Phosphorescence Lifetime Research Articles

Optical Methods for the Study of Brain Metabolism In Situ.

From its inception, the International Society of Oxygen Transport to Tissue (ISOTT) included several core members who were intrigued by the possibility of using light to probe the metabolic state of the cerebral cortex. This 50th anniversary review will focus on optical methods (UV, Visible, NIR) used to study brain oxygen metabolism in the intact brain. Chance, Lübbers, and Jöbsis did fundamental work in the 1970s and 1980s. These investigators spearheaded the use of fluorescence of pyridine nucleotides (e.g., NADH) and flavoprotein, and visible and near-infrared spectroscopy of haemoglobin amount and saturation, as well as the mitochondrial cytochrome chain. Two of our society awards are named for these pioneers and founders. By the new millennium, their many scientific descendants (although still too few for the task at hand) have been productive and moved the field forward. Technical advances in materials, detectors, devices, and computer power have made great advances possible. Physiological theory and understanding of cell and molecular mechanisms still lag, providing fertile territory for future goals. There are at least two major directions currently that will certainly continue to illuminate brain metabolism (obvious-and well worn-pun intended). These are the burgeoning NIR instrumentation variations, and second, the tremendous potential of two-photon phosphorescence lifetime microscopy. These advances have been introduced through the years and continue to be advanced at our annual ISOTT symposia.

Cluster-induced aggregation in polyurethane derivatives with multicolour emission and ultra-long organic room temperature phosphorescence

Cluster-induced aggregation, multicolour luminescence and ultra-long phosphorescence (0.45 s) in NCLPs based on polyurethane derivatives have been achieved by simply adjusting reaction temperature and reaction time; this is the longest reported phosphorescence lifetime for pure NCLPs.

Maximum-A-Posteriori Estimation of Retinal Oxygen Tension Based on Photon Counting Statistics.

The regularization of retinal oxygen tension estimation was previously proposed with an assumption that phosphorescence intensity images are corrupted by additive Gaussian noise. Based on this assumption, a regularized least-squares estimate has been shown to be better than a conventional least-squares estimation. However, this assumption is inconsistent with the acquisition process of phosphorescence intensity images acquired using an intensified charge-coupled device camera. Almost the entire acquisition process is governed by the natural aspects of photons. Therefore, a method based on photon counting statistics is more appropriate. In this study, we propose a regularized oxygen tension estimation method based on photon counting statistics and a phosphorescence lifetime imaging model.

Efficient triplet exciton phosphorescence quenching from a rhenium monolayer on silicon

Using phosphorescence lifetime image microscopy (PLIM) measurements we report up to 95% efficient triplet exciton energy transfer from a rhenium(i) fac-tricarbonyl bipyridine complex deposited as a Langmuir–Blodgett monolayer to crystalline silicon.

Oxygen Assessment in Tumors In Vivo Using Phosphorescence Lifetime Imaging Microscopy.

The oxygen level in a tumor is a crucial factor for its development and response to therapies. Phosphorescence lifetime imaging (PLIM) with the use of phosphorescent oxygen probes is a highly sensitive, noninvasive optical technique for the assessment of molecular oxygen in living cells and tissues. Here, we present a protocol for microscopic mapping of oxygen distribution in a mouse tumor model in vivo. We demonstrate that PLIM microscopy, in combination with an Ir(III)-based probe, enables visualization of cellular-level heterogeneity of tumor oxygenation.

Enhanced TNT vapor sensing through a PMMA-mediated AIPE-active monocyclometalated iridium(III) complex: a leap towards real-time monitoring.

Based on the explosive nature and harmful effects of nitro-based explosive materials on living beings and the environment, it is extremely important to develop luminescence-based probe molecules for their detection with excellent selectivity and sensitivity. Two AIPE (aggregation-induced phosphorescence emission)-active iridium(III) complexes (M1 and M2) were developed for the sensitive detection of TNT in both contact and non-contact modes. The aggregate solutions of both complexes (M1 and M2 in THF/H2O, 1/9 by volume) detected TNT at the pico-molar (pM) level. These complexes showed greatly enhanced emission intensity while embedded in a PMMA(polymethyl methacrylate) matrix film. The amplified quantum efficiency, improved phosphorescence lifetime, and enhanced porous network of M2-PMMA composite helps to improve the sesitivity of TNT vapor detection. Interestingly, the sensitivity of the detection of TNT by the M2 complex was significantly improved (5-fold) in a PMMA-incorporated complex (CP) with an observed limit of detection (LOD) of 12.8 ppb. From the BET analysis of CP, it was observed that the mesoporous network of CP has an average pore diameter of 8.52 nm and a surface area of 2.03 m2 g-1. The porous network of CP assists in trapping TNT vapor in a polymeric network containing an electron-rich probe (iridium(III) complex, M2), which helps to effectively trap TNT, thus enhancing electronic communication. As a result, significant emission quenching was observed.

