Organic Room Temperature Phosphorescence Materials Research Articles

Theoretical search of a simple characteristic for long-lived organic room-temperature phosphorescence materials with H aggregation

In RTP crystals, the overlapping area between H-aggregated planar dimer exhibits strong correlation with the physical parameters characterizing the RTP performance.

Room Temperature Phosphorescent (RTP) Thermoplastic Elastomers with Dual and Variable RTP Emission, Photo-Patterning Memory Effect, and Dynamic Deformation RTP Response.

Room temperature phosphorescent (RTP) polymers have advantages of strength, toughness, and processing and application flexibility over organic small molecular crystals, but the current RTP polymers are all from rigid plastics and involve chemical linkage and hydrogen and ionic bonds, and thermoplastic RTP elastomer has not been attempted and realized. Moreover, solution‐processed films by simply mixing polymers and organic RTP materials can only show weak and single blue RTP. Here it is presented that such elastomer films, once thermomechanically plasticized, can emit bright and long‐lived dual RTP. Moreover, they exhibit photo‐activation memory effect, variable RTP colors and dynamic deformation RTP response. These results reveal that thermoplasticizing has altered the dispersion states and micro‐environment of RTP molecules in matrix, and the cohesion of elastic polymer itself can also greatly restrict non‐radiative relaxations to boost both blue mono‐molecular and yellow micro‐crystalline RTP. This work provides an effective and versatile processing strategy for tuning and enhancing the RTP properties of doped RTP polymers.

Emission‐Tunable Room‐Temperature Phosphorescent Polymers Based on Dynamic Reversible Supramolecule‐Mediated Photocrosslinking

AbstractPure organic room‐temperature phosphorescence (RTP) materials can be used in optoelectronics, biochemical equipment, sensors and biological imaging. In the past few years, dynamic covalent chemistry has attracted significant attention because it provides a new way to produce intelligent optical materials with feedback functions. Two polymers are synthesized through supramolecular‐mediated [4+4] photocyclodimerization of anthracene, which can be reversibly transformed by photoreversible dynamic covalent bonds. The polymers show decent phosphorescence emission with different colors at room temperature, achieving the conversion between blue phosphorescence and cyan phosphorescence. This study provides a novel method for designing and synthesizing pure organic RTP materials with tunable emissions through dynamic covalent bonds.

Supramolecular Purely Organic Room-Temperature Phosphorescence.

In recent years, purely organic room-temperature phosphorescence (RTP) has aroused wide concern and promotes the development of the supramolecular phosphorescence. Different from organic crystallization, polymerization, or matrix rigidification, supramolecular strategy mainly takes advantage of the synergy between supramolecular co-assembly and strong binding by macrocyclic host compounds (cucurbit[n]urils, cyclodextrins, etc.) to overcome deficiencies such as poor processability and water solubility and improves RTP materials' quantum efficiency and lifetime in the solid state or in an aqueous solution. Meanwhile, it expands application, especially in aqueous solution, in cell imaging. Therefore, supramolecular phosphorescence will become a new growth point and will have broad application prospects in chemistry, biology, and material science.This Account focuses on the uniquely synergetic advantages of co-assembly and host-guest interaction from macrocyclic hosts for enhancing RTP. This Account starts with a brief introduction of the recent development of organic RTP materials as well as the host-guest interaction and co-assembly. Then, we introduce a supramolecular solid-state RTP strategy involving an ultrahigh phosphorescent quantum yield via the tight encapsulation of macrocyclic host cucurbit[6]uril, an ultralong lifetime via changing the substituents of phosphors, and long-lived and bright RTP by the synergy of host-guest interaction and polymerization. Meanwhile, the applications of solid-state RTP materials for anti-counterfeiting and data encryption are presented. The third part will be the water-phase supramolecular phosphorescence systems constructed by water-soluble macrocyclic host cucurbit[8]uril. Host-guest interaction and polymerization worked together toward efficient phosphorescence in aqueous solution, and the multi-stage assembly promoted phosphorescent applications such as cell targeted imaging and energy transfer. A humidity sensor and data encryption by the conversion of supramolecular hydrogels and xerogels are also involved. In the summary section, we present perspectives and possible research directions for supramolecular phosphorescence.Furthermore, on the basis of previous research, we would like to conclude and propose the developing concept of "macrocycles enhance guest's phosphorescence", and this concept not only means that the macrocyclic host limits the movement of the guest compound or promotes interactions between guest compounds but also involves the synergetic enhancement centered on macrocyclic compounds via multi-stage supramolecular assembly which further improves the efficiency of RTP, water solubility, and biocompatibility. And we believe that this concept will be able, together with theory of "assembly-induced emission" and "aggregation-induced emission", to accelerate the development of purely organic RTP materials.

