Long-Lived Organic Room-Temperature Phosphorescence from Amorphous Polymer Systems

Abstract

Metrics & MoreArticle Recommendations * sı Supporting Information CONSPECTUS: Long-lived organic room-temperature phosphorescence (RTP) materials have recently drawn extensive attention because of their promising applications in information security, biological imaging, optoelectronic devices, and intelligent sensors.In contrast to conventional fluorescence, the RTP phenomenon originates from the slow radiative transition of triplet excitons. Thus, enhancing the intersystem crossing (ISC) rate from the lowest excited singlet state (S 1 ) to the excited triplet state and suppressing the nonradiative relaxation channels of the lowest excited triplet state (T 1 ) are reasonable methods for realizing highly efficient RTP in purely organic materials. Over the past few decades, many strategies have been designed on the basis of the above two crucial factors. The introduction of heavy atoms, aromatic carbonyl groups, and other heteroatoms with abundant lone-pair electrons has been demonstrated to strengthen the spin− orbit coupling, thereby successfully facilitating the ISC process. Furthermore, the rigid environment is commonly constructed through crystal engineering to restrict intramolecular motions and intermolecular collisions to decrease excited-state energy dissipation. However, most crystal-based organic RTP materials suffer from poor processability, flexibility, and reproducibility, becoming a thorny obstacle to their practical application. Amorphous organic polymers with long-lived RTP characteristics are more competitive in materials science. The intertwined structures and long chains of polymers not only ensure the rigid environment with multiple interactions but also protect triplet excitons from the surroundings, which are conducive to realizing ultralong and bright RTP emission. Exploring the fabrication strategies, intrinsic mechanisms, and practical applications of organic long-lived RTP polymers is highly desirable but remains a formidable challenge. In particular, intelligent organic RTP polymer systems that are capable of dynamically responding to external stimuli (e.g., light, temperature, oxygen, and humidity) have been rarely reported. To develop multifunctional RTP materials and expand their potential applications, a great amount of effort has been expended. This Account gives a summary of the significant advances in amorphous organic RTP polymer systems, especially smart stimulusresponsive ones, focusing on the construction of a rigid environment to suppress nonradiative deactivation by abundant inter/ intramolecular interactions. The typical interactions in RTP polymer systems mainly include hydrogen bonding, ionic bonding, and covalent bonding, which can change the molecular electronic structures and affect the energy dissipation channels of the excited states. An in-depth understanding of intrinsic mechanisms and an extensive exploration of potential applications for excitationdependent color-tunable, ultraviolet (UV) irradiation-activated, temperature-dependent, water-responsive, and circula...

Cross‐linking enhanced room‐temperature phosphorescence of carbon dots

“…[8][9][10] In general, RTP is difficult to achieve at room temperature due to the spin prohibition of triplet exciton transitions and the fact that triplet excitons are easily quenched by oxygen and other nonradiative processes. [11][12][13] Researchers would achieve RTP by the following methods: (1) doping rare earth metal ions or heteroatoms into the phosphors to facilitate intersystem crossing (ISC) processes; (2) embedding phosphors into rigid substrates, such as polymers, ionic crystals, amorphous materials, and macrocyclic molecules to suppress vibration and rotation; and (3) selecting rigid precursors and using self-assembly to regulate molecular stacking patterns, restricting nonradiative processes and protecting triplet excitons. [14][15][16][17] Over the past decade, researchers have made a steady stream of breakthroughs in the preparation of RTP materials, targeting mainly inorganic complexes or metal-free organic compounds.…”

“…Although inorganic RTP materials with prolonged light emission are actively being sought for many applications including optoelectronic devices, photocatalysis, and emergency signage, 4–7 they are less suitable for applications such as anticounterfeiting and bioimaging materials, where bright, subsecond afterglow is required 8–10 . In general, RTP is difficult to achieve at room temperature due to the spin prohibition of triplet exciton transitions and the fact that triplet excitons are easily quenched by oxygen and other nonradiative processes 11–13 . Researchers would achieve RTP by the following methods: (1) doping rare earth metal ions or heteroatoms into the phosphors to facilitate intersystem crossing (ISC) processes; (2) embedding phosphors into rigid substrates, such as polymers, ionic crystals, amorphous materials, and macrocyclic molecules to suppress vibration and rotation; and (3) selecting rigid precursors and using self‐assembly to regulate molecular stacking patterns, restricting nonradiative processes and protecting triplet excitons 14–17 .…”

Cluster-luminescent polysiloxane nanomaterials: adjustable full-color ultralong room temperature phosphorescence and a highly sensitive response to silver ions

“…21 However, CIP efficiency is highly dependent on the morphology of the material, requiring high crystal quality (for small molecules) 22,23 or large molecular weight (for polymers). 24,25 Therefore, it is difficult to realize the CIP of amorphous nanomaterials which have huge application potential in biological imaging, optoelectronic devices, and information storage. It is necessary to develop a simple method to obtain nanomaterials with long lifetime CIP.…”

A π-orbital model to study substituent effects in organic room-temperature phosphorescent materials

“…Room temperature phosphorescence (RTP) in organic materials has aroused great attention owing to their potential applications in sensing, bioimaging, X-ray scintillators, etc. [1][2][3][4][5][6][7] There are two inevitable obstacles to obtaining the RTP of organic compounds: one is the scarce population of triplet excitons caused by the spin-forbidden intersystem crossing (ISC) from singlet to triplet excited states, and the other is the ultrafast nonradiative deactivation of triplet excitons under ambient conditions. Normally, introducing n-electron groups into p-conjugated chromophores is favourable for accelerating the ISC process, 8,9 and rigid environments are beneficial to stabilize the triplet excitons by restricting molecular motions through multiple intermolecular interactions; the combination of these two strategies can trigger efficient organic RTP.…”

“…[16][17][18][19][20][21][22][23][24][25][26] Recently, the electron-donating groups (EDGs) have been demonstrated to weaken the intermolecular interaction among the adjacent p-units, which is harmful for the stabilization of triplet excitons, thereby reducing the RTP performance. [16][17][18] For example, Ehsan et al reported that 4H-benzo [9,1]quinolizino [3,4,5,6,7-defg]acridine-4,8,12-trione (QAT) emits a bright RTP with an efficiency (F p ) of 42.0% in crystals, whereas the tert-butyl fused QAT (QAT-tBu) shows a faint RTP but bright fluorescence with an efficiency (F f ) of 11.0%. 18 In contrast, several studies found that the involvement of EDGs can promote RTP efficiency (F p ) and prolong RTP lifetime (t p ); e.g., the F p was increased from 0.9% in thioxanthone (TX) to 11.7% in methoxy-substituted TX (TX-OMe); 22,23 the t p was prolonged from 0.02 ms in N-methyl phthalimide (MP) to 39.9 ms in norbornyl (NB) fused MP (MP-NB).…”