Enhanced Emission under Mechanical Stimuli Based on Phenanthroimidazole Derivative by Controlling ISC Process

Abstract

In our previous work, we have reported an abnormal aggregation induced emission (AIE) material of t-Br-PhIm-Thi (M0) based on phenanthroimidazole (PI) derivative ( Figure S1, Supporting Information ). [7] Detailed examination revealed that the heavy atom effect contributes to the dark emission in dilute solution, while the bright emission upon aggregation in the longer wavelength mainly derived from the existence of abundant weak intermolecular interactions in the packing modes. On the other hand, cyanide styrene (CNS) has been widely involved in AIE and stimuli responsive material for its highly twisted conformation. [2a,3,8] Meanwhile, triphenylamine (TPA) is a well-known nonplanar and electron-rich molecular with large sizes. When TPA was introduced into CNS, its electronic donating essence would make a molecular with D-A structure favor for high luminescence efficiency while its large size would regulate intermolecular interactions such as π-π and CH … N, inducing different luminescent color or/and efficiency. [9] Taken all together, we designed and synthesized a new molecular denoted as Br-Thi-TPA-CN (M1) (Scheme S1, Supporting Information) by linking TPA with Br-Phim-Thi through CNS. As expected, the abundant interactions lead to different aggregates with different packing modes under varied conditions. Interestingly, some of the packing modes can be mutually transformed under external stimuli, accompanying with off-on luminescence by mechanical grinding which is reversible and easily discerned. Both the experiment and theory analysis revealed the regulation of intersystem crossing (ISC) process on change of packing modes in aggregates ascribes for this abnormal turn-on mechanochromic phenomenon. Limited works are reported about off-on type mechanochromic luminogens (MLs) owing to notorious quenching effect and lacking of reliable guidance.Here a novel strategy is proposed to develop off-on type ML based on phenanthroimidazole (PI) derivative by controlling the intersystem crossing (ISC) process through variation of packing mode. This work offers a molecular level understanding of the correlations between molecular structure, stacking modes, and photophysical properties. This is the first example of PI derivative for off-on ML based on controlling ISC process. Mechanochromic LuminogensOrganic luminogens with enhanced emission intensity in response to mechanical stimuli become particular appealing with abroad attention in sensors, data memories, and security ink applications, for it can not only provide a dual mode switch in a multifunction system but also avoid false positive signals for quenching effect of most interference after grinding. [1][2][3][4][5] However, while most reported works are concerned about the emission color switching, only limited mechanochromic luminogens (MLs) have been reported with intensity variation and most of them show decreasing emission efficiency, for the collapse of network constructed by intermolecular interactions would result in notorious aggregation induced quenching...

Mechanochromism and Aggregation-Induced Emission in Phenanthroimidazole Derivatives: Role of Positional Change of Different Donors in a Multichromophoric Assembly

“…Phenanthroimidazole (PI) has been extensively utilized to synthesize fluorescent materials for OLEDs, TADF, biomedical applications as well as for MFC. The PI core has a rigid aromatic framework with an imidazole ring fused to phenanthrene and possesses properties suitable for material applications such as high thermal and chemical stability, ambipolar nature, high fluorescence quantum yields, charge transporting ability, etc. − Herein, we have designed and synthesized six PI derivatives TPE-PI-1 , TPE-PI-2 , TPE-PI-3 , PTZ-PI-1 , PTZ-PI-2 , and PTZ-PI-3 by using a weak donor TPE (D) and a strong donor PTZ (D′) simultaneously. The mode of attachment of the donors and their position were also varied in these six derivatives, and its effect on their photophysical and electronic properties were studied.…”

Precise Regulation of Distance between Associated Pyrene Units and Control of Emission Energy and Kinetics in Solid State

“…[18][19][20][21][22][23] Thanks to the efforts of scientists, many ways have been found to change the structure of compounds to influence the packing modes of crystals so as to achieve different properties. [24][25][26][27][28][29] For instance, dimers, as one of the most important types in crystal packing, are always mentioned, and a great deal of research focuses on how to tune the π-π interactions in them. [30][31][32][33][34][35][36] Nevertheless, this research does not focus on controlling the distance of π-planes in dimers and precisely regulating the π-π interactions, while such results are likely to provide new insights on new molecular design with expected molecular packing in aggregates.…”