New Shoot from Old Tree—Harnessing Mighty FRET to Create Stimuli-Responsive RTP
2020; Elsevier BV; Volume: 3; Issue: 2 Linguagem: Inglês
10.1016/j.matt.2020.07.023
ISSN2590-2393
Autores Tópico(s)Molecular Sensors and Ion Detection
ResumoAchieving stimulus-responsive room-temperature phosphorescence (RTP) materials with high practicality in a facile manner remains challenging. In this issue of Matter, Yang, Tang, Li et al. harnessed the mighty distance-sensitive Förster resonance energy transfer strategy to generate a highly efficient stimuli-responsive RTP system. Moreover, synchronous thermal printing and information encryption was unprecedentedly realized with the developed FRET-based RTP material. Achieving stimulus-responsive room-temperature phosphorescence (RTP) materials with high practicality in a facile manner remains challenging. In this issue of Matter, Yang, Tang, Li et al. harnessed the mighty distance-sensitive Förster resonance energy transfer strategy to generate a highly efficient stimuli-responsive RTP system. Moreover, synchronous thermal printing and information encryption was unprecedentedly realized with the developed FRET-based RTP material. Photoluminescent materials have exerted crucial impacts on people's daily lives. Among the light-emitting materials, persistent room-temperature phosphorescence (RTP) materials with lifetimes longer than 0.1 s are fascinating, with exceptional applications in newly emerged technologies including anti-counterfeiting, information recording, display and lighting, chemosensing, biological imaging, and so on.1Kabe R. Adachi C. Organic long persistent luminescence.Nature. 2017; 550: 384-387Crossref PubMed Scopus (162) Google Scholar Organic persistent RTP materials have gained significant breakthroughs in lifetime-tuning thanks to their structural diversity. Nevertheless, as a result of the normally low phosphorescence efficiency of organic materials in comparison with their well-developed inorganic counterparts, developing organic persistent RTP remains an urgent but lagging issue. Thankfully, in the past decade, ingenious molecular design and precise preparation approaches were taken advantage of, and a series of high-performance organic RTP systems have been engineered on the basis of comprehensive understanding and manipulation of the phosphorescence mechanism.2Ma X. Wang J. Tian H. Assembling-Induced Emission: An Efficient Approach for Amorphous Metal-Free Organic Emitting Materials with Room-Temperature Phosphorescence.Acc. Chem. Res. 2019; 52: 738-748Crossref Scopus (201) Google Scholar The H-aggregation,3An Z. Zheng C. Tao Y. Chen R. Shi H. Chen T. Wang Z. Li H. Deng R. Liu X. Huang W. Stabilizing triplet excited states for ultralong organic phosphorescence.Nat. Mater. 2015; 14: 685-690Crossref PubMed Scopus (778) Google Scholar halogen bonding,4Cai S. Shi H. Tian D. Ma H. Cheng Z. Wu Q. Gu M. Huang L. An Z. Peng Q. et al.Enhancing ultralong organic phosphorescence by effective π-type halogen bonding.Adv. Funct. Mater. 2018; 28: 1705045Crossref Scopus (142) Google Scholar and n–π transition5Zhao W. He Z. Lam J.W.Y. Peng Q. Ma H. Shuai Z. Bai G. Hao J. Tang B.Z. Rational molecular design for achieving persistent and efficient pure organic room-temperature phosphorescence.Chem. 2016; 1: 592-602Abstract Full Text Full Text PDF Scopus (311) Google Scholar have been employed as design principles, and co-crystallization,6Bolton O. Lee K. Kim H.-J. Lin K.Y. Kim J. Activating efficient phosphorescence from purely organic materials by crystal design.Nat. Chem. 2011; 3: 205-210Crossref PubMed Scopus (782) Google Scholar,7Gu L. Shi H.F. Bian L.F. Gu M.X. Ling K. Wang X. Ma H.L. Cai S.Z. Ning W.H. Fu L.S. et al.Colour-tunable ultra-long organic phosphorescence of a single-component molecular crystal.Nat. Photonics. 2019; 13: 406-411Crossref Scopus (211) Google Scholar host–guest interaction,8Li D. Lu F. Wang J. Hu W. Cao X.M. Ma X. Tian H. Amorphous metal-free room-temperature phosphorescent small molecules with multicolor photoluminescence via a host-guest and dual-emission strategy.J. Am. Chem. Soc. 2018; 140: 1916-1923Crossref Scopus (240) Google Scholar and doping luminophore in rigid matrix9Lee D. Bolton O. Kim B.C. Youk J.H. Takayama S. Kim J. Room temperature phosphorescence of metal-free organic materials in amorphous polymer matrices.J. Am. Chem. Soc. 2013; 135: 6325-6329Crossref Scopus (254) Google Scholar,10Kwon M.S. Lee D. Seo S. Jung J. Kim J. Tailoring intermolecular interactions for efficient room-temperature phosphorescence from purely organic materials in amorphous polymer matrices.Angew. Chem. Int. Ed. Engl. 2014; 53: 11177-11181Crossref Scopus (223) Google Scholar have been utilized as enhancing strategies