Ultralong afterglow of heavy-atom-free carbon dots with a phosphorescence lifetime of up to 3.7 s for encryption and fingerprinting description.

Metal-free room-temperature phosphorescent (RTP) materials with changeable colors have attracted great attention in anti-counterfeiting information encryption. Most ultralong-lifetime RTP (URTP) luminophores are traditionally obtained through heavy atom effects via enhancing the spin-orbit coupling efficiency. Here, we report the self-assembly of URTP carbon dots (CDs) using diphenylaminourea as the precursor through a thermal-evaporation assisted covalent-binding approach in the presence of boric acid (BA). The BA-functionalized diphenylaminourea-derived CDs (denoted as D-CDs1.5/BA composites) show a rigid network structure with B-C linkages connected to the surface of the CDs, which can effectively suppress the free vibration of CDs to promote intersystem crossover, finally resulting in an excellent URTP afterglow performance. They feature a low singlet-triplet energy gap and reduced nonradiative attenuation properties. As a result, the D-CDs1.5/BA composites exhibit a bifunctional fluorescence/phosphorescence performance with a high phosphorescence quantum efficiency (12.67%) and an ultra-long green afterglow phosphorescence lifetime of up to 3.66 s. A high-level information encryption and fingerprinting description based on the URTP D-CDs1.5/BA composites were then investigated. This work contributes to the feasible design and preparation of novel URTP CD materials with both ultra-long afterglow and a high phosphorescence efficiency, making them promising candidates for advanced anti-counterfeiting applications.

Metal oxide hybridization enhances room temperature phosphorescence of carbon dots-SiO2 matrix for information encryption and anti-counterfeiting.

Room temperature phosphorescent (RTP) carbon dot (CD) materials have been widely used in various fields, but it is difficult to achieve a long lifetime, high stability and easy synthesis. In particular, realizing the phosphorescence emission of CDs using a metal oxide (MO) matrix is a challenge. Here, solid gels are synthesized via in situ hydrolysis, and then RTP CDs are synthesized based on a SiO2 matrix (CDs@SiO2) and hybridized with a MO matrix (CDs@SiO2-MO) by high-temperature calcination. Among the materials synthesized, Al2O3 matrix RTP CDs (CDs@SiO2-Al2O3) have a long phosphorescence lifetime of 689 ms and can exhibit yellow-green light visible to the naked eye for 9 s after the UV light (365 nm) is turned off. Compared with the green phosphorescence of CDs@SiO2, the yellow-green phosphorescence lifetime of CDs@SiO2-Al2O3 is enhanced by 420 ms. In addition, CDs@SiO2-Al2O3 maintains good stability of phosphorescence emission in water, strongly oxidizing solutions and organic solvents. As a result, CDs@SiO2-Al2O3 can be applied to the field of information encryption and security anti-counterfeiting, and this work provides a new, easy and efficient synthesis method for MO as an RTP CD matrix.

Dual luminescence and infrared circularly polarized luminescence up to 900 nm with platinum complexes bearing a helical donor-acceptor ligand.

Chiral molecular materials able to emit circularly polarized luminescence (CPL) have attracted considerable interest in the last few decades, due to the potential of CP-light in a wide range of applications. While CP luminescent molecules with blue, green, and yellow emissions are now well-reported, NIR CPL from organic and organometallic compounds lags behind due to the dual challenge of promoting radiative deexcitation of the excited state in this low energy region while assuring a significant magnetic dipole transition moment, a prerequisite for generating CPL. Based on a versatile axially chiral arylisoquinoline ligand, we report the synthesis and chiroptical properties of chiral donor-acceptor platinum(ii) complexes displaying CPL that extends up to almost 900 nm. Interestingly, these emitters show both fluorescence and phosphorescence emissions in solution, with intensities depending on the charge-transfer character of the organic ligand. Experimental and theoretical investigations show that this feature strongly impacts the intersystem crossing event between the singlet and triplet excited states of these complexes and the related phosphorescence lifetime. The effect is less important regarding the CPL, and most complexes show luminescence dissymmetry factors with values up to ca. 2 × 10-3 around 800 nm.

