Room Temperature Phosphorescence Research Articles

Ultrafast dynamics of mCP and Br-mCP: Insights from transient absorption spectroscopy

Heavy atom activated organic room-temperature phosphorescence (RTP) has attracted considerable interest due to its high phosphorescence quantum yield and prolonged lifetime. This research provides a detailed analysis of the transient absorption spectroscopy of 1,3-Bis(N-carbazolyl)benzene (mCP) and 9,9'-(5-Bromo-1,3-phenylene)bis(9H-carbazole) (Br-mCP) in toluene solution. In the femtosecond transient absorption (fs-TA) spectroscopy of mCP, the excited state absorption (ESA) signal decreases at 630 nm while the triplet-triplet absorption (TTA) signal increases at 420 nm. Meanwhile, the isosbestic point observed at 455 nm indicates an intersystem crossing (ISC) lifetime of 15.4 ns. Moving on to the nanosecond transient absorption (ns-TA) spectroscopy, the TTA signal reaches its peak at 27.3 ns before decreasing, with the triplet lifetime of mCP measured at 2.8 μs. Br-mCP exhibits a similar dynamic evolution to mCP, but with a quicker ISC process (9.4 ns) and a longer triplet lifetime (3.9 μs). The quicker ISC process in Br-mCP is ascribed to the presence of heavy atom in the molecular structure, leading to an enhanced spin-orbit coupling constant (ξ(S1, T3)Br-mCP = 1.371 cm-1 > ξ(S1, T4)mCP = 0.060 cm-1). The prolonged triplet lifetime of Br-mCP (3.9 μs > 2.8 μs) results from its lower reorganization energy, effectively reducing non-radiative vibrational energy losses within the molecule. This work significantly enhances our understanding of RTP materials incorporating heavy atoms.

Electrochemical synthesis of multicolor carbon dots with room temperature phosphorescence to thermally activated delayed fluorescence via surface state modulation

Solid-state multicolor carbon dots (CDs) have attracted tremendous attention due to their wide applications. However, the fluorescence quenching of solid-state CDs occurs due to the π-π stacking or energy transfer between adjacent carbon dots. In addition, it is difficult to observe the afterglow of solid-state CDs due to their self-quenching and deliquescence. Here, electrochemically prepared multicolor CDs emit the solid-state fluorescence and afterglow emission with lifetimes up to 657 ms by embedding the CDs into urea matrix. More importantly, the surface amino groups and C = O bonds regulate the afterglow emission of CDs from phosphorescence and thermally activated delayed fluorescence at room temperature. Surface amino groups of multicolor CDs can enhance the spin–orbit coupling, increase the intersystem crossing (ISC) and reverse intersystem crossing (RISC). Thus it can promote the generation of triple excited states and regulate the singlet–triplet energy gap value from 0.384 to 0.026 eV. The formation of covalent bonds stabilizes the single and triple excited states and inhibits the non-radiative recombination, which achieves the enhanced fluorescence and visual afterglow of multicolor CDs. The fluorescence and afterglow CDs can be applied to dual signal imaging and anti-counterfeiting, which broadens the practical applications for solid-state CDs via surface state modulation.

Temperature‐Dependent Reversible Afterglow Between Green, Orange, and Red in Dual‐Delay Organic Doped Material

AbstractAchieving a wide‐range color‐tunable and dynamically long‐afterglow emission in a single‐doped system remains a challenge. In this study, a unique host‐guest doped material, TPA‐PTPQ/TPA, exhibits dual‐delay emission at 516 and 605 nm, both with long lifetimes of up to 108 and 145 ms, which derives from thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) mechanisms, respectively. Notably, this host‐guest material demonstrates a temperature‐dependent dynamically reversible afterglow characteristic, transitioning green, orange, and red with a substantial spectra shift of ≈90 nm under different temperature conditions. This phenomenon is due to the diverse temperature effect on TADF and RTP emissions. These remarkable luminescence properties are successfully applied in security checks and anti‐counterfeiting encryption. This study provides valuable insights into the design of dynamically reversible dual‐delay‐emissive long‐afterglow luminescent materials based on a host‐guest doping system.

Programmable Persistent Room Temperature Phosphorescence Switches through Wavelength-Selective Photoactivation.

