Modelling aggregation-induced emission in organic crystals

Dr Rachel Crespo-Otero, Queen Mary University. Part of the Physical Seminar Series

Abstract: Light emitting materials find applications in display technologies, optical communication, data storage, biological sensing and solid-state lasing.

1. Aggregation-induced emission (AIE) offers a route for the development of luminescent technologies with high quantum efficiencies. Excited state intramolecular proton transfer (ESIPT) coupled with AIE can produce devices with emission across the visible spectrum. Recently, ESIPT-active solid-state emitters based on 2′-hydroxychalcone have been synthesized.
2. 2 The compounds are almost non-emissive in solution but depending on the nature of the substituent can emit in the deep red/NIR region when crystalline. To decipher the role of aggregation in the solid-state, we use a combination of static, non-adiabatic dynamics and solid-state simulations.
3. and 4. We identify two competing non-radiative relaxation channels, driven by intramolecular rotation in the enol and keto excited states. In the vacuum, both mechanisms are accessible for the five compounds studied. We analyse how inter- and intramolecular processes determine the emissive properties in the crystal environment, where the population of nonradiative pathways is dictated by the electronic effects of the substituents and the degree of distortion allowed in the crystal environment.

Localisation of the electron density is crucial to maximise fluorescence via ESIPT. This systematic investigation extends the current interpretation of AIE to polar chromophores with multiple decay pathways. Our conclusions offer design strategies for the development of luminescent molecular crystals.

References:

• J. Gierschner, S. Varghese and S. Y. Park, Adv. Opt. Mater., 2016, 4, 348–364.
• H. Zhang, X. Cheng, K. Wang, S. Huang, H. Zhang and Y. Wang, Angew. Chemie - Int. Ed., 2015, 54, 8369–8373.
• M. Dommett and R. Crespo-Otero, Phys. Chem. Chem. Phys., 2017, 19, 2409–2416.
• M. Dommett, M. Rivera and R. Crespo-Otero, J. Phys. Chem. Lett., 2017, 6148–6153.