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Suppressed Triplet Exciton Diffusion Due to Small Orbital Overlap as a Key Design Factor for Ultralong-Lived Room-Temperature Phosphorescence in Molecular Crystals
摘要： Persistent room-temperature phosphorescence (RTP) under ambient conditions is attracting attention due to its strong potential for applications in bioimaging, sensing, or optical recording. Molecular packing leading to a rigid crystalline structure that minimizes nonradiative pathways from triplet state is often investigated for efficient RTP. However, for complex conjugated systems a key strategy to suppress the nonradiative deactivation is not found yet. Here, the origin of small rates of a nonradiative decay process from triplet states of conjugated molecular crystals showing RTP is reported. Optical microscopy analysis showed that, despite a favorable molecular stacking, an aromatic crystal with strong RTP is characterized by small diffusion length and small values of the diffusion coefficient of triplet excitons. Quantum chemical calculations reveal a large overlap between the lowest unoccupied molecular orbitals but very small overlap between the highest occupied molecular orbitals (HOMOs). Inefficient electron exchange caused by the small overlap of HOMOs prevents triplet excitons from diffusing over long distances and consequently from quenching at defect sites inside the crystal or at the crystal surface. These results will allow design of comprehensive molecular structures to obtain molecular solids with more efficient RTP.
关键词： suppressed nonradiative rate,persistent room-temperature phosphorescence,triplet exciton diffusion,molecular orbital overlap,fluorescence microscopy
更新于2025-09-23 15:23:52
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Luminescent TOP Nanosensors for Simultaneously Measuring Temperature, Oxygen, and pH at a Single Excitation Wavelength
摘要： Two nanosensors for simultaneous optical measurements of the bioanalytically and biologically relevant analytes temperature (“T”), oxygen (“O”), and pH (“P”) have been designed. These “TOP” nanosensors are based on 100 nm-sized silica-coated polystyrene nanoparticles (PS-NPs) doped with a near infrared emissive oxygen- and temperature-sensitive chromium(III) complex ([Cr(ddpd)2][BPh4]3, CrBPh4) and an inert reference dye (Nile Red, NR or 5,10,15,20-tetrakis-(pentafluorophenyl) porphyrin, TFPP) and are covalently labeled with pH-sensitive fluorescein isothiocyanate (FITC). These emitters can be excited at the same wavelength and reveal spectrally distinguishable emission bands allowing for ratiometric intensity-based and time-resolved studies in the visible and near infrared wavelength region. Studies in PBS buffer solutions and in a model body liquid demonstrate the applicability of these nanosensors for the sensitive fluorescence readout of TOP simultaneously at the same position.
关键词： lifetime,fluorescence,chromium(III) complex,oxygen/pH/temperature biosensor,optical multianalyte nanosensors,phosphorescence
更新于2025-09-23 15:22:29
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Controlling the fluorescence and room-temperature phosphorescence behaviour of carbon nanodots with inorganic crystalline nanocomposites
摘要： There is a significant drive to identify alternative materials that exhibit room temperature phosphorescence for technologies including bio-imaging, photodynamic therapy and organic light-emitting diodes. Ideally, these materials should be non-toxic and cheap, and it will be possible to control their photoluminescent properties. This was achieved here by embedding carbon nanodots within crystalline particles of alkaline earth carbonates, sulphates and oxalates. The resultant nanocomposites are luminescent and exhibit a bright, sub-second lifetime afterglow. Importantly, the excited state lifetimes, and steady-state and afterglow colours can all be systematically controlled by varying the cations and anions in the host inorganic phase, due to the influence of the cation size and material density on emissive and non-emissive electronic transitions. This simple strategy provides a flexible route for generating materials with specific, phosphorescent properties and is an exciting alternative to approaches relying on the synthesis of custom-made luminescent organic molecules.