Controlling multicolor persistent room-temperature phosphorescence (RTP) through photoirradiation holds fundamental significance but remains a significant challenge. In this study, we engineered a wavelength-selective photoresponsive system utilizing the Förster resonance energy transfer strategy. This system integrates a photoactivated long-lived luminescent material as the energy donor with a fluorescent photoswitch as the energy acceptor, facilitating programmable persistent luminescence switches. Distinct afterglow color states, such as initial nonemissive, green, yellow, and orange, were achieved through irradiation at 400 nm, 365 nm, and 254 nm, respectively. Based on this capability, we established an interacting network for multistate afterglow color switching among these four emissive states. In addition, we demonstrate the potential of this wavelength-selective photoresponsive system in the photo-controlled rewritable printing of multicolor afterglow images on a single thin film. This work represents a substantial step towards the fabrication of sophisticated wavelength-selective photoresponsive systems, potentially revolutionizing applications in optical data storage, security labeling, and smart displays by enabling precise control over photoresponsive behaviors under various photoirradiation wavelengths.

Organic Materials with Ultrabright Phosphorescence at Room Temperature under Physiological Conditions for Bioimaging.

In contrast to the high efficiency of room temperature phosphorescence in crystal states, the generally utilized nanoparticles of organic materials in bioimaging demonstrated sharply decreased performance by orders of magnitude under physiological conditions, badly limiting the realization of their unique advantages. This case, especially for organic red/near-infrared (NIR) phosphorescence materials, is not only the challenge present in reality but more importantly, for the theoretical problem of deeply understanding and avoiding the quenching effect by oxygen and water toward excited triplet states. Herein, thanks to the intelligent molecular design by the introduction of abundant hydrophobic chains and highly-branched structures, bright and persistent red/NIR phosphorescence under physiological conditions has been realized, which demonstrated the shielding effect towards oxygen, and strengthened the intermolecular interactions to suppress the non-radiative transitions. Accordingly, the record phosphorescence intensity of nanoparticles in bioimage, up to 8.21 ± 0.36 × 108 p s-1 cm-2 sr-1, was achieved, to realize the clear phosphorescence imaging of liver and tumors in living mice, even lymph nodes in rabbit models with high SBRs. This work afforded an efficient way to achieve the bright red/NIR phosphorescence nanoparticles, guiding their further applications in biology and medicine.

Tunable Helix Inversion and Circularly Polarized Luminescence in Cholesteric Liquid Crystal Copolymers with Room-Temperature Phosphorescence

Tunable Helix Inversion and Circularly Polarized Luminescence in Cholesteric Liquid Crystal Copolymers with Room-Temperature Phosphorescence

Study on the Influence of Host-Guest Structure and Polymer Introduction on the Afterglow Properties of Doped Crystals.

Due to their low cost, good biocompatibility, and ease of structural modification, organic long-persistent luminescence (LPL) materials have garnered significant attention in organic light-emitting diodes, biological imaging, information encryption, and chemical sensing. Efficient charge separation and carrier migration by the host-guest structure or using polymers and crystal to build rigid environments are effective ways of preparing high-performance materials with long-lasting afterglow. In this study, four types of crystalline materials (MODPA: DDF-O, MODPA: DDF-CHO, MODPA: DDF-Br, and MODPA: DDF-TRC) were prepared by a convenient host-guest doping method at room temperature under ambient conditions, i.e., in the presence of oxygen. The first three types exhibited long-lived charge-separated (CS) states and achieved visible LPL emissions with durations over 7, 4, and 2 s, respectively. More surprisingly, for the DDF-O material prepared with PMMA as the polymer substrate, the afterglow time of DDF-O: PMMA was longer than 10 s. The persistent room-temperature phosphorescence effect caused by different CS state generation efficiencies and rigid environment were the main reason for the difference in LPL duration. The fourth crystalline material was without charge separation and exhibited no LPL because it was not a D-A system. The research results indicate that the CS state generation efficiency and a rigid environment are the key factors affecting the LPL properties. This work provides new understandings in designing organic LPL materials.

Crosslink‐Enhanced Emission‐Dominated Design Strategy for Constructing Self‐Protective Carbonized Polymer Dots With Near‐Infrared Room‐Temperature Phosphorescence

AbstractSelf‐protective carbonized polymer dots (CPDs) with advantageous crosslinked nano‐structures have attracted considerable attention in metal‐free room temperature phosphorescence (RTP) materials, whereas their RTP emissions are still limited to short wavelength. Expanding their RTP emissions to Near‐Infrared (NIR) range is attractive but suffers from the difficulties in constructing narrow energy levels and inhibiting intense non‐radiative decay. Herein, a crosslink‐enhanced emission (CEE)‐dominated construction strategy was proposed, achieving desired NIR RTP (710 nm) in self‐protective CPDs for the first time. Structural factors, i.e., crosslinking (covalent‐bond CEE), conjugation (conjugated amine with bridging N−H and C=C group), and steric hindrance (confined‐domain CEE), were confirmed indispensable for triggering NIR RTP emission in CPDs. Contrast experiments and theoretical calculations further revealed the rationality of the design strategy originating from CEE in terms of promoting the narrow energy level emission of triplet excitons and inhibiting the non‐radiative quenching. This work not only firstly achieves NIR RTP in self‐protective CPDs but also helps understand the origin of NIR RTP to further guide the synthesis of diverse CPDs with efficient long‐wavelength RTP emission.