Supramolecular self-assembling strategy for constructing cucurbit[6]uril derivative-based amorphous pure organic room-temperature phosphorescence complex featuring extra-high efficiency

The preparation of amorphous pure organic room-temperature phosphorescence materials with high efficiency is still a challenging task. Herein, we introduce a CB[6] derivative-based supramolecular self-assembling strategy. A water soluble and ellipsoidal deformed CB[6] derivative is used to self-assemble with 4-(4-bromophenyl)-1-methylpyridin-1-ium chloride, bromide and hexafluorophosphate in water. After freeze-drying, the obtained amorphous complexes exhibit brilliant green phosphorescence emission under ambient conditions, with phosphorescence efficiency up to 59%, 60% and 72%, respectively. This is the first report of amorphous non-polymeric pure organic room-temperature phosphorescence with such a high efficiency. In view of the dynamic self-assembling property, the complexes are responsive to water, which could enable information encryption.

Activating Room‐Temperature Phosphorescence of Organic Luminophores via External Heavy‐Atom Effect and Rigidity of Ionic Polymer Matrix**

Pure organic room-temperature phosphorescence (RTP) materials have attracted wide attention for their easy preparation, low toxicity, and applications in various fields like bioimaging and anti-counterfeiting. Developing phosphorescent systems with more universality and less difficulty in synthesis has long been the pursuit of materials scientists. By employing a polymeric quaternary ammonium salt with an ionic bonding matrix and heavy atoms, commercial fluorescent dyes are directly endowed with phosphorescence emission. In a single amorphous polymer, the external heavy-atom effect generates excited triplet states and the rigid polymer matrix stabilizes them. This study put forward a new general strategy to design and develop pure organic RTP materials starting from existing library of organic dyes without complicated chemical synthesis.

Multistage Stimulus‐Responsive Room Temperature Phosphorescence Based on Host–Guest Doping Systems

AbstractCompared with inorganic long‐lasting luminescent materials, organic room temperature phosphorescent (RTP) ones show several advantages, such as flexibility, transparency, solubility and color adjustability. However, organic RTP materials close to commercialization are still to be developed. In this work, we developed a new host–guest doping system with stimulus‐responsive RTP characteristics, in which triphenylphosphine oxide (OPph3) acted host and benzo(dibenzo)phenothiazine dioxide derivatives as guests. Turn‐on RTP effect was realized by mixing them together through co‐crystallization or grinding, in which the efficient energy transfer from host to guest and the strong intersystem crossing (ISC) ability of the guest have played significant role. Further on, multistage stimulus‐responsive RTP characteristics from grinding to chemical stimulus were achieved via introducing pyridine group into the guest molecule. In addition, the anti‐counterfeiting printings were realized for these materials through various methods, including stylus printing, thermal printing and inkjet printing, which brings RTP materials closer to commercialization.

Multistage Stimulus-Responsive Room Temperature Phosphorescence Based on Host-Guest Doping Systems.

Compared with inorganic long-lasting luminescent materials, organic room temperature phosphorescent (RTP) ones show several advantages, such as flexibility, transparency, solubility and color adjustability. However, organic RTP materials close to commercialization are still to be developed. In this work, we developed a new host-guest doping system with stimulus-responsive RTP characteristics, in which triphenylphosphine oxide (OPph3 ) acted host and benzo(dibenzo)phenothiazine dioxide derivatives as guests. Turn-on RTP effect was realized by mixing them together through co-crystallization or grinding, in which the efficient energy transfer from host to guest and the strong intersystem crossing (ISC) ability of the guest have played significant role. Further on, multistage stimulus-responsive RTP characteristics from grinding to chemical stimulus were achieved via introducing pyridine group into the guest molecule. In addition, the anti-counterfeiting printings were realized for these materials through various methods, including stylus printing, thermal printing and inkjet printing, which brings RTP materials closer to commercialization.