关键词： room temperature phosphorescence,photoluminescence,heavy atom effect,carbon nanodots,nanocomposites
更新于2025-09-23 15:22:29
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Spectroscopic and Quantum-Chemical Studies of Halogen-Containing Derivatives of Poly-N-Epoxypropylcarbazole
摘要： The results of a study of the optical properties of conducting polymers, namely, derivatives of poly-N-epoxypropylcarbazole (PEPC) with heavy atoms, are presented. It is shown that a heavy atom in the structure of a polymer molecule leads to bathochromic shifts in the absorption, fluorescence, and phosphorescence spectra. This is a consequence of a decrease in the energy of the electron levels due to a change in the electron density distribution over the π-electron system in the chromophores of 2IPEPC and 3BrPEPC. Two bands can be distinguished in the fluorescence spectra of PEPC with heavy atoms, just as in the parent polymer. The emission band with a maximum at 380 nm belongs to the monomer luminescent centers and the long-wavelength emission with a maximum at about 420 nm to the polymer excimers. A heavy atom changes the ratio of the intensities of the monomer and excimer bands. The fluorescence lifetimes also decrease in the presence of a heavy atom. Quantum-chemical estimation of the intramolecular transition constants has shown that the probability of the singlet–triplet intercombination conversion in the halogen-containing PEPCs is higher in PEPC. This leads to a markedly stronger phosphorescence of the iodine and bromine-containing polymers and a shorter luminescence lifetime. The obtained results can be used in the development of composite materials based on photoconductive polymers for photovoltaics and optoelectronics.
关键词： optoelectronics,phosphorescence,conducting polymers,poly-N-epoxypropylcarbazole,fluorescence,heavy atoms,bathochromic shifts,photovoltaics,quantum-chemical estimation
更新于2025-09-23 15:21:21
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Ultralong Lifetime Room Temperature Phosphorescence and Dual-band Waveguide Behavior of Phosphoramidic Acid Oligomers
摘要： In recent years, some natural or synthetic non-conjugated luminescence systems have attracted much attention. However, the phosphorescent properties of these materials are generally not very satisfactory due to the lack of special molecular design. In this work, the phosphoramidic acid is introduced into the oligomer matrix to construct a non-conjugated photoluminescence system with ultralong phosphorescence lifetime up to 376.5 to 776.9 ms and high phosphorescence quantum yield (4.6-10.5 %). At the same time, the new system also displays good thermo-processing properties, vitreous solid and optical waveguide behavior.
关键词： Room temperature phosphorescence,ultralong phosphorescence lifetime,phosphoramidic acid oligomers,optical waveguide behavior
更新于2025-09-23 15:21:01
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Circularly Polarized Rooma??Temperature Phosphorescence and Encapsulation Engineering for MOFa??Based Fluorescent/Phosphorescent WLEDs
摘要： Optical materials with circularly polarized luminescence and room temperature phosphorescence currently attract great attention owing to their unique optoelectronic properties. Herein, via the coordination-induced assembly strategy, a homochiral metal–organic framework (MOF) 1 with high stability and porosity is successfully synthesized by using the achiral triphenylamine-based molecule as the building block. Remarkably, MOF 1 shows circularly polarized luminescence and phosphorescence at room temperature simultaneously, also with excellent anisotropic optical properties. Furthermore, MOF 1 can serve as a nanocontainer to construct dye-encapsulated host–guest systems. Importantly, the multicolor emissions including white-light emission can be achieved. The corresponding color rendering index and correlated color temperature values of light emitting device are 73 and 5541 K, when using dye-loaded MOF 1?RhB 10 (CIE: 0.33, 0.33) as single-phase white light-emitting phosphor. This study first reports circularly polarized phosphorescence based on MOF without precious metals under ambient conditions, and also is first time for phosphorescent polarized materials with high porosity. These results will open up a new pathway to the design of porous chiroptical materials and white-light materials.
关键词： circularly polarized luminescence,host–guest system,room temperature phosphorescence,white light emitting devices,metal–organic frameworks
更新于2025-09-23 15:21:01
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Selfa??assembled Helical Arrays for Stabilizing the Triplet State
摘要： Room-temperature phosphorescence of metal and heavy atom-free organic molecules has emerged as an area of great potential in the recent past. A rational design played a critical role in controlling the molecular ordering to impart efficient intersystem crossing and stabilize the triplet state to achieve room-temperature ultralong phosphorescence. However, in most of the cases, the strategies followed to strengthen phosphorescence efficiency have resulted in a reduced lifetime, and the available nearly degenerate singlet-triplet energy levels impart a natural competition between delayed fluorescence and phosphorescence, with former one having the advantage. Here, an organic helical assembly supports it towards phosphorescence in this competitive pathway to exhibit an ultralong phosphorescence lifetime. In contrary to other molecules, 3,6-phenylmethanone functionalized 9-hexylcarbazole exhibits a remarkable improvement in phosphorescence lifetime (> 4.1 sec) and quantum yield (11 %) due to an efficient molecular packing in the crystal state. A right-handed helical molecular array act as a trap and exhibits triplet exciton migration to support the exceptionally longer phosphorescence lifetime. The present work will urge new molecular designs to achieve ultralong organic phosphorescence under ambient conditions.
