Employing Lactam Copolymerization Strategy to Effectively Achieve Pure Organic Room‐Temperature Phosphorescence in Amorphous State

Abstract

It is known that without noble metal, the spin flip between singlet states and triplet states is generally a forbidden process and that the long-lived triplet excitons of pure organic luminogens tend to undergo nonradiative decays including thermal motions, collision and exposure to quenchers such as oxygen. [6] Therefore, phosphorescence from metal-free materials is normally observed at low temperature (e.g., 77 K) and under inert conditions (e.g., protection by argon gas). [7] Tang and co-workers proposed crystallization-induced phosphorescence (CIP) mechanism, through which efficient RTP materials can be constructed. [8] Still, crystalline RTP materials require strict growth conditions, which might restrict their processability in applications.To overcome these shortcomings, several metal-free amorphous RTP materials have been reported. Methods of embedding pure organic phosphors into rigid polymer matrices, macro cycle hosts, or supramolecular hosts either covalently linked or noncovalently adsorbed are commonly used to inhibit nonradiative decay and enhance RTP emissions. [9] Amide phosphorescent polymers are frequently reported due to the rigid environment provided by both polymer matrices and hydrogen bonds. Our group has prepared several acrylamide copolymers, which are typical examples. [10] Nevertheless, the pure organic amorphous polymeric systems with effective RTP emission are still rare. Till now, amide copolymers with lactam structures bringing out RTP have rarely been reported, while poly(N-vinylpyrrolidone) (PVP) and poly(N-vinylcaprolactam) (PNVCL) are good candidates with facile preparations and wide availability of monomers.In this work shown in Scheme 1, a design strategy was presented for pure organic phosphorescent polymers (PVP-BrNpA, PVP-BA, PVP-BrHexene, PNVCL-BrNpA, PNVCL-BA and PNVCL-BrHexene) by copolymerizing lactam monomers, namely, N-vinylpyrrolidone (NVP) and N-vinylcaprolactam (NVCL) with small amounts of other monomers, benzonic acid (BA), bromonaphthalimide (BrNpA) and 6-Br-1-Hexene (BrHexene). Several PVP-and PNVCL-based copolymers emit notable RTP signals with diverse emission properties. The polymer matrices provide rigid environment for the phosphors, which restricts thermal motions and results in significant RTP emissions.PVP-BrNpA, PVP-BA, and PVP-BrHexene, which have five-membered lactam rings in their polymer chains, were Pure organic, amorphous room-temperature phosphorescent (RTP) materials have aroused great attention because of their easy preparation and wide applications. Herein, several metal-free, amorphous, lactam phosphorescent copolymers are prepared. Copolymers of N-vinylpyrrolidone (NVP) and N-vinylcaprolactam (NVCL) with small amounts of monomers exhibit diverse RTP emissions. The rigid polymer matrices of poly(N-vinylpyrrolidone) (PVP) and poly(N-vinylcaprolactam) (PNVCL) effectively help to inhibit nonradiative transition process of phosphors, which enhances the RTP emission. Furthermore, outstanding biocompatibility, low cost, and highly hydrophilic ch...

A facile way to obtain near-infrared room-temperature phosphorescent soft materials based on Bodipy dyes

“…[13][14][15][16][17][18] Amorphous polymers have been veried to be rigid enough to effectively suppress nonradiative transition and promote RTP emission. [19][20][21][22][23][24][25][26] Various phosphors with different conjugated structures have been utilized to obtain RTP emission of different colours, most of which are excited by UV light and exhibit RTP emission in the visible region. [27][28][29][30][31] Materials with absorption in the visible region and emission in the NIR region are promising candidates in a wide range of elds, such as medical and therapeutic applications, due to their high tissue penetration and low autouorescence.…”

Persistent Room‐Temperature Phosphorescence from Purely Organic Molecules and Multi‐Component Systems

“…designed several purely organic polymers (PVP–BrHexene, PNVCL–BrNpA, PVP–BrNpA, PVP–BA, PNVCL–BrHexene, and PNVCL–BA) based on lactams ( Figure a,b). [ 52 ] Except for PNVCL–BrHexene, the phosphorescence lifetimes (τ p ) of the polymers vary from 0.13 to 0.94 ms, with phosphorescence quantum yields (Φ p ) ranging from 0.4% to 1.6%. Lactam groups bearing lone pairs not only provide hydrogen bonds but also enhance the ISC rate.…”

Recent Advances of Polymer‐Based Pure Organic Room Temperature Phosphorescent Materials

“…In 2019, several copolymers whose RTP emission wavelength spanned from 422 to 582 nm have been reported by Ma and co‐workers. [ 52 ] Lactam‐based monomers N‐vinylpyrrolidone (NVP) and N‐vinylcaprolactam (NVCL) were integrated to afford a metal‐free amorphous RTP system (Figure 4b). Remarkably, the excellent biocompatibility, low cost, high hydrophilicity, and intrinsic multiple phosphorescence emission (Figure 4c,d) endowed these PNVP and PNVCL based RTP copolymers with a wide range of applications in materials science.…”