Photo-thermo-induced room-temperature phosphorescence through solid-state molecular motion

Abstract

The development of smart-responsive materials, in particular those with non-invasive, rapid responsive phosphorescence, is highly desirable but has rarely been described. Herein, we designed and prepared a series of molecular rotors containing a triazine core and three bromobiphenyl units: o-Br-TRZ, m-Br-TRZ, and p-Br-TRZ. The bromine and triazine moieties serve as room temperature phosphorescence-active units, and the bromobiphenyl units serve as rotors to drive intramolecular rotation. When irradiated with strong ultraviolet photoirradiation, intramolecular rotations of o-Br-TRZ, m-Br-TRZ, and p-Br-TRZ increase, successively resulting in a photothermal effect via molecular motions. Impressively, the photothermal temperature attained by p-Br-TRZ is as high as 102 °C, and synchronously triggers its phosphorescence due to the ordered molecular arrangement after molecular motion. The thermal effect is expected to be important for triggering efficient phosphorescence, and the photon input for providing a precise and non-invasive stimulus. Such sequential photo-thermo-phosphorescence conversion is anticipated to unlock a new stimulus-responsive phosphorescence material without chemicals invasion.

Introduction

Room-temperature phosphorescence (RTP) is luminescence that originates from the radiative transition from excited triplet state to ground state. Traditional inorganic RTP materials, which typically require noble or rare earth metals, have some intrinsic problems, including high cost, potential toxicity, and instability in aqueous environments^1,2,3. It is thus essential to develop environmentally friendly, metal-free pure organic RTP materials^4,5. Quantum yield and lifetime are the two critical indices for evaluating the performance of RTP materials. Thanks to the enthusiasm of many scientists, pure organic RTP systems with strong emission and long afterglow have been developed using many different strategies, including crystal engineering^6,7,8,9, host-guest interactions¹⁰, H-aggregation^11,12,13, and polymer-matrix assistance¹⁴. Smart-responsive RTP materials, in which the RTP responds to external stimuli, have been described less often but are attracting increasing attention because of their widespread applications in sensing¹⁵, imaging^16,17,18, and anticounterfeiting

Data availability

All the data supporting the findings in this work are available within the manuscript and Supplementary information file. Source data are available for Figs. 2–5 in the associated source data file. Source data are provided with this paper.

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Acknowledgements

B.Z.T. gratefully acknowledges support from NSFC/China (21700102), Z.-Q.Y. thanks the support from NSFC/China (21875143) and Innovation Research Foundation of Shenzhen (JCYJ20180507182229597), Y.W. thanks the support from NSFC/China (21908146), W.Z. thanks the support from Shanghai Pujiang Program (20PJ1402900), Shanghai Science and Technology Commission Basic Project-Shanghai Natural Science Foundation (21ZR1418400). Z.H. thanks the support from Innovation Research Foundation of Shenzhen (GXWD20201230155427003-20200728150952003). Special thanks to the Instrumental Analysis Center of Shenzhen University (Lihu Campus).

Author information

1. These authors contributed equally: **ng Wang Liu, Weijun Zhao.

Authors and Affiliations

1. College of Chemistry and Environmental Engineering, Shenzhen University, Shenzhen, 518071, China

   **ng Wang Liu, Yue Wu, Zhengong Meng, **n Qi, Yiran Ren & Zhen-Qiang Yu

2. Feringa Nobel Prize Scientist Joint Research Center, School of Chemistry and Molecular Engineering, East China University of Science and Technology, Shanghai, 200237, China

   Weijun Zhao

3. School of Science, Harbin Institute of Technology, HIT Campus of University Town, Shenzhen, 518055, China

   Zikai He

4. School of Science and Engineering, Shenzhen Institute of Aggregate Science and Technology, The Chinese University of Hong Kong, Shenzhen, 518172, China

   Ben Zhong Tang

Contributions

Y.W., Z.-Q.Y., and B.Z.T. conceived the project and designed the experiments. X.W.L., W.Z., Y.W., X.Q., Y.R., and Z.-Q.Y. were primarily responsible for the data collection and analysis. X.W.L., W.Z., Y.W., Z.M., and Z.H. analyzed the RTP data. X.W.L., W.Z., and Y.W. prepared the figures and wrote the original manuscript text. Y.W., Z.-Q.Y., and B.Z.T. completed the manuscript. All the authors contributed to the discussions and manuscript preparation.

Corresponding authors

Correspondence to Yue Wu, Zhen-Qiang Yu or Ben Zhong Tang.

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Competing interests

The authors declare no competing interests.

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Nature Communications thanks Benedetta Carlotti and Manman Fang for their contribution to the peer review of this work. Peer reviewer reports are available.

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