Recently, The team of Academician Tian He and Professor Ma Jun of East China University of Science and Technology reported a series of one-component organic room temperature phosphorescent (N-BOX) materials that have achieved reversible changes between short-wavelength (blue) RTP and long-wavelength (yellow) RTP due to external stimulation (force, heat), molecules due to phase transition from crystalline to amorphous. Among them, in this series of one-component RTP materials, the phosphorescent quantum yield (Φp) is the highest 68.4%.
On May 16, 2022, the paper was published in Angew. Chem. Int. Ed. On.
Intelligent light-emitting materials with stimuli response can respond to external stimuli (e.g., light, heat, force, PH, etc.) to achieve changes in the luminous properties of the material. This property makes stimulus-responsive smart optical materials potentially useful in anti-counterfeiting, biological imaging, and optoelectronic devices. However, these materials are generally based on multi-component polymer systems, carbon dots, principal-object systems or doped systems, etc., and their luminescence is generally based on changes in fluorescence, such as changes from delayed fluorescence to phosphorescence or changes from phosphorescence to phosphorescence. Materials with room temperature phosphorescent (RTP) emission have a longer lifespan and greater Stokes displacement than fluorescent materials, giving them unique advantages in certain specific application scenarios and domains. Based on this, it is important to develop stimulus-responsive materials based on RTP changes in one-component systems, but it is extremely challenging to ensure the effective interfacular transfunction (ISC) rate of one-component materials in different states, so in recent years, one-component intelligent optical material systems based on RTP changes have been rarely reported.
In order to solve this problem, recently, the team of Academician Tian He and Professor Ma Jun of East China University of Science and Technology reported a series of one-component RTP materials (N-BOX) that can be reversed between efficient short-wavelength (blue) RTP and long-wavelength (yellow) RTP due to external stimuli (force, heat) due to phase transition. Among them, the phosphorescent quantum yield (Φp) of this series of one-component RTP materials is as high as 68.4 % (Figure 1).
Figure 1: Schematic diagram of the reversible change of N-BOX between efficient blue and yellow RTP due to phase transition under external stimuli
Since there are two aromatic carbonyl groups in the N-BOX molecule, the DFT and TD-DFT can further demonstrate this by compensating for the change in angular momentum during interfacline channeling by n→π* transitions (Figure 2). As the alkoxy chains in the N-BOX crystal molecule grow, the two aromatic carbonyl groups in the crystal molecule gradually transition from relative planarization to a vertical twisted structure, resulting in a change in the RTP emission wavelength of the N-BOX crystal (Figure 3).
Figure 2: Energy level plot and SOC coefficient calculated based on the 11-BOX monocrystalline structure
Figure 3: The optical system of two aromatic carbonyl groups in an N-BOX crystal with their RTP emission wavelengths
The crystal accumulation strength of N-BOX gradually decreases with the growth of alkoxy chains in crystal molecules, resulting in the crystal structure of N-BOX molecules being destroyed to amorphous state after grinding or thermal annealing (TA), thereby realizing the transition of N-BOX from blue RTP to yellow RTP before and after grinding or before and after TA (Figure 4). After grinding or TA, N-BOX will change from amorphous to crystalline after dichloromethane fumigation or heating to 50 °C, thereby realizing the reversible regulation of N-BOX luminescence (Figure 5).
Figure 4: Changes in the physical properties of light before and after grinding of 11-BOX crystal molecules and before and after TA
Figure 5: Changes in photophysical properties of the 11-BOX after grinding to recover to the crystalline state by heating to 50 °C
N-BOX molecules have low melting and freezing points, and can achieve reversible change between crystalline and amorphous states, making them have good application prospects in the field of thermal response encryption and multicolor encryption (Figure 6).
Figure 6: 11-BOX application on thermal encryption and multi-color encryption
Taken together, the paper reports a series of highly efficient RTP materials based on one-component systems with multi-stage stimulus responsiveness. It provides a new idea for the subsequent design of highly efficient RTP materials with one-component and multi-stage stimulus response. (Source: Science Network)
Related paper information:https://doi.org/10.1002/anie.202206157