Generation, Inversion, and Amplification of Intrinsic Circularly Polarized Room Temperature Phosphorescence in Chiral Carbon Dots

Generation, Inversion, and Amplification of Intrinsic Circularly Polarized Room Temperature Phosphorescence in Chiral Carbon Dots

Photo-induced fluorescence discoloration and photo-responsive room temperature phosphorescence carbon dot-based composites with excellent reversibility and water resistance

Photo-stimulation responsive room temperature phosphorescence (RTP) carbon dots (CDs) have potential applications in advanced dynamic information encryption and anti-counterfeiting. However, the development of photo-responsive long-wavelength RTP CD materials with excellent reversibility and water resistance, as well as CD materials with both photo-induced fluorescence discoloration and photo-responsive reversible RTP properties, remains a challenge. Here, pyrene, which has a large conjugated structure, and 4-(1,2,2-triphenylvinyl)benzaldehyde, which has a tetraphenylethylene structure, were selected as the main raw materials to synthesize two CDs. Then, by introducing a PMMA matrix, reversible photo-responsive long-wavelength red RTP emission with a lifetime of 257 ms from a CD-based composite is realized for the first time, and the combination of photo-induced fluorescence discoloration and photo-responsive reversible yellow RTP with a lifetime of 287 ms is realized. Importantly, photo-responsive reversible RTP has excellent water resistance. The fluorescence discoloration was caused by photocyclization under long-term UV irradiation due to the presence of the tetraphenylethylene structure. The rigid environment provided by the PMMA matrix and the hydrogen bonds formed between the PMMA and CDs promote the generation of RTP. The photo-responsiveness of RTP is caused by the conversion of molecular oxygen (3O2) to singlet oxygen (1O2) under continuous UV irradiation. It is filled with 3O2 again after being placed in air to inactivate the RTP, thus achieving reversible RTP behavior. Owing to their excellent photo-responsive properties and water resistance, these materials have the potential to achieve repeatable dynamic information encryption and multilevel pattern anti-counterfeiting while also broadening the range of applications in water environments.

From Simple Probe to Smart Composites: Water-Soluble Pincer Complex With Multi-Stimuli-Responsive Luminescent Behaviors.

Water-soluble smart materials with multi-stimuli-responsiveness and ultra-long room-temperature phosphorescence (RTP) have garnered broad attention. Herein, a water-soluble terpyridine zinc complex (MeO-Tpy-Zn-OAc), featuring a simple donor-π-acceptor (D-π-A) structure is presented, which responds to a variety of stimuli, including changes in solvents, pH, temperature, and the addition of amino acids. Notably, MeO-Tpy-Zn-OAc functions as a fluorescence probe, capable of visually and selectively discriminating aspartate or histidine among other common amino acids in water. Additionally, when incorporated into polyvinyl alcohol (PVA) to form the composite MeO-Tpy-Zn-OAc@PVA, the material exhibits reversible writing, photochromism, and a prolonged RTP with a 14 s afterglow. These unique properties enable the composite to be utilized in potential applications such as secure data encryption and inkless printing.

Regulation of TADF and RTP Dual Emission via Internal and External Heavy-Atom Effects.

Organic materials with thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP) dual emission have attracted great attention in recent years, but the regulation mechanism via internal and external heavy atoms is not clear enough. Here, we carry out a systematic theoretical investigation on the photophysical properties of the materials by introducing aliphatic or aromatic bromine atoms. The molecule with aromatic bromine atoms exhibits obvious TADF owing to the effective reverse intersystem crossing (RISC) with matchable energy levels and enhanced spin orbit couplings, the molecule with aliphatic bromine atoms shows a long RTP lifetime because of the reduced nonradiative transition of triplet excitons, and the molecule with both aliphatic and aromatic bromine atoms presents balanced TADF and RTP emissions thanks to the synergy internal and external heavy-atom effects. Besides, the internal and external heavy atoms induce multisite intermolecular interactions, effectively suppressing the nonradiative process in the solid phase. The efficient RISC process and the suppressed nonradiative process of triplet excitons should be key to regulating the dual emission property. These findings and insights are of great importance for revealing the structure-performance relationship, providing theoretical guidance for the design of TADF and RTP dual emission molecules via internal and external heavy-atom effects.