关键词： ultralong phosphorescence,phenylmethanone,carbazole,waveguiding,helicity
更新于2025-09-23 15:21:01
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Portable Instrument for Monitoring Environmental Toxins Using Immobilized Quantum Dots as the Sensing Material
摘要： A portable instrumental system was designed for the routine environmental monitoring of toxic volatile organic compounds (VOCs) in atmospheric conditions based on changes in the photoluminescence emission of semiconductor nanoparticles (quantum dots) entrapped in a sol-gel matrix as the solid sensing material. The sol-gel sensing material displayed a long-lived phosphorescent emission, which is quenched in the presence of trace levels of a volatile organic compound (acetone) in gaseous atmospheres. The developed instrument could measure and process the changes in the photoluminescence of the sensing material after exposure to gaseous acetone. The developed prototype device consists of a deep-ultraviolet light-emitting diode (UV LED), which excites the chemical sensing material; an optical filter to remove scattered light and other non-desirable wavelengths; a photomultiplier tube (PMT) to convert the phosphorescence emission of the sensor phase to an electrical signal; and a microcontroller to correlate the signal with the analyte concentration. The developed prototype was evaluated for its ability to measure low levels of gaseous acetone in contaminated atmospheres with high sensitivity (detection limit: 9 ppm). The obtained results show the feasibility of this type of instrument for environmental analytical control purposes.
关键词： quantum dots (QDs),photomultiplier,UV LED,instrumentation,nanoparticles,room temperature phosphorescence (RTP)
更新于2025-09-23 15:21:01
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Heavy Atom Effect of Selenium for Metal-Free Phosphorescent Light-Emitting Diodes
摘要： Room-temperature phosphorescence from metal-free purely organic molecules has recently gained much interest. We devised metal-free organic phosphors by incorporating selenium (Se) to promote spin?orbit coupling by its nonmetal heavy atom effect. The Se-based organic phosphors showed bright phosphorescent emission in organic light-emitting diodes (OLEDs) and photo-excited phosphorescence in an amorphous film state. Large orbital angular momentum change (ΔL) during the electron transition process and heavy atom effect of Se render a PL quantum yield of 0.33 ± 0.01 and a high external quantum efficiency (EQE) of 10.7 ± 0.14% in phosphorescent LEDs. This work demonstrates the rational molecular design of metal-free organic phosphorescent emitters with Se as an alternative novel class of materials to the conventional organometallic phosphors for OLEDs.
关键词： organic light-emitting diodes,spin?orbit coupling,selenium,metal-free organic phosphors,phosphorescent LEDs,room-temperature phosphorescence
更新于2025-09-23 15:19:57
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Physicala??Chemical Properties of Self-Assembled Structures in Solution of Zinc Phthalocyanine and Bis-3-pentyl-PTCDI Derivative
摘要： For the first time, in this work, we succeed in synthesizing in solution a novel supramolecular self-assembled zinc phthalocyanine (ZnPc) and N,N′-bis(3-pentyl)-perylene-3,4,9,10-bis(dicarboximide) (bis-3-pentyl-PTCDI) system with improved light absorption and phosphorescence lifetime of the charge separated states up to 2.5 ms. Moreover, the structural and optical properties of undoped and doped with iodine ZnPc thin films were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman analysis, and UV?vis spectroscopy. Analysis of ZnPc:I2:bis-3-pentyl-PTCDI blend in a 2:1 ratio shows that sandwich complexes between them result in improved bulk properties as compared to those of the single-component systems.
关键词： light absorption,Fourier transform infrared spectroscopy,UV?vis spectroscopy,bis-3-pentyl-PTCDI,X-ray diffraction,supramolecular self-assembly,X-ray photoelectron spectroscopy,zinc phthalocyanine,phosphorescence lifetime,Raman analysis
更新于2025-09-23 15:19:57