Activating Room‐Temperature Phosphorescence of Organic Luminophores via External Heavy‐Atom Effect and Rigidity of Ionic Polymer Matrix**

AbstractPure organic room‐temperature phosphorescence (RTP) materials have attracted wide attention for their easy preparation, low toxicity, and applications in various fields like bioimaging and anti‐counterfeiting. Developing phosphorescent systems with more universality and less difficulty in synthesis has long been the pursuit of materials scientists. By employing a polymeric quaternary ammonium salt with an ionic bonding matrix and heavy atoms, commercial fluorescent dyes are directly endowed with phosphorescence emission. In a single amorphous polymer, the external heavy‐atom effect generates excited triplet states and the rigid polymer matrix stabilizes them. This study put forward a new general strategy to design and develop pure organic RTP materials starting from existing library of organic dyes without complicated chemical synthesis.

Deep‐Blue Ultralong Room‐Temperature Phosphorescence from Halogen‐Free Organic Materials through Cage Effect for Various Applications

AbstractOrganic room‐temperature phosphors with high performances are of great importance for broad range of potential applications. Herein, a new concept of cage effect is proposed to effectively promote room‐temperature phosphorescence (RTP) property of organic materials. A novel phosphor, bearing electron‐donating carbazole and electron‐accepting boronate ester moieties (CBBU) is designed and synthesized. CBBU crystals show multiple photoluminescence including concomitant fluorescence, thermally activated delayed fluorescence (TADF), and RTP. Further doping CBBU in boronate ester crystals (DB/CBBU) boosts remarkably deep‐blue RTP emission with CIE coordinates (0.15, 0.09) and a lifetime of 3.69 s, which is longer by four orders of magnitude than that of neat CBBU crystals. To the best of knowledge, it is the longest deep‐blue organic RTP materials reported so far. To understand this phenomenon, cage effect in terms of bending, twisting, and crowding degrees, as well as interaction of chromophores with cages has been taken into consideration. The results demonstrate that the strong cage effect alleviates effectively molecular motion of chromophores and then promotes simultaneously their RTP efficiency and lifetime. Similar results have also been found in a series of boronate ester derivatives. Furthermore, applications of the efficient RTP materials for temperature measurements, thermal transition detection, and UV sensing are exploited.

Molecular conformation dependence of phosphorescence lifetime in organic aggregates

Organic bulk crystal with room-temperature phosphorescence (RTP) is normally fabricated into nanoparticles (NPs) for biological applications, accompanying with inevitable change in RTP lifetime and molecular conformation. By using molecular dynamics and quantum chemistry methods, the difluoroboron β-diketonate (BF2bdk) compound (Br-NpCzBF2) was explored to uncover the molecular conformation-dependent RTP from crystal to NPs. We proposed that from crystal to amorphous aggregates, the distorted BF2bdk group caused by the weakened intermolecular B–F⋯H–C hydrogen bonds convert the T1 from hybridized local and charge transfer to locally excited states. Such change strengthens the vibronic coupling effect on the CC stretching vibration, and enormously accelerates the nonradiative decay rate of T1→S0 by 1–2 orders of magnitude. Consequently, the RTP lifetime is shortened from 566 μs in crystal to about 10 μs in amorphous aggregates, which is consistent with the experiments. This work provides new insight into the RTP mechanism and opens a novel design avenue for designing organic RTP materials in biological fields.

