Time-resolved Fluorescence Spectroscopy Research Articles

Non-invasive thermal sensing and improved recoverable energy storage density of Bi0.5Na0.5TiO3: Er3+ doped multifunctional ferroelectric ceramic

In this work, Er3+ substituted bismuth sodium titanate ceramics with the chemical composition Bi0.5-xErxNa0.5TiO3 (x = 0.00, 0.01, 0.02, 0.03, 0.04, and 0.05) were synthesized using conventional solid state technique. The influence of Er3+ ions on structural, optical, ferroelectric, and temperature sensing properties have been investigated. The prepared ceramic powders were initially heated at a calcination temperature 850 °C to form single phase Bi0.5-xErxNa0.5TiO3 and finally sintered at temperature 1050 °C. Formation of pure phase compositions with rhombohedral crystal structure is confirmed through X-ray diffraction studies. The typical FTIR bands near 540, 860, 910 cm−1 confirmed the presence of Ti–O stretching of octahedral groups in the perovskite structure. The decent squared shaped saturated P-E hysteresis are obtained under an electric field of 60 ≤ E ≤ 70 kV/cm, and the loops become slimmer at higher Er3+ concentrations (x = 0.04). The efficiency of energy storage density increases with Er3+ doping and an improved recoverable energy storage (Wr = 2.73 J/cm3) and a higher efficiency (η = 70.77%) are obtained for Er content, x = 0.04. The photoluminescence spectra were recorded at two excitation wavelengths (488 nm and 980 nm). Two distinct green emission bands (529 nm and 550 nm) and one weak red emission band (670 nm) were observed at both excitation wavelengths. Increasing Er3+ content beyond (x > 0.03) leads to significant quenching of light emission due to cross relaxation process and non-radiative relaxations. The pump power dependency revealed that two photons were involved in the light upconversion process. The time-resolved fluorescence spectroscopy confirmed the decrease in lifetime with increasing Er3+ concentration. The absolute and relative sensitivity of the prepared ceramic at Er3+ concentration (x = 0.03) were found to be 0.47% K−1 at 523 K and 1.1% K−1 at 303 K, respectively. These optical and electrical properties open the possibility of realizing multifunctionality in the field of energy storage and opto-electronic applications.

Time-Resolved Fluorescence Spectroscopy of Blood, Plasma and Albumin as a Potential Diagnostic Tool for Acute Inflammation in COVID-19 Pneumonia Patients.

Fluorescence lifetime measurements of blood or plasma offer valuable insights into the microenvironment and molecular interactions of fluorophores, particularly concerning albumin. Neutrophil- and hypoxia-induced oxidative stress in COVID-19 pneumonia patients leads to hyperinflammation, various oxidative modifications of blood proteins, and potential alterations in the fluorescence lifetime of tryptophan-containing proteins, especially albumin. The objective of this study was to investigate the efficacy of time-resolved fluorescence spectroscopy of blood and plasma as a prompt diagnostic tool for the early diagnosis and severity assessment of COVID-19-associated pneumonia. This study examined a cohort of sixty COVID-19 patients with respiratory symptoms. To investigate whether oxidative stress is the underlying cause of the change in fluorescence lifetime, human serum albumin was treated with chloramine T. The time-resolved spectrometer Life Spec II (Edinburgh Instruments Ltd., Livingston, UK), equipped with a sub-nanosecond pulsed 280 nm diode, was used to measure the fluorescence lifetime of blood and plasma. The findings revealed a significant reduction in the fluorescence lifetime of blood (diluted 200 times) and plasma (diluted 20 times) at 360 nm in COVID-19 pneumonia patients compared with their respective values recorded six months post-infection and those of healthy individuals. Significant negative correlations were observed between the mean fluorescence lifetime of blood and plasma at 360 nm and several severity biomarkers and advanced oxidation protein products, while a positive correlation was found with albumin and the albumin-globulin ratio. The time-resolved fluorescence spectroscopy method demonstrates the potential to be used as a preliminary screening technique for identifying patients who are at risk of developing severe complications. Furthermore, the small amount of blood required for the measurements has the potential to enable a rapid fingerstick blood test.

Studies on <i>in vitro</i> binding of parecoxib to p38MAPK using spectroscopic methods

