Heavy atom induced room temperature phosphorescence: a tool for the analytical characterization of polycyclic aromatic hydrocarbons

A Ground-State Dual-Descriptor Strategy for Screening Efficient Singlet Fission Systems

Exploration of singlet fission (SF) materials is vital for enhancing the photoelectric conversion efficiency of photovoltaic devices, and the development of an effective screening means is in great demand. In this work, we for the first time propose a promising dual-descriptor strategy to predict the SF energetics (ΔESF) from ground-state electronic properties, the gap (GapHL) and exchange energy (KHL) between the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO), where GapHL plays a dominant role and KHL acts as a correction. This strategy is statistically verified through exploring the effect of N-doping on the electronic/energetic properties of the N-doped tetracene derivatives and isomers. Several rules of thumb are suggested, and the reliability of this strategy is validated by comparison with experiments. This work proposes a novel strategy for exploring SF chromophores with insights into the SF energetics from ground-state properties and certainly has fundamental interest and generality in exploring efficient SF-capable materials.

Stacked nanocarbon photosensitizer for efficient blue light excited Eu(III) emission

Photosensitizer design to allow effective use of low-energy light is important for developing photofunctional materials. Herein, we describe a rational photosensitizer design for effective use of low-energy light. The developed photosensitizer is a stacked nanocarbon based on a rigid polyaromatic framework, which allows efficient energy transfer from the low-energy T₁ level to the energy acceptor. We prepared an Eu(III) complex consisting of a luminescent center (Eu(III)) and stacked-coronene photosensitizer. The brightness of photosensitized Eu(III) excited using low-energy light (450 nm) is more than five times higher than the maximum brightness of previously reported Eu(III) complexes.

Room temperature phosphorescence of five PAHs in a synergistic mesoporous silica nanoparticle-deoxycholate substrate

A synergistic mesoporous silica nanoparticle-sodium deoxycholate (mPS-NaDC) substrate was developed for room temperature phosphorimetry. The synergistic substrate exhibited rapid and strong RTP-inducing ability against temperature variation. NaDC might adsorb on the inner surface of mPS pore by possible hydrogen bonding and protected the triplet state of polycyclic aromatic hydrocarbons (PAHs) with different molecular sizes. Two mPSs named LPMS1 and LPMS2 with pore size of 3.05 and 3.83nm were synthesized and optimized in inducing RTP, and the latter, LPMS2, was selected as an ideal substrate because of its stronger protection ability to the triplet and good stability. Dibromopropane and cyclohexane were also used as assistant phosphorescence-inducers. All results demonstrated the feasibility and application potential of synergistic mPS-NaDC substrate in phosphorimetry. The interaction detail of NaDC and inner surface of selected mPS still needs to be explored in future.

Interactions between haloperfluorobenzenes and fluoranthene in luminescent cocrystals from π-hole⋯π to σ-hole⋯π bonds

From π-hole⋯π to σ-hole⋯π bonds between haloperfluorobenzenes and fluoranthene in luminescent cocrystals.

Crystal induced phosphorescence from Benz(a)anthracene microcrystals at room temperature

Pure organic compounds that are also phosphorescent at room temperature are very rare in literature. Here, we report efficient phosphorescence emission from aggregated hydrosol of Benz(a)anthracene (BaA) at room temperature. Aggregated hydrosol of BaA has been synthesized by re-precipitation method and SDS is used as morphology directing agent. Morphology of the particles is characterized using optical and scanning electronic microcopy (SEM). Photophysical properties of the aggregated hydrosol are carried out using UV-vis, steady state and time resolved fluorescence study. The large stoke shifted structured emission from aggregated hydrosol of BaA has been explained due to phosphorescence emission of BaA at room temperature. In the crystalline state, the restricted intermolecular motions (RIM) such as rotations and vibrations are activated by crystal lattice. This rigidification effect makes the chromophore phosphorescent at room temperature. The possible stacking arrangement of the neighboring BaA within the aggregates has been substantiated by computing second order Fukui parameter as local reactivity descriptors. Computational study also reveals that the neighboring BaA molecules are present in parallel slipped conformation in its aggregated crystalline form.

Pre-denaturing transitions in human serum albumin probed using time-resolved phosphorescence

The investigation of protein dynamics has long been of interest, since protein interactions and functions can be determined by their structure and changes in conformation. Although fluorescence, occurring on the nanosecond timescale, from intrinsic fluorescent amino acids has been extensively used, in order to fully access conformational changes longer timescales are required. Phosphorescence enables processes on the microsecond to second timescale to be accessed. However, at room temperature this emission can be weak and non trivial to measure. It requires the removal of oxygen - a common triplet state quencher and appropriate instrumentation. In this work we make use of a chemical deoxygenator to study room temperature phosphorescence from tryptophan in human serum albumin excited using a pulsed UV light emitting diode. This is extended to monitor the phosphorescence emission upon increasing temperature, allowing pre-denaturing transitions to be observed. Time-resolved data are analysed, both as the sum of exponential decays and using a distribution analysis based on non extensive decay kinetics. These results are compared to a fluorescence study and both the average lifetime and contribution of the different emitting components were found to give more dramatic changes on the phosphorescence timescale.