Intramolecular Through‐Space Charge‐Transfer Effect for Achieving Room‐Temperature Phosphorescence in Amorphous Film

AbstractOrganic emitters that exhibit room‐temperature phosphorescence (RTP) in neat films have application potential for optoelectronic devices, bio‐imaging, and sensing. Due to molecular vibrations or rotations, the majority of triplet excitons recombine rapidly via non‐radiative processes in purely organic emitters, making it challenging to observe RTP in amorphous films. Here, a chemical strategy to enhance RTP in amorphous neat films is reported, by utilizing through‐space charge‐transfer (TSCT) effect induced by intramolecular steric hindrance. The donor and acceptor groups interact via spatial orbital overlaps, while molecular motions are suppressed simultaneously. As a result, triplets generated under photo‐excitation are stabilized in amorphous films, contributing to phosphorescence even at room temperature. The solvatochromic effect on the steady‐state and transient photoluminescence reveals the charge‐transfer feature of involved excited states, while the TSCT effect is further experimentally resolved by femtosecond transient absorption spectroscopy. The designed luminescent materials with pronounced TSCT effect show RTP in amorphous films, with lifetimes up to ≈40 ms, comparable to that in a rigid polymer host. Photoluminescence afterglow longer than 3 s is observed in neat films at room temperature. Therefore, it is demonstrated that utilizing intramolecular steric hindrance to stabilize long‐lived triplets leads to phosphorescence in amorphous films at room temperature.

High Efficiency Non‐Doped Organic Light Emitting Diodes Based on Pure Organic Room Temperature Phosphorescence by High‐Lying Singlet Exciton Fission

AbstractHeavy‐metal‐free pure organic room temperature phosphorescence (ORTP) holds great potential in the field of organic optoelectronic devices owing to low economic cost, simple preparation techniques, and high exciton utilization. However, it is still filled with challenges in realizing high efficiency organic light‐emitting diodes (OLEDs) and exploring the internal physical mechanism based on these ORTP molecules. Here, a high‐performance OLED induced by an unexpected interfacial spin‐mixing process between the ORTP molecule and interlayers is demonstrated, and the high efficiency electroluminescence (EL) mechanism is studied through magneto–electroluminescence (MEL) and magneto–photoluminescence (MPL) measurements. The steady‐state and transient PL properties imply that the interfacial effect is related to a high‐lying singlet fission (HLSF) process in the ORTP molecule itself. Further, the HLSF process and the corresponding energy level position are confirmed by the incident wavelength‐ and temperature‐dependent PL spectra and the magnetic‐field‐dependent transient PL. Finally, by optimizing the interfacial material adjacent to the emissive layer to utilize this interfacial spin mixing effect, a high‐efficiency non‐doped ORTP‐OLED with external quantum efficiency of 16% and CIE coordinates of (0.27, 0.49) is developed. The proposed mechanism during the EL process will give insight to produce more efficient OLEDs based on ORTP materials in the future.

Aqueous Afterglow Dispersion Enabling On‐Site Ratiometric Sensing of Mercury Ions

AbstractPollution caused by heavy metal ions has become a global issue owing to their severe threat to the ecological environment and human health. However, it remains a considerable challenge to detect heavy metal ions in an efficient, selective, and high signal‐to‐noise ratio way. Herein, a portable and sensitive method is presented to probe Hg2+ by using an ultralong afterglow dispersion. The in situ encapsulation of phosphorescent carbon dots (CDs) within rigid hydrogen‐bonded organic frameworks (HOFs) leads to ultralong room temperature phosphorescence (RTP) in water with a maximum lifetime of up to 974.86 ms. Moreover, the resultant CDs@HOFs material exhibits robust and long‐term RTP emission with enhanced performance under strongly acidic or alkaline conditions, which contributes to the practical detection of Hg2+ in water. As such, an efficient and sensitive afterglow probe is facilely fabricated by integrating CDs@HOFs with a Hg2+ probe Rhodamine B derivative (RhBTh), demonstrating selective sensing of Hg2+ with greatly improved signal‐to‐noise ratios based on the triplet‐singlet Förster resonance energy transfer system (TS‐FRET). This work not only provides a reliable and versatile method for realizing robust RTP emission in water, but also expands the applications of afterglow materials in the field of optical sensing of toxic analytes.