A Permanent Porous Hydrogen-Bonded Framework with Room-Temperature Phosphorescence

Hydrogen-bonded organic frameworks (HOFs) based on metal-free organic materials with permanent porosity and phosphorescence are rarely reported. Herein, we report a pure organic phosphor of 1,3,5-tris((4-(9H-carbazol-9-yl)phenyl)methanone-1-yl)benzene (BPMCz) as a suitable building block to construct robust HOF materials. Apart from a good thermal stability, BPMCz-P1 exhibited a comparatively high CO2 adsorption and room-temperature phosphorescence with a lifetime of 1.8 ms under ambient conditions. The experimental and theoretical data clearly indicate that aromatic carbonyl groups not only play a critical role in forming intermolecular hydrogen bonds to construct HOFs but also facilitate π–π interactions to enable long-lived phosphorescence. The introduction of carbonyl groups in BPMCz-P1 successfully construct a metal-free porous framework with phosphorescence emission. This study will not only provide valuable guidelines for the construction of new HOFs with luminescent properties but also expand the scope of organic room-temperature phosphorescent materials and their applications.

High Performance of Simple Organic Phosphorescence Host-Guest Materials and their Application in Time-Resolved Bioimaging.

The study of purely organic room-temperature phosphorescence (RTP) has drawn increasing attention because of its considerable theoretical research and practical application value. Currently, organic RTP materials with both high efficiency (ΦP > 20%) and a long lifetime (τP > 10 s) in air are still scarce due to the lack of related design guidance. Here, a new strategy to increase the phosphorescence performance of organic materials by integrating the RTP host and RTP guest in one doping system to form a triplet exciplex, is reported. With these materials, the high-contrast labeling of tumors in living mice and encrypted patterns in thermal printing are both successfully realized by taking advantage of both the long afterglow time (up to 25min in aqueous media) and high phosphorescence efficiency (43%).

Ultralong organic room-temperature phosphorescence of electron-donating and commercially available host and guest molecules through efficient Förster resonance energy transfer

Ultralong organic room-temperature phosphorescence (RTP) materials have attracted tremendous attention recently due to their diverse applications. Several ultralong organic RTP materials mimicking the host-guest architecture of inorganic systems have been exploited successfully. However, complicated synthesis and high expenditure are still inevitable in these studies. Herein, we develop a series of novel host-guest organic phosphorescence systems, in which all luminophores are electron-rich, commercially available and halogen-atom-free. The maximum phosphorescence efficiency and the longest lifetime could reach 23.6% and 362 ms, respectively. Experimental results and theoretical calculation indicate that the host molecules not only play a vital role in providing a rigid environment to suppress non-radiative decay of the guest, but also show a synergistic effect to the guest through Forster resonance energy transfer (FRET). The commercial availability, facile preparation and unique properties also make these new host-guest materials an excellent candidate for the anti-counterfeiting application. This work will inspire researchers to develop new RTP systems with different wavelengths from commercially available luminophores.

Recent Advances of Polymer-Based Pure Organic Room Temperature Phosphorescent Materials.

Room temperature phosphorescence (RTP) has attracted broad attention due to their long lifetimes, large Stokes shift, and widespread applications. Achieving RTP emission has long been a challenging task under common conditions, for the necessary requirements of promoting intersystem crossing processes and suppressing nonradiative transitions are always tough to meet. Over the past decade, RTP has been obtained through several specific strategies, among which an important method lies in immobilizing phosphors into polymer matrices. Via the effect of steric overcrowding exerted by the polymeric structures, the phosphorescence of the initial phosphors can be promoted significantly. Hence, polymer-based pure organic materials have proved to be one newly emerging subject in the field of RTP materials. In this review article, the progresses of polymer-based pure organic room temperature phosphorescent materials are elaborated from four main approaches, including doped polymer systems, copolymer systems, homopolymer systems, and host-guest complexation systems, whereby the design principles, synthesis methods, possible mechanisms, and applications are summarized and discussed in detail.

Tailoring the strength and number of halogen bonds toward room temperature phosphorescent micro‐cocrystals

AbstractOrganic room temperature phosphorescent materials are very limited to date. Halogen bonding interactions not only promote the intersystem crossing process, but also act as cement and dilute solution, preventing the aggregation induced quenching. Herein, four cocrystals using phenazine (PhZ) as halogen‐bonded acceptor and 1,2,4,5‐tetrabromo‐3,6‐diiodobenzene (BrFB) or 1,2,4,5‐tetrafluoro‐3,6‐diiodobenzene (IFB) as halogen‐bonded donor have been successfully synthesized in definite stoichiometric ratio (PhZ : XFB = 1:1 and 2:1) through simple solvent evaporation method. Among the four cocrystals, the halogen bonding interactions play an important role in assembling properties and the large red spots on Hirshfeld surface imply the strong strength. Notably, the IFB‐PhZ cocrystals exhibit a phosphorescence emission at peak of 733 nm with a lifetime up to 159 µs. The results further suggest the importance of the strength and number of halogen bonds to design organic room temperature phosphorescent materials.

