Solid-state photochromic materials are very attractive due to their promising future in advanced functional materials with reversible and tunable optical properties. However, the development of photochromic material in the solid...

Organic luminescent materials with the ability to reversibly switch the luminescence when subjected to external stimuli have attracted considerable interest in recent years. However, the examples of luminescent materials that exhibit multiresponsive properties are rarely reported. In this work, a new stimuli‐responsive dye P1 is designed and synthesized with two identical chromophores of naphthalimide, one at each side of an amidoamine‐based spacer. This amide‐rich molecule offers many possibilities for forming intra‐ and intermolecular hydrogen bond interactions. Particularly, P1 has an intrinsic property of cocrystallizing with methanol. Compared with the pristine P1 sample, the as‐prepared two‐component cocrystalline material displays an exceptive deep‐blue emission, which is extremely rare among naphthalimide‐based molecules in the solid state. Furthermore, the target material exhibits an obvious mechanochromic fluorescent behavior and a large spectral shift under force stimuli. On the other hand, the cocrystalline material shows an unusual “turn off” thermochromic luminescence accompanied by solvent evaporation. Moreover, using external stimuli to reversibly manipulate fluorescent quantum yields is rarely reported to date. The results demonstrate the feasibility of a new design strategy for solid‐state luminescence switching materials: the incorporation of solvents into organic compounds by cocrystallization to obtain a crystalline state luminescence system.

Organic room-temperature phosphorescence (RTP) materials have been paid great attention for their promising applications in anticounterfeiting, optical device, and bioimaging. However, owing to inefficient intersystem crossing (ISC), it still remains a challenge to develop organic RTP materials with both high quantum yields (Φ p ) and long lifetime (τ p ). Herein, a reasonable strategy is presented to modulate and balance the Φ p and τ p through the synergy effect of halogen bonding and heavyatom effect (HAE). Modulated RTP properties are successfully achieved by the introduction of halogen atoms into 4-(9-Hcarbazol-9-yl) benzonitrile due to enhanced ISC. Especially, CzBzBr shows the highest Φ p of 23.50% and CzBzCl exhibits the longest τ p of 607.4 ms. The excessive HAE of the bromine atom decreases the τ p of CzBzBr, while moderate HAE of the chlorine atom endows CzBzCl with both high Φ p and long τ p . In addition, the halogen bondings lead to specific halogen-mediated molecular cluster packing, further suppressing nonradiative transition for ultralong RTP emission. Through simple physical co-crystallization with adjusting the mass ratio of CzBzCl/CzBzBr, co-crystals with modulated RTP properties and white-light emission phenomena are obtained. Our study provides a rationale method to develop modulated high-efficiency RTP materials, which will expand their practical applications.

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A novel Rhodamine 6G-naphthalimide molecule is used for high-contrast fluorescence change upon acid and force stimuli in the solid state.