to effectively realize enhanced organic RTP. However, persistent organic RTP materials sensitive to external stimulus are still very rare, especially the practicably usable ones, because of the lack of efficient design strategy and the reliance on crystal engineering. Developing efficient RTP materials without the need for crystal engineering or a complex fabrication process is highly desirable. More importantly, establishing effective and universal methodology to achieve stimulus-responsive RTP in simple and easily available organic systems is of both fundamental and practical significance. Förster resonance energy transfer (FRET) strategy where the donor and acceptor are close to each other (∼1–10 nm) is an energy-transfer photophysical process that is strongly dependent on the distance. The FRET efficiency is inversely proportional to the six power of the donor-to-acceptor distance (R–6). The first definition of FRET as a "spectroscopic ruler" for distance measuring in 1967 by Stryer and Haugland initiated a new era with the application of FRET rulers to investigate a broad range of scientific problems.11Stryer L. Haugland R.P. Energy transfer: a spectroscopic ruler.Proc. Natl. Acad. Sci. USA. 1967; 58: 719-726Crossref PubMed Scopus (1495) Google Scholar Given its unique optical properties and intrinsic distance-sensitive specificity, FRET coupling luminescent donor and energy acceptor nowadays still functions as a powerful spectroscopic technique that has been extensively used for all applications of luminescence including the analysis of a large variety of substances and events. Despite this, the FRET process has seldomly been applied to construct organic persistent RTP materials, not to mention the ones with good stimulus-responsive capability. In this issue of Matter, Yang, Tang, Li et al.12Wang Y. Yang J. Fang M. Yu Y. Zou B. Wang L. Tian Y. Cheng J. Tang B.Z. Li Z. Förster Resonance Energy Transfer: An Efficient Way to Develop Stimulus-Responsive Room-Temperature Phosphorescence Materials and Their Applications.Matter. 2020; 3 (this issue): 449-463Abstract Full Text Full Text PDF Scopus (50) Google Scholar report the smart utilization of the distance-sensitive "old" FRET process in a host-guest doping system to accomplish "novel" persistent RTP that could be turned on by heating or mechanical force. By means of an array of rational experiments and theoretical calculation, deep insight on the relationship between the stimulus-responsive RTP effect and the FRET process including the role of the donor-acceptor interaction was gained. Moreover, benefiting from the unique force/heating-responsive RTP effect, the developed RTP material was successfully and unprecedently employed in synchronous thermal printing and information encryption. Specifically, N,N-Dimethylpyridin-4-amine (DMAP), where the formation of intermolecular H-bonds could be facilitated by its multiple nitrogen atoms, was selected as the host and FRET donor, while di-(naphthalen-2-yl)-amine (Cdp) whose derivatives were reported to show RTP emissions under the rigid environments was chosen as the guest and FRET acceptor. Wherein, the host DMAP provides rigid environment, the guest Cdp enjoys efficient singlet-to-triplet intersystem crossing (ISC) capability, and the energy levels between DMAP and Cdp are matched enough to conduct the FRET process. It means that the main criteria to achieve stimulus-responsive RTP effect in a host-guest system on the basis of FRET are fully satisfied. As a result, when stimulated by force or heat, the originally separated DMAP and Cdp would be pushed close to each other and gradually coalesce with the decreasing molecular distance, subsequently displaying superior RTP performance in air (Figures 1A and 1B ). When the DMAP and Cdp were physically mixed together in a mass ratio of 100:1, the mixture merely exhibited the donor emission (λem = 334 nm). Upon grinding, the fluorescence of the acceptor peaked at 405 nm was gradually intensified with the gradual decrease in the donor emission, indicating the occurrence of the FRET process. The FRET efficiency was enhanced as the grinding proceeded. When ground for 30 s, the FRET efficiency was 39.77%, boosted to 48.99% at 60 s, and arrived at the maximum of 66.86% at 120 s. Meanwhile, persistent RTP was able to be evidently recorded with the phosphorescence ranging from 500 to 600 nm, which is consistent with the phosphorescence of Cdp at 77 K. It demonstrated that the RTP emission was switched on by grinding and was originated from Cdp as well as the restriction of molecular motions from DMAP. Similarly, high-contrast RTP emission could also be triggered by heating. Particularly, the visual afterglow from Cdp got longer as the