asymmetrical naphthalene diimide derivatives (NDIs), which display interesting multiple external stimuli responsiveness including ultrafast photochromism and chemical stimulation chromism, with the generations of organic radical anions and charge transfer, were obtained by simple synthetic process. Importantly, the multicolored functionality was ingeniously achieved by mixing commercially available materials (guest molecules) and the readily-made asymmetrical NDIs through mechanical grinding under solvent-free conditions. Noteworthy the charge transfer processes, strongly depending on the distinctive structures of NDIs molecules as well as the weak intermolecular interactions, can be induced by external stimuli (i. e. light, chemical, or grinding). Subsequently, significant stimuli responsiveness as well as multicolored properties were realized and the underlying weak interactions-assisted charge transfer mechanism was thoroughly unearthed. A series of asymmetrical naphthalene diimide derivatives (NDIs) display interesting multiple external stimuli responsiveness including ultrafast photochromism and chemical stimulation chromism, which result from the generations of organic radical anions and charge transfer. Moreover, this system shows mechanical grinding toning with certain organic molecules, which have potential applications in smart materials. [Display omitted] • Radical-doped asymmetrical NDIs possess significant photochromism, chemical stimuli chromism and mechanical grinding toning. • Weak interactions-assisted charge transfer enable the generation of organic radicals, leading to multiple stimuli chromism. • Involved solvent-free synthesis and charge transfer process play key role in green synthesis and electron transfer chemistry. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) emitters in the long wavelength region usually suffer from severe nonradiative decay according to the energy-gap law, and show relatively large energy split (ΔE ST) between the lowest singlet and triplet excited states which compromise efficient up-conversion. Here, we report three orange and red TADF emitters comprising 5, 10-disubstituted phenazine electron-donor and quinoxaline-derived electron-acceptors, which show excellent TADF properties and yield efficient organic light-emitting diodes (OLEDs). These symmetrical acceptor-donor-acceptor (A-D-A) type and rodlike molecules concurrently exhibit high photoluminescence quantum yields up to 85% and fast reverse intersystem crossing. Experimental and theoretical studies reveal that these excellent photophysical properties are attributed the synergistic effect of structural rigidity, steric hindrance and strength of the donor and acceptor units. Doped OLEDs based on these emitters achieved high maximum external electroluminescence quantum efficiencies up to 19.9%, and maximum luminance surpassing 31240 cd/m2. [Display omitted] • Highly efficient orange to red TADF emitters with high PLQYs (up to 85%) and short TADF lifetimes. • Tiny S 1 -T 1 energy splits and fast spin-flip due to rational molecular design and excited-state regulation. • High-performance OLED with EQE nearly 20%. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) materials with through-space charge transfer (TSCT) have recently attracted extensive attention. However, how to rationally design high-performance TSCT-TADF emitters with small ΔE ST , high photoluminescence quantum yields (PLQYs) and high stability remains challenging. Herein, two triptycene-derived TADF molecules bearing ortho-donor (D)-acceptor (A) conformations are designed and characterized. These emitters exhibit unique V-shaped face-to-face D-A alignments with significant intramolecular D-A interactions, which mediate TSCT between the D and A moieties in addition to the through-bond charge transfer (TBCT) and facilitate realizing small ΔE ST and high efficiencies. Meanwhile, the rigid 3D triptycene scaffold endows the emitters with excellent thermal stability and high film-formation quality. These TADF emitters exhibit small ΔE ST of 6.7 and 10.8 meV and high photoluminescence quantum yields of 0.80 and 0.40 in doped films, respectively. The doped OLEDs employing these emitters achieve high external quantum efficiencies up to 20.5%. [Display omitted] • 3D triptycene scaffold based TADF emitters with photoluminescent efficiency up to 80%. • V-shaped face-to-face D-A conformation for constructing through-space charge transfer (TSCT) pathway. • High performance OLED with EQE beyond 20%. [ABSTRACT FROM AUTHOR]