Halogen Bonding: A New Platform for Achieving Multi‐Stimuli‐Responsive Persistent Phosphorescence

Abstract

Monotonous luminescence has always been a major factor limiting the application of organic room‐temperature phosphorescence (RTP) materials. Enhancing and regulating the intermolecular interactions between the host and guest is an effective strategy to achieve excellent phosphorescence performance. In this study, intermolecular halogen bonding (CN⋅⋅⋅Br) was introduced into the host–guest RTP system. The interaction promoted intersystem crossing and stabilized the triplet excitons, thus helping to achieve strong phosphorescence emission. In addition, the weak intermolecular interaction of halogen bonding is sensitive to external stimuli such as heat, mechanical force, and X‐rays. Therefore, the triplet excitons were easily quenched and colorimetric multi‐stimuli responsive behaviors were realized, which greatly enriched the luminescence functionality of the RTP materials. This method provides a new platform for the future design of responsive RTP materials based on weak intermolecular interactions between the host and guest molecules.

Heavy-atom engineering of thermally activated delayed fluorophores for high-performance X-ray imaging scintillators

“…22 However, the photoluminescence quantum yield (PLQY) of organic phosphorescent materials is much lower than the fluorescence, and their phosphorescence is easily quenched by oxygen, which highly limits their radioluminescence (RL) efficiency. [23][24][25] Thermally activated delayed fluorescence (TADF) chromophores, in contrast, are some of the best candidates (if not the best) for high-performance scintillators due to their minimized singlet-triplet energy gap. This minimized gap allows such chromophores to harness both singlet and triplet excitons for light emission through highly efficient spin upconversion from triplet states to radiative singlet states, leading to unit exciton utilization efficiency (Figure 1a).…”

Halogen-bonded shape memory polymers

“…Second, the narrowly confined electropositive region along the R–X axis, known as the sigma-hole 10 , gives high directionality for XB, which has been utilized in supramolecular crystal engineering 11 and the design of halogen-bonded liquid crystals 12 , 13 . Third, the large size of the halogen atom taking part in the supramolecular interaction (frequently iodine or bromine) may act as a heavy-atom perturber in the context of light-emissive materials, thereby promoting phosphorescence emission in organic materials 14 , 15 . Finally, unlike HB, XB is hydrophobic by nature, enabling applications such as anion sensing and transport in an aqueous environment 16 – 18 .…”

Room‐temperature phosphorescence materials from crystalline to amorphous state

“…RTP, room temperature phosphorescence; TPA, terephthalic acid. Reproduced with permission: Copyright 2022, Wiley 33 …”

“…Introduction of chiral units in the organic phosphorescent co-crystals can also produce circularly polarized light emission. Duan's group 32 Smart-response RTP materials have widespread applications in phosphorescence switches, security papers, data storage, and so on, 33 because of the tunable luminescence triggered by external stimuli (mechanical force, temperature, pH, solvent polarity, etc.). Cai's group 33 proposed an effective strategy for RTP and multi-stimuli-responsive luminescence of a host-guest system through intermolecular halogen bonding.…”