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Aggregation-Induced Emission: From Small Molecules to Polymers—Historical Background, Mechanisms and Photophysics

Abstract

The enhancement of photoluminescence through formation of molecular aggregates in organic oligomers and conjugated organic polymers is reviewed. A historical contextualization of aggregation-induced emission (AIE) phenomena is presented. This includes the loose bolt or free rotor effect and J-aggregation phenomena, and discusses their characteristic features, including structures and mechanisms. The basis of both effects is examined in key molecules, with a particular emphasis on the AIE effect occurring in conjugated organic polymers with a polythiophene (PT) skeleton with triphenylethylene (TPE) units. Rigidification of the excited state structure is one of the defining conditions required to obtain AIE, and thus, by changing from a flexible ground state to rigid (quinoidal-like) structures, oligo and PTs are among the most promising emerging molecules alongside with the more extensively used TPE derivatives. Molecular structures moving away from the domination of aggregation-caused quenching to AIE are presented. Future perspectives for the rational design of AIEgen structures are discussed.

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Adapted from reference [124], with permission from RSC, Copyright 2019

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Adapted from reference [125], with permission from Elsevier, Copyright 2020

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Adapted from Refs. [101] and [106], with permission from Wiley, Copyright 2020

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Adapted from reference [142] with permission from ACS, Copyright 2018

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Adapted from reference [142] with permission from ACS, Copyright 2018

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Adapted from reference [98] with permission from RSC, Copyright 2020

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Adapted from reference [98] with permission from RSC, Copyright 2020

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Adapted from reference [153], with permission from ACS, Copyright 2020

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Acknowledgements

The authors acknowledge financial support from Project “Hylight” (no. 031625) 02/SAICT/2017, PTDC/QUI-QFI/31625/2017, which is funded by the Portuguese Science Foundation (Fundação para Ciência e Tecnologia, FCT) and COMPETE Centro 2020. We also acknowledge funding by Fundo Europeu de Desenvolvimento Regional (FEDER) through COMPETE and project ROTEIRO/0152/2013. The Coimbra Chemistry Centre (CQC) is supported through projects UIDB/00313/2020 and UIDP/00313/2020, co-funded by FCT and COMPETE 2020.

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This article is part of the Topical Collection “Aggregation Induced Emission”; edited by Youhong Tang and Ben Zhong Tang.

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Rodrigues, A.C.B., Seixas de Melo, J.S. Aggregation-Induced Emission: From Small Molecules to Polymers—Historical Background, Mechanisms and Photophysics. Top Curr Chem (Z) 379, 15 (2021). https://doi.org/10.1007/s41061-021-00327-9

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Keywords

  • AIE
  • Organic conjugated polymers
  • Polythiophenes
  • J-aggregates
  • Fluorescence