Construction and fine tuning of host-guest doping systems and the underlying mechanism of room temperature phosphorescence

To obtain ultralong and efficient pure organic room temperature phosphorescent materials, as well as explore the intrinsic mechanisms affecting the phosphorescence performance of host-guest doping systems, two carbazole derivatives with the same molecular structure, named as L-CzIPCN and CzIPCN, were prepared by using carbazole synthesized in the laboratory and commercial carbazole. By choosing L-CzIPCN/CzIPCN and polymethyl methacrylate (PMMA)/polyvinyl alcohol (PVA)/benzophenone derivatives (BP, F-BP, Br-BP, and DF-BP) as the guest and host respectively, a series of new doping systems were constructed, and optimized by tuning doping ratios between host and guest materials. Among of them, F-BP/L-CzIPCN shows the longest room temperature phosphorescence (RTP) lifetime (501.23 ms), with RTP quantum yield of 31.19 %, followed by 0.2 % L-CzIPCN@PVA film (221.66 ms, 5.86 %) and 0.2 % L-CzIPCN@PMMA film (102.73 ms, 4.28 %) respectively. Moreover, L-CzIPCN displays different RTP spectra in diverse hosts, with dual-band RTP emission at 550 nm and 600 nm in benzophenone derivatives, but single RTP emission maxima in PMMA films, as well as a main emission peak at 470–510 nm and a shoulder peak at 550–590 nm in PVA films. The UV–Vis absorption spectra, fluorescence and phosphorescence spectra, and theoretical calculations indicate that RTP comes from the guest monomers in benzophenone derivatives/L-CzIPCN doping systems, with local triple characteristics, and host materials with large dipole moment, appropriate T1 energy level, and small energy gap between S1 and T1 contribute to improving RTP performance of the doping systems. Based on the excellent luminescence and different RTP lifetimes of the doping systems, some high-level anti-counterfeiting, and information encryption patterns were successfully constructed.

Fused-Ring Pyrrole-Based Near-Infrared Emissive Organic RTP Material for Persistent Afterglow Bioimaging.

Organic near-infrared room temperature phosphorescence (RTP) materials offer remarkable advantages in bioimaging due to their characteristic time scales and background noise elimination. However, developing near-infrared RTP materials for deep tissue imaging still faces challenges since the small band gap may increase the non-radiative decay, resulting in weak emission and short phosphorescence lifetime. In this study, fused-ring pyrrole-based structures were employed as the guest molecules for the construction of long wavelength emissive RTP materials. Compared to the decrease of the singlet energy level, the triplet energy level showed a more effectively decrease with the increase of the conjugation of the substituent groups. Moreover, the sufficient conjugation of fused ring structures in the guest molecule suppresses the non-radiative decay of triplet excitons. Therefore, a near-infrared RTP material (764 nm) was achieved for deep penetration bioimaging. Tumor cell membrane is used to coat RTP nanoparticles (NPs) to avoid decreasing the RTP performance compared to traditional coating by amphiphilic surfactants. RTP NPs with tumor-targeting properties show favorable phosphorescent properties, superior stability, and excellent biocompatibility. These NPs are applied for time-resolved luminescence imaging to eliminate background interference with excellent tissue penetration. This study provides a practical solution to prepare long-wavelength and long-lifetime organic RTP materials and their applications in bioimaging.

Fused‐Ring Pyrrole‐Based Near‐Infrared Emissive Organic RTP Material for Persistent Afterglow Bioimaging

AbstractOrganic near‐infrared room temperature phosphorescence (RTP) materials offer remarkable advantages in bioimaging due to their characteristic time scales and background noise elimination. However, developing near‐infrared RTP materials for deep tissue imaging still faces challenges since the small band gap may increase the non‐radiative decay, resulting in weak emission and short phosphorescence lifetime. In this study, fused‐ring pyrrole‐based structures were employed as the guest molecules for the construction of long wavelength emissive RTP materials. Compared to the decrease of the singlet energy level, the triplet energy level showed a more effectively decrease with the increase of the conjugation of the substituent groups. Moreover, the sufficient conjugation of fused ring structures in the guest molecule suppresses the non‐radiative decay of triplet excitons. Therefore, a near‐infrared RTP material (764 nm) was achieved for deep penetration bioimaging. Tumor cell membrane is used to coat RTP nanoparticles (NPs) to avoid decreasing the RTP performance compared to traditional coating by amphiphilic surfactants. RTP NPs with tumor‐targeting properties show favorable phosphorescent properties, superior stability, and excellent biocompatibility. These NPs are applied for time‐resolved luminescence imaging to eliminate background interference with excellent tissue penetration. This study provides a practical solution to prepare long‐wavelength and long‐lifetime organic RTP materials and their applications in bioimaging.