Phosphate-containing metabolites switch on phosphorescence of ferric ion engineered carbon dots in aqueous solution

Room temperature phosphorescence of carbon dots readily engineered by ferric ions in aqueous solution was developed for a novel “off-to-on” approach for cost-effective estimation of ATP level in human blood plasma.

Room temperature phosphorescence of 9-bromophenanthrene, and the interaction with various metal ions

The Flow Inject Drop Luminescence Sensor (FIDLS) is featured by advantages such as high precision and work simplification over typical luminescent spectrometers. With the FIDLS system, this study is the first to examine the sodium deoxycholate (NaDC) inducing room temperature phosphorescence (RTP) of 9-bromophenanthrene (BrP). Among the factors that influenced phosphorescence, the injection speed of the FIDLS was optimized at 5.0 mL h(-1). A solvent content of 1.0% or less was selected to avoid RTP quenching. When samples were placed at temperatures higher than room temperature (e.g., 303 K), the standing time of the sample decreased. The minimum detectable level of BrP was 8.0 × 10(-10) mol L(-1), and BrP RTP reached its maximum intensity at a BrP concentration of 1.0 × 10(-5) mol L(-1). The optimal clathrate concentration of NaDC was 4.9 × 10(-3) mol L(-1), which was also the critical micelle concentration. We found that NaDC primary micelles gradually formed, but that secondary micelles formed and decomposed at a considerably faster rate. Fluorescence and absorbance tests demonstrated the coordination reactions of BrP with Cr(6+) and Fe(3+), indicating the potential application of BrP as a fluorescence probe.

Body- or tip-controlled reactivity of gold nanorods and their conversion to particles through other anisotropic structures

We report the shape transformation of gold nanorods to spherical nanoparticles, assisted by cupric ions. The reaction proceeds through a series of structures and could be arrested at any stage to produce particles of desired shape. In the presence of a larger concentration of cetyltrimethylammonium bromide (CTAB), selective etching of the tips of the nanorods occurs to a greater extent. The subsequent transformation is driven by the surface reconstruction of nanorods to generate more stable surfaces. As the stability of various surfaces depends on the protecting agent used, the reactivity is modified by controlling its presence at the surface. We show that the body of the rods is more susceptible for reaction at reduced CTAB concentrations. During the conversion to particles, several anisotropic transient structures were observed and were imaged using high-resolution transmission electron microscopy (HRTEM). The transformation occurs due to the hydroxyl radicals produced by Cu2+ in the presence of ascorbic acid (AA). A mechanism has been proposed and several control experiments were conducted to test it. The cupric ion induced shape transformations can be extended to other ions, and knowing the mechanism allows the control of the process to stabilize various anisotropic structures.

Room-temperature excitation–emission phosphorescence matrices and second-order multivariate calibration for the simultaneous determination of pyrene and benzo[a]pyrene

The present article describes the simultaneous phosphorimetric determination of pyrene and benzo[a]pyrene, two highly toxic polycyclic aromatic hydrocarbons, through excitation-emission phosphorescence matrices (EEPMs) and second-order calibration. The developed approach enabled us to determine both compounds at microg L(-1) concentration levels without the necessity of applying separation steps, as well as significantly reducing the experimental time. An artificial neural network (ANN) approach was applied to optimize the chemical variables which have an influence on the room-temperature phosphorescence emission of the studied analytes. The present study was employed for the discussion of the scopes of the applied second-order chemometric tools: parallel factor analysis (PARAFAC) and partial least-squares with residual bilinearization (PLS/RBL). The superior capability of PLS/RBL to model the profiles of other potentially interferent polycyclic aromatic hydrocarbons (PAHs) was demonstrated. The quality of the proposed method was established with the determination of both pyrene and benzo[a]pyrene in artificial and real water samples.

Study of the heavy atom-induced room temperature phosphorescence properties of melatonin and its analytical application

Liquid phase room temperature phosphorescence (RTP) properties of melatonin were studied using heavy atom induced-room temperature phosphorescence (HAI-RTP) technique. 1.2 M potassium iodide was used as a heavy atom reagent together with 0.002 M sodium sulphite as deoxygenating agent to produce the RTP signal. The maximum phosphorescence emission and excitation wavelengths of melatonin were 290 and 457 nm, respectively. The effect of potassium iodide concentration on the RTP lifetime of melatonin was also investigated and based on the results, the rate constants for phosphorescence decay (k(p)) and radiationless deactivation through reaction with heavy atom (k(h)) were determined. Based on the obtained results, a simple and sensitive room temperature phosphorimetric method was developed for the determination of melatonin. The method allowed the determination of 10.0-200 ng ml(-1) melatonin in aqueous solution with the limits of detection and quantification of 3.6 and 12 ng ml(-1), respectively. The proposed method was satisfactorily applied to the determination of melatonin in commercial pharmaceutical formulations.

