Achieving Colorful Ultralong Organic Room-Temperature Phosphorescence by Precise Modification of Nitrogen Atoms on Phosphorescence Units

Huiwen Jin; Xue Zhang; Jiaxin Ma; Lijuan Bu; Chen Qian; Zewei Li; Yan Guan; Mingxing Chen; Zhimin Ma; Zhiyong Ma

doi:10.1021/acsami.3c14054

Achieving Colorful Ultralong Organic Room-Temperature Phosphorescence by Precise Modification of Nitrogen Atoms on Phosphorescence Units

ACS Appl Mater Interfaces. 2023 Nov 29;15(47):54732-54742. doi: 10.1021/acsami.3c14054. Epub 2023 Nov 14.

Authors

Huiwen Jin¹, Xue Zhang¹, Jiaxin Ma¹, Lijuan Bu², Chen Qian¹, Zewei Li³, Yan Guan³, Mingxing Chen³, Zhimin Ma³, Zhiyong Ma¹

Affiliations

¹ State Key Laboratory of Organic-Inorganic Composites, College of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, China.
² Chinese PLA Center for Disease Control and Prevention, Beijing 100071, China.
³ Beijing National Laboratory for Molecular Sciences, Key Laboratory of Polymer Chemistry and Physics of the Ministry of Education, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China.

PMID: 37964465
DOI: 10.1021/acsami.3c14054

Abstract

We successfully tune ultralong organic room-temperature phosphorescence (UORTP) by a simple strategy of precisely modifying nitrogen atoms on Phosphorescence Units, and colorful ultralong phosphorescence can be achieved. We for the first time investigate the structure-function relationship between phosphorescence properties and molecular structures of Phosphorescence Units. With BCz and BCz-1 as comparison, eight new Phosphorescence Units were synthesized by introducing one or two nitrogen atoms to the naphthalene moiety. For all the 10 Phosphorescence Units, their room-temperature ultralong phosphorescence in the PMMA film should be assigned to monomer phosphorescence from intrinsic T₁ decay. For Phosphorescence Units series I (BCz, NBCz-1, NBCz-2, NBCz-3, NBCz-4, NBCz-5, and NBCz-6), introducing one nitrogen atom to the naphthalene moiety can significantly affect the phosphorescence properties of Phosphorescence Units, and the effect is quite complicated. For modification on the inner ring, the T₁ energy level of NBCz-1 decreases, and the red shift of UORTP occurs while the T₁ energy level of NBCz-2 increases and the blue shift of UORTP happens. For modification on the outer ring, no phosphorescence color change is observed for NBCz-3 and NBCz-4, but their phosphorescence lifetimes vary notably due to different intersystem crossing efficiencies; as the modification site approaches the central five-member ring, the T₁ energy levels of NBCz-5 and NBCz-6 decrease, and their UORTP red shifts dramatically. For Phosphorescence Units series II (BCz, 2NBCz, BCz-1, and 2NBCz-1), introducing two nitrogen atoms to the outer six-member ring reduces energy level of T₁ excitons and leads to incredible red shift of UORTP for BCz and 2NBCz while surprisingly energy levels of T₁ excitons rise and UORTP blue shifts for BCz-1 and 2NBCz-1. Under the condition of proper modification sites, it is true that the more the additional nitrogen atoms, the more red-shifted the ultralong phosphorescence. This study may expand our knowledge of organic phosphorescence and lay the foundation for its future applications.

Keywords: Phosphorescence Unit; color tunability; introduction of nitrogen atom; monomer phosphorescence; ultralong organic room-temperature phosphorescence.