Boosting Room Temperature Phosphorescence Performance by Alkyl Modification for Intravital Orthotopic Lung Tumor Imaging.

Pure organic persistent room temperature phosphorescence (RTP) materials have attracted wide attention owing to their great potential in various applications, particularly in bioimaging. However, it is still a challenge to manufacture organic RTP materials possessing quite high efficiency and long lifetime, owing to the high requirements for triplet excitons. In this study, a series of keto derivatives with efficient RTP in crystals are developed through the regulation of molecular aggregation states by simple alkyl groups, resulting in impressive luminescence performance with a longer lifetime and higher efficiency of up to 868ms and 51.59%, respectively. All the alkyl-substituted derivatives exhibit bright RTP intensities after heavy grinding with a pestle, indicating their robust RTP features, which are suitable for many fields. Encouraged by the excellent RTP performance of these luminogens in the crystalline state, successful orthotopic lung tumor imaging with a high signal-to-background ratio (SBR) of 65 is demonstrated in this study to provide the promise of pure organic RTP materials for disease diagnosis, which hold the advantages of low autofluorescence interference and high signal-to-background ratio.

Recent Advances of Pure Organic Room Temperature Phosphorescence Materials for Bioimaging Applications

Bioimaging, as a powerful and helpful tool, which allows people to investigate deeply within living organisms, has contributed a lot for both clinical theranostics and scientific research. Pure organic room temperature phosphorescence(RTP) materials with the unique features of ultralong luminescence lifetime and large Stokes shift, can efficiently avoid biological autofluorescence and scattered light through a time-resolved imaging modality, and thus are attracting increasing attention. This review classifies pure organic RTP materials into three categories, including small molecule RTP materials, polymer RTP materials and supramolecular RTP materials, and summarizes the recent advances of pure organic RTP materials for bioimaging applications.

The development of phosphorescent probes for in vitro and in vivo bioimaging.

Phosphorescence is a process that slowly releases the photoexcitation energy after the removal of the excitation source. Although transition metal complexes and purely organic room-temperature phosphorescence (RTP) materials show excellent phosphorescence property, their applications in in vitro and in vivo bioimaging are limited due to their poor solubility in water. To overcome this issue, phosphorescent materials are modified with amphiphilic or hydrophilic polymers to endow them with biocompatibility. This review focuses on recent advances in the development of phosphorescent probes for in vitro and in vivo bioimaging. The photophysical mechanism and the design principles of transition metal complexes and purely organic RTP materials for the stabilization of the triplet excited state for enhanced phosphorescence are first discussed. Then, the applications in in vitro and in vivo bioimaging using transition metal complexes including iridium(iii) complexes, platinum(ii) complexes, rhodium(i) complexes, and purely organic RTP materials are summarized. Finally, the current challenges and perspectives for these emerging materials in bioimaging are discussed.

Tunable-Emission Amorphous Room-Temperature Phosphorescent Polymers Based on Thermoreversible Dynamic Covalent Bonds.

Pure organic room-temperature phosphorescence (RTP) materials are useful for photoelectric, biochemical devices, and bioimaging sensors. In the last few years, dynamic covalent chemistry has aroused substantial attention as it offers a way to create intelligent materials with feedback and response functions. Through a Diels-Alder reaction, a [4+2] cycloaddition reaction between dienes and dienophiles, three polymers were synthesized that can be reversibly transformed by thermally reversible dynamic covalent bonds. All polymers show decent RTP emission with different colors. For the poly-Br-An solid, the absolute phosphorescence quantum yield reaches up to 12 %. This study provides a new method for the rational design and synthesis of tunable-emission organic RTP materials via dynamic covalent bonds.