Pyrene–p-tert-butylcalixarenes inclusion complexes formation: a surface photochemistry study

Diffuse reflectance and luminescence techniques were used to study the photophysics and photochemistry of pyrene within p-tert-butylcalix[n]arenes with n = 4, 6, and 8, and to study their ability to form inclusion complexes in heterogeneous media. Evidences for inclusion complex formation were found for the three hosts under study. Ground state diffuse reflectance results have shown the formation of ground state dimers of pyrene inside the cavity of calix[6]arene and calix[8]arene, with this feature much more evident for calix[6]arene. For calix[4]arene, only a monomer fits inside the cavity and the presence of pyrene microcrystals outside the cavity was detected. A luminescence lifetime distribution analysis was performed, revealing the presence of prompt emissions from the pyrene microcrystals outside the cavity in the case of calix[4]arene and from the constrained dimers inside the cavities of calix[6]arene and calix[8]arene. Transient absorption results have shown the presence of pyrene radical cation and also of trapped electrons for the three hosts under study. The formation of the phenoxyl radical of the calixarene following the laser pulsed excitation of pyrene at 355 nm is increased for calix[6]arene and calix[8]arene. This feature is particularly relevant for calix[6]arene, suggesting a very favourable situation for the hydrogen atom abstraction to occur. The analysis of the degradation products revealed the presence of hydroxypyrene as a major photodegradation product for the three hosts. Dihydro-hydroxypyrene was also formed in the case of calix[6]arene and calix[8]arene. The formation of the calixarene's phenoxyl radical and subsequent hydrogen abstraction is consistent with the formation of dihydro-dihydroxypyrene.

Molecularly Imprinted Polymers Based on Iodinated Monomers for Selective Room-Temperature Phosphorescence Optosensing of Fluoranthene in Water

Aiming at enhancing the advantages of traditional molecularly imprinted polymers (MIPs) for chemical sensing, a new MIP design approach introducing an internal heavy atom in their polymeric structure is described. Based on the heavy-atom effect, the novel polymer allows one to perform room-temperature phosphorescence (RTP) transduction of the analyte. The synergic combination of a tailor-made MIP recognition with a selective RTP detection is a novel concept for optosensing devices which is assessed here for simple and highly selective determination of trace amounts of fluoranthene in water. The noncovalent MIP was synthesized using the laboratory-synthesized tetraiodobisphenol A as one of the polymeric precursors and fluoranthene as template. In the presence of an oxygen scavenger, the iodide included in the polymeric structure induced efficient RTP emission from the analyte, once recognized by the MIP. The developed optosensing system has demonstrated a high specificity for fluoranthene against other polycyclic aromatic hydrocarbons. Detection limit for the target molecule was 35 ng/L (5-mL sample injections), and the linear range extended above 100 microg/L of the analyte. The polymer can be easily regenerated for subsequent sample injections (at least up to 450 cycles) with acetonitrile. The synthesized sensing material showed good stability for at least 6 months after preparation. The feasibility of monitoring fluoranthene in real samples was successfully evaluated through the analysis of five spiked river water samples.

Effect of cyclic third components on non-deoxygenated RTP and their potential in developing optical thermometer

Effect of five cyclic third components, cyclohexane, methylcyclohexane, perfluorocyclohexane, perfluoromethylcyclohexane and adamantane, on cyclodextrin-induced room-temperature phosphorescence (CD-RTP) of 1-bromonaphthalene is studied. It is found that these five compounds can induce intensive RTP, and the enhancement order is as follows: cyclohexane>adamantane>methylcyclohexane>perfluorocyclohexane>perfluoromethylcyclohexane. Dependence of RTP intensity on temperature of these systems shows the potential application in developing optical thermometer.

Simple determination of the herbicide napropamide in water and soil samples by room temperature phosphorescence

A new, simple, rapid and selective phosphorimetric method for determining napropamide is proposed which demonstrates the applicability of heavy-atom-induced room-temperature phosphorescence for analyzing pesticides in real samples. The phosphorescence signals are a consequence of intermolecular protection and are found exclusively with analytes in the presence of heavy atom salts. Sodium sulfite was used as an oxygen scavenger to minimize room-temperature phosphorescence quenching. The determination was performed in 1 M potassium iodide and 6 mM sodium sulfite at 20 degrees C. The phosphorescence intensity was measured at 520 nm with excitation at 290 nm. Phosphorescence was easily developed, with a linear relation to concentration between 3.2 and 600.0 ng ml(-1) and a detection limit of 3.2 ng ml(-1). The method has been successfully applied to the analysis of napropamide in water and soil samples and an exhaustive interference study was also carried out to display the selectivity of the proposed method.

Iodinated molecularly imprinted polymer for room temperature phosphorescence optosensing of fluoranthene

A novel molecularly imprinted polymer (MIP) of high interest for room temperature phosphorescence (RTP) sensing systems is described; the synthesized MIP contains iodine as internal heavy atom in the polymeric structure and its applicability for RTP sensing of fluoranthene at microg L(-1) levels is demonstrated.