Optimization of Transcutaneous Oxygenation Wearable Sensors for Clinical Applications

AbstractIn this manuscript, the development of an experimental and mathematical toolset is reported that allows for improved in vivo measurements of optical transcutaneous oxygen tension measurements (TCOM) wearable technology in humans. In addition to optimizing O2‐sensing films for higher sensitivity oxygen detection, calibration algorithms are additionally developed to account for excitation source leakage, as well as algorithms to combine readings of partial pressure of oxygen (pO2), derived from phosphorescence intensity and lifetime, into a single metric. This new iteration of the TCOM wearable device is then tested in a pilot human study. By implementing characterization and calibration algorithms, the data from the pilot study demonstrates the ability to obtain reliable transcutaneous pO2 readings with a TCOM sensor regardless of size and without the need for strict conditions of constant temperature, humidity, or motion that have limited the range of applications of this technology in the past.

Monitoring the Intracellular pH and Metabolic State of Cancer Cells in Response to Chemotherapy Using a Combination of Phosphorescence Lifetime Imaging Microscopy and Fluorescence Lifetime Imaging Microscopy.

The extracellular matrix (ECM), in which collagen is the most abundant protein, impacts many aspects of tumor physiology, including cellular metabolism and intracellular pH (pHi), as well as the efficacy of chemotherapy. Meanwhile, the role of collagen in differential cell responses to treatment within heterogeneous tumor environments remains poorly investigated. In the present study, we simultaneously monitored the changes in pHi and metabolism in living colorectal cancer cells in vitro upon treatment with a chemotherapeutic combination, FOLFOX (5-fluorouracil, oxaliplatin and leucovorin). The pHi was followed using the new pH-sensitive probe BC-Ga-Ir, working in the mode of phosphorescence lifetime imaging (PLIM), and metabolism was assessed from the autofluorescence of the metabolic cofactor NAD(P)H using fluorescence lifetime imaging (FLIM) with a two-photon laser scanning microscope. To model the ECM, 3D collagen-based hydrogels were used, and comparisons with conventional monolayer cells were made. It was found that FOLFOX treatment caused an early temporal intracellular acidification (reduction in pHi), followed by a shift to more alkaline values, and changed cellular metabolism to a more oxidative state. The presence of unstructured collagen markedly reduced the cytotoxic effects of FOLFOX, and delayed and diminished the pHi and metabolic responses. These results support the observation that collagen is a factor in the heterogeneous response of cancer cells to chemotherapy and a powerful regulator of their metabolic behavior.

Photophysical characteristics of C60-threoninen (n = 1–4) complexes: DFT study

DFT calculations showed that disruption of the π network of the fullerene due to the addition of up to four threonines does not affect the efficiency of saturation of the T1 state by intersystem crossing compared to pure C60. Internal conversion from S1 to the ground state does not compete with intersystem crossing to T1 state. The regulating of C-H vibrations associated with hydrogens bound to fullerene may govern the quantum yield of the triplet state saturation. Resulting phosphorescence lifetimes high enough to guarantee a high probability of quenching the triplet state by molecular oxygen.

Triplet Exciton Harvesting in Water by a Structurally Simple Organic Phosphor with Sustained Afterglow and Lifetime Tunability

AbstractUltra‐long room temperature phosphorescence (URTP) materials are extremely promising for applications in organic electronics. Creating materials with controlled photophysics to achieve this, however, is difficult due to the challenges in filling up and stabilizing the sensitive triplet excited states at ambient temperature. Herein, triplet excitons are harvested by an intuitively designed structurally simple organic phosphor in water under ambient conditions by using supramolecular host–guest chemistry with cucurbituril‐7 (CB7) and sodium dodecyl sulphate (SDS), a negatively charged surfactant, with high photoluminescence (PL) quantum yields (PLQYs) (69% and 73% for CB7 and SDS, respectively) and phosphorescence lifetimes (12.52 and 12.42 ms for CB7 and SDS, respectively). A protective polyvinyl alcohol (PVA) film successfully controls the afterglow emission, excited state lifetime as well as PLQY in a single organic phosphor (CzPy24+). While a 1% concentration of CzPy24+ in the PVA film shows blue phosphorescence with 78.82% PLQY having a lifetime of 1.9 s, a 5% of CzPy24+ addition shows a green afterglow with 67.52% PLQY and a lifetime of 1.3 s. Similarly, yellow afterglow is achieved on adding 20% CzPy24+ to the PVA film with a PLQY of 40.88%. The findings are promising and helpful in constructing tunable phosphors for suitable applications.