temperature rose and exceeded 4 s after thermal treatment at 110°C for 10 min, when the FRET efficiency reached 54.47% and the RTP efficiency and lifetime was up to 3.16% and 756 ms, respectively. These results suggested that grinding and heating the energy donor and luminescent acceptor together were indeed effective approaches to obtain the FRET system as well as the subsequent RTP effect. Making full use of the specific recognizing ability between the FRET donor and the acceptor, the synchronous thermal printing and information encryption was accomplished with the developed stimulus-responsive RTP material. More specifically, as depicted in Figure 1C, the thermal papers separately dip-coated with DMAP (layer A) and Cdp (layer B) on one side were stacked together. When passed over the print head, spots of Cdp would approach DMAP after penetrating layer A under the synergistic actions of heating and pressure, making a persistent RTP emission emerge with a set pattern. The afterglow of a preset 2D code could be observable by the naked eye and the encrypted information was able to be identified by mobile phone after turning off the UV irradiation. Given its excellent heating- and force-responsive RTP effect, up to four layers of thermal-pressure-sensitive replication was also easily achieved. The information printed on a matrix using DMAP as a pigment initially could not be seen by the naked eye because of the emission lying in the UV region. Whereas, when sprayed with Cdp solution, the printed information emitted bright phosphorescence to make the information precisely identified by the naked eyes after stopping the UV irradiation. Hence, multiple information encryptions were realized by taking advantage of the specificity of the donor-acceptor FRET pairs. The wide adaptability of FRET to various environments, superb RTP properties of the host-guest system, and the low cost and commercial availability of the host and guest collaboratively guarantee the practicability of the resulted stimulus-responsive RTP materials. The FRET-based stimulus-responsive RTP construction strategy presented herein is facile, highly efficient, and undoubtedly commercially viable and exempt of sophisticated molecular design and synthesis as well as complicated fabrication procedure such as crystal engineering. It is worth noting that the FRET-based stimulus-responsive RTP system definitely should not be limited to the DMAP-Cdp system. In principle, any system that meets the following main requirements would exhibit FRET-based stimulus-responsive RTP effect: (1) a host that could offer rigid environment, (2) a guest that possesses satisfactory singlet-to-triplet ISC capability to generate RTP emission, and (3) the well-matched host and guest energy levels that, on one hand, ensure sufficient spectral overlap between the host emission and the guest absorption and, on the other hand, make the highest occupied and lowest unoccupied molecular orbitals of the guest molecule completely wrapped by the host's. Thus, the present creative work not only provided a highly practically applicable RTP material but also established a new platform for the future development of purely organic stimulus-responsive RTP materials. Furthermore, the work also offered insightful knowledge in efficient methodology for the rational design of stimulus-responsive RTP materials in the future. Despite this, the RTP emission of this FRET host-guest system still lies in the yellowish green-light region. Therefore, to promote the application of FRET-based stimulus-responsive RTP in the biological area, RTP materials with emission in the red/near-infrared light range should be explored. It might be one direction of future research in the RTP area. We thank the NSFC /China ( 21788102 , 21875064 , 21604023 , and 21790361 ), the Shanghai Municipal Science and Technology Major Project ( 2018SHZDZX03 ), the Programme of Introducing Talents of Discipline to Universities ( B16017 ), Shanghai Science and Technology Committee ( 17520750100 ), the Shanghai Sailing Program ( 16YF1402200 ), and the Fundamental Research Funds for the Central Universities for financial support. Förster Resonance Energy Transfer: An Efficient Way to Develop Stimulus-Responsive Room-Temperature Phosphorescence Materials and Their ApplicationsWang et al.MatterJune 3, 2020In BriefFörster resonance energy transfer, a typical distance-sensitive energy-transfer process, was utilized to develop stimulus-responsive RTP material. With unique force and heating-responsive RTP effects, this material was successfully applied in synchronous thermal printing and information encryption for the first time. Full-Text PDF Open Archive
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