Accumulated in-situ spectral information analysis of room-temperature phosphorescence with time-gated bioimaging

This study introduces the time-gated analysis of room-temperature phosphorescence (RTP) for the in-situ analysis of the visible and spectral information of photons. Time-gated analysis is performed using a microscopic system consisting of a spectrometer, which is advantageous for in-situ analysis since it facilitates the real-time measurement of luminescence signal changes. An RTP material hybridized with a DNA aptamer that targets a specific protein enhances the intensity and lifetime of phosphorescence after selective recognition with the target protein. In addition, time-gated analysis allows for the millisecond-scale imaging of phosphorescence signals, excluding autofluorescence, and improves the signal-to-background ratio (SBR) through the accumulation of signals. While collecting the time-gated images and spectra of RTP and autofluorescent materials simultaneously, we develop a method for obtaining phosphorescence signals by means of selective exclusion of autofluorescence signals in simulated or real cell conditions. It is confirmed that the accumulated time-gated analysis can provide ample information about luminescence signals for bioimaging and biosensing applications.

Air-stable and ultralong room-temperature phosphorescence from doped poly(methyl methacrylate) for visual detection of volatile organic compounds

Room-temperature phosphorescence (RTP) has attracted significant attention due to its intriguing luminescence properties and potential applications in information storage, encryption, and sensing. Herein, we reported the facile fabrication of air-stable and ultralong RTP polymer films that exhibited remarkable and multiple stimuli responses. These films were composed of poly(methyl methacrylate) (PMMA) physically crosslinked with emitter molecules, resulting in transparent and flexible RTP materials. Remarkably, these polymer films emitted a bright RTP with a lifetime of 2.93 s, which was the best performance of PMMA materials reported. This exceptional performance was attributed to the abundant and robust physical interactions between the polymer chains and emitter molecules. Intriguingly, the RTP of these polymer films could be activated through consecutive UV irradiation, and quenched via thermal annealing in a controlled manner. The UV-activated RTP remained stable in humid air at room temperature over 1 week. Notably, the RTP of these flexible polymer films was sensitive to volatile organic compound (VOC) vapor. Upon exposure to VOC vapor, the RTP intensity of the polymer films rapidly decreased due to the disruption of their physically crosslinked microstructure. This unique sensitivity enabled the visual detection of VOCs in air by utilizing RTP polymers for the first time.

Light/Force-Responsive Room Temperature Phosphorescence in a Zinc-Organic Coordination Polymer.

A zinc-organic hybrid (1) with multifunctional room temperature phosphorescence (RTP) was synthesized. 1 presents light/force-sensitive RTP properties due to the photochromic behavior from gray to light yellow and the transition from crystalline to amorphous state, respectively. Furthermore, inkless printing and information encryption models were successfully constructed to prove their widespread application prospect.

Guest-Mediated Modulation of Photophysical Pathways in a Coronene Bisimide Cyclophane.

The properties and functions of chromophores utilized by nature are strongly affected by the environment formed by the protein structure in the cells surrounding them. This concept is transferred here to host-guest complexes with the encapsulated guests acting as an environmental stimulus. A new cyclophane host based on coronene bisimide is presented that can encapsulate a wide variety of planar guest molecules with binding constants up to (4.29 ± 0.32) × 1010 M-1 in chloroform. Depending on the properties of the chosen guest, the excited state deactivation of the coronene bisimide chromophore can be tuned by the formation of host-guest complexes toward fluorescence, exciplex formation, charge separation, room-temperature phosphorescence (RTP), or thermally activated delayed fluorescence (TADF). The photophysical processes were investigated by UV/vis absorption, emission, and femto- and nanosecond transient absorption spectroscopy. To enhance the TADF, two different strategies were used by employing suitable guests: the reduction of the singlet-triplet gap by exciplex formation and the external heavy atom effect. Altogether, by using supramolecular host-guest complexation, a versatile multimodal chromophore system is achieved with the coronene bisimide cyclophane.

Development of Pyrene Embedded Luminophore via π‐linker: Room Temperature Phosphorescence (RTP) and Sensing towards Nitroaromatics (NACs)

AbstractA pyrene base luminophore was designed and synthesised under ambient conditions using [4+2] annulation. The synthesised probe PYINDP exhibits good optical properties and emits greenish blue, with high colour purity in solid, solution, and thin film phases. In solution, the CIE coordinates were found to be (0.20, 0.48), and for an aggregated state emitting deep green colour, the CIE values are (0.27, 0.65). Room temperature phosphorescence (RTP) is generated by the luminophore PYINDP, owing to the ISC process. Moreover, the emitter demonstrated an excellent limit of detection values in detecting nitroaromatics (NACs). Bio‐imaging studies on HEK, A549 cell lines were successfully carried out to verify the staining capability of PYINDP in biological systems.