Promoting intersystem crossing by charge transfer state of dimers for persistent room temperature phosphorescence

Efficient intersystem crossing (ISC) is essential for phosphorescence emission. The charge transfer (CT) state is traditionally constructed by highly twisted donor-acceptor type structures to facilitate the ISC process. However, the highly twisted structural properties limit the diversity of room-temperature phosphorescence (RTP) molecules. By establishing the CT state in the intermolecular dimers structure, the dependence on the distorted donor-acceptor in the single-molecule design can be well eliminated. Based on this strategy, three novel pure organic luminescent molecules with long afterglow and mechanochromic luminescence (MCL) property were designed and synthesized. All of those exhibited triple emission, including prompt fluorescence (PF), delayed fluorescence (DF) and persistent RTP (pRTP) emission. In particular, CzC4-PhCN showed great potential for application in the field of anti-counterfeiting with its ultralong phosphorescent lifetime of 862 ms. Single crystal analysis and theoretical calculation revealed that the formation of CT states of intermolecular dimers effectively reduced ΔEST and promoted ISC process. This study would be highly instructive for realizing efficient ISC process and high-efficiency pRTP emission in pure organic systems.

Unique Visualization Growth Process of Long-Lived Room Temperature Phosphorescence in Polymer System.

Recently, embedding organic phosphors into the polyvinyl alcohol (PVA) matrix has emerged as a convenient strategy to obtain efficient long-lived room temperature phosphorescence (RTP) via forming strong intermolecular hydrogen bonds with organic phosphors to minimize nonradiative relaxations. Regrettably, it is discovered that PVA is unable to trigger RTP emission when a novel functional phosphor THBE containing six extended biphenyl formaldehyde arms is doped into PVA matrix. Surprisingly, the excellent long-lived RTP emission can be easily obtained by doping THBE into PVA analogs, poly(vinyl alcohol-co-ethylene) (PVA-co-PE). The unique visualization growth process (i.e., white streak generation) of long-lived RTP is observed by UV light-driven aggregation of functional molecules THBE in PVA-co-PE matrix. The phosphorescent intensity of the luminescent film is enhanced by 55 times, from 729 to 40,785 a.u., and its phosphorescence lifetime is increased by 38 times, from 37.08 to 1415.41ms. Due to the dynamically reversible RTP performance, as well as the permeability, flexibility, and wrinkle-free properties of the luminescent film, it can be utilized to create cutting-edge information storage devices.

Achieving tunable long persistent luminescence in metal organic halides based on pyridine solvent

The research of long persistent luminescence (LPL) materials has yield brilliant results in many fields. However, the efforts are still needed for the regulation of the LPL performance. In this work, a series of LPL metal organic halides with rich halogen-bond interactions, Py-CdX2 (X = Cl, Br, I) were synthesized through self-assembly by CdX2 and pyridine solvent. The steady-state emission redshifted and phosphorescence lifetime declined as the halogen atoms are aggravated. Three halides exhibit adjustable emission from blue to green and multiple phosphorescence from green to yellow at room temperature by changing the excitation wavelengths. Surprisingly, Py-CdX2 can emit the visible color-tunable LPL from green to yellow after removing different excitation sources at ambient conditions. Combing the results of theoretical calculation and experimental analysis, it is found that heavy atom effect and the rich intermolecular halogen bond help realize LPL and multiple triplet states originated from the pyridine ring and the halogens.

Chiral‐Guest Induced Multicolor‐Tunable Circularly Polarized Room Temperature Phosphorescence

AbstractThe development of organic circularly polarized room temperature phosphorescence (CP‐RTP) materials with tunable emission colors has important value in the field of optoelectronic applications but remains a challenging issue. Herein, a CP‐RTP doped system with green, yellow, and red afterglow is constructed by introducing chiral groups into three phosphors naphthalene, phenanthrene, and pyrene as guests respectively, using polyvinyl pyrrolidone (PVP) as the host. The phosphorescence quantum yield of the doped system is 7.3%–13.6%, the phosphorescence lifetime is 341 ms–1017 ms, and the asymmetry factor is 0.001–0.0021. Further doping three guests simultaneously into the PVP resulted in the four‐component doped materials. Benefiting from the different excitation wavelengths of three guests, when the excitation wavelength changes from 300 to 365 nm, the afterglow of the four‐component doped materials changes from green to yellow and finally to red. Moreover, due to the different phosphorescence lifetimes of different guests, the afterglow can in turn change from red to green after excitation at 365 nm, demonstrating a time‐dependence phosphorescence emission property. This doped strategy provides an effective platform for constructing organic multicolor CP‐RTP materials.