Effect of π···π Interactions of Donor Rings on Persistent Room-Temperature Phosphorescence in D₄–A Conjugates and Data Security Application

Abstract

Organic room-temperature phosphorescence (RTP) materials with persistent RTP (PRTP) have attracted huge interest in inks, bioimaging, and photodynamic therapy. However, the design principle to increase the lifetime of organic molecules is underdeveloped. Herein, we show donor(D 4 )−acceptor(A) molecules (TOEPh, TOCPh, TOMPh, TOF and TOPh) with similar orientation of donor rings in aggregates that cause a large number of noncovalent interactions. We observed that TOEPh, TOCPh, TOMPh and TOF showed PRTP, whereas TOPh showed only phosphorescence emission (Φ P = ∼11%) with no PRTP property at ambient conditions. The spectroscopic and single-crystal X-ray analyses confirm the molecular assembly via J-aggregation with a face-to-face orientation of the donor rings. The crystal structure analysis (TOEPh, TOCPh, TOMPh, TOF) reveals that moderate π•••π interactions (3.706 to 4.065 Å) between the donor rings cause the enhancement of the phosphorescence lifetime (26 to 245 ms), whereas the short phosphorescence lifetime (12 ms) of TOPh was observed because of the absence of π•••π interactions. We found that TOEPh shows a long lifetime (245 ms) as compared to other derivatives because of the presence of ethoxy (−OEt) groups that enables spin−orbit coupling caused by strong lone pair (O)•••π interactions present in the molecule. Utilizing the PRTP feature of TOEPh and the fluorescence emission of TOPh, we have shown data security applications in poly(methyl methacrylate).

Thermally Activated Delayed Fluorescence and Room-Temperature Phosphorescence in Asymmetric Phenoxazine-Quinoline (D2–A) Conjugates and Dual Electroluminescence

“…However, designing such emitters is an exasperating task. This is mainly because pure organic materials are intrinsically incapable of efficient phosphorescence under ambient conditions due to the spin-forbidden process, although several design strategies, for example, intramolecular and/or intermolecular interactions (lone pair···π, π···π, and hydrogen bonding), , aggregates, , host–guest, , deuteration, excited-state engineering, internal heavy chalcogen atom effect, and the presence of heavy elements in the molecular backbone, have been adopted. Nevertheless, a handful of reports have recently demonstrated on the simultaneous use of TADF and RTP from single molecular systems.…”

Molecular Uniting Set Identified Characteristic (MUSIC) of Organic Optoelectronic Material

“…According to Jablonski energy diagram of photoluminescence (Figure 1), [ 58 ] two essential factors are required for brilliant RTP emission: 1) efficient intersystem crossing (ISC) process from the lowest singlet excited state (S 1 ) to triplet excited states (T n ), 2) stable triplet excited states. Generally, two major structural characteristics are needed for pure organic RTP molecules, one is the conjugated skeleton with rigid structure as the core unit, [ 59‐60 ] another is the suitable substituent that can promote the efficient intermolecular interactions, and tune the molecular configurations and electronic properties. [ 61 ] In most cases, these two pieces work together to form the stable excited state by efficient electron coupling effect and rigid aggregated forms.…”

Ultralong phosphorescence cellulose with excellent anti-bacterial, water-resistant and ease-to-process performance

“…Compared with traditional metal-based phosphorescent materials, organic room-temperature phosphorescence (RTP) materials have low toxicity, low cost, and high flexibility. As a result, they have garnered tremendous interest in biomedical applications, information security, anticounterfeiting, flexible displays, comfortable wearable devices, photochemical catalysis, etc 5 – 19 .…”