Purpose: To investigate the interaction between parecoxib and p38MAPK under simulated physiological conditions.Methods: The interaction between parecoxib and p38MAPK was studied under simulated physiological conditions using spectroscopy-based methods. The effect of parecoxib on the microenvironment and conformation of p38MAPK chromophore was studied by synchronous fluorescence spectroscopy, three-dimensional fluorescence, time-resolved fluorescence spectroscopy, circular dichroism spectroscopy, and ultraviolet-visible absorption spectroscopy.Results: Synchronous fluorescence spectroscopy showed that addition of parecoxib changed the structure of p38MAPK and destroyed the original stable structure. Three-dimensional fluorescence spectroscopy showed that the hydrophilicity of the microenvironment in which the fluorescent chromophore is located was enhanced, and the polarity increased such that the serum protein macromolecules tend to be unfolded, and the alpha-helix content reduced. Time-resolved fluorescence spectroscopy showed that the presence of parecoxib hardly affected the fluorescence quenching of p38MAPK, and the combination of parecoxib and p38MAPK forms a stable complex (static quenching). Circular dichroism spectroscopy revealed the combined parecoxib change, the secondary structure of p38MAPK and reduced the alpha-helix content. Ultraviolet-visible absorption spectroscopy revealed changes in the microenvironment of the three amino acid residues as well as the tertiary structure of the protein.Conclusion: The results shows that parecoxib has a significant effect on the structure of p38MAPK. In addition to explicitly inhibiting COX-2 and blocking arachidonic acid synthesis of prostaglandins, it inhibits the pathway involved in p38MAPK.

The Solvent-Dependent Photophysics of Diphenyloctatetraene.

Despite many decades of study, the excited state photophysics of polyenes remains controversial. In diphenylpolyenes with conjugated backbones that contain between 2 and 4 double carbon-carbon bonds, the first two excited electronic states are nearly degenerate but of entirely different character, and their energy splitting is strongly dependent on solvent polarizability. To examine the interplay between these different states, steady-state and time-resolved fluorescence spectroscopies were used to undertake a comprehensive investigation of diphenylocatetraene's (DPO) excited state dynamics in 10 solvents of different polarizabilities and polarities, ranging from weakly interacting alkanes to polar hydrogen-bonding alcohols. These data revealed that photopreparation of the optically bright 1Bu state resulted in fast (<170 ps) internal conversion to the lower-lying optically dark 2Ag state. The 2Ag state is responsible for almost all the observed DPO fluorescence and gains oscillator strength via vibronic intensity stealing with the near-degenerate 1Bu state. The fluorescence lifetime associated with the 2Ag state decayed monoexponentially (4.2-7.2 ns) in contrast to prior biexponential decay kinetics reported for similar polyenes, diphenylbutadiene and diphenylhexatriene. An analysis combining the measured fluorescence lifetimes and fluorescence quantum yields (the latter varying between 7 and 21%) allowed for a 190 cm-1 Herzberg-Teller vibronic coupling constant between the 1Bu and 2Ag states to be determined. The analysis also revealed that the ordering of electronic states remains constant in all the solvents studied, with the 2Ag state minimum always lower in energy than that of the 1Bu state, thus making it a relatively simple polyene compared to structurally similar diphenylhexatriene.

Probing the interaction and aggregation of lysozyme in presence of organophosphate pesticides: a comprehensive spectroscopic, calorimetric, and in-silico investigation

Organophosphorus pesticides (OPs) are widely used in agriculture and may contaminate food or water, leading to potential health risks. However, there are few reports on the effect of OPs on protein conformation and aggregation. Hence, in this paper, we have characterized the impact of two OPs, chlorpyrifos (CPF) and methyl parathion (Para), on the model protein HEWL using biophysical and computational methods. The steady-state and time-resolved spectroscopy, Circular dichroism (CD), molecular dynamics simulation, and isothermal titration calorimetry were employed to investigate the binding interactions between HEWL and OPs. The steady-state and time-resolved fluorescence spectroscopy confirm the presence of both static and dynamic quenching between OPs and proteins. Based on fluorescence, MD, and CD results, it was found that the OPs not only show strong binding but also destabilize the protein structure and alter the secondary and tertiary structure of the protein. The molecular docking results showed that OPs entered the binding pocket of the HEWL molecule and interacted through hydrophobic and hydrogen bond interactions. The thermodynamic studies indicated that the binding was spontaneous and OPs have shown an effect on the aggregation process of HEWL. Finally, the protein aggregation process was studied using fluorescence and SDS-PAGE studies in the presence of both the OPs and found to enhance the aggregation process in the presence of OPs. These results provide insights into the potential health risks associated with OPs and highlight the importance of understanding their interactions with biological macromolecules. Communicated by Ramaswamy H. Sarma

Repurposing the Strontium Ranelate Antiosteoporotic Drug as a New Outstanding Biocompatible Blue Dye

Blue dyes are relatively uncommon in nature, and a novel dithiophene dye (RanB) is reported in this paper. This dye is derived from an old anti-osteoporotic drug and is a metal ion complexing agent, displaying a planar molecular structure, with two sets of carboxylate, isonitrile, thiophene, and iminodiacetate groups. The blue color originates from a strong absorption peak at 648 nm, accompanied by an unusual fluorescence at 555 nm, with higher energy compared to the main absorption band. RanB forms complexes with lanthanoid ions through the iminodiacetate groups and serves as an effective sensitizer for Tb3+ ions, heightening their emission and improving their use as luminescent agents. Its photo-physical properties and the interaction with Tb3+ have been investigated using absorption spectroscopy, steady-state and time-resolved fluorescence spectroscopy, along with computational methods (ZINDO/S and DFT). The RanB toxicity in human umbilical vein endothelial cells has also been tested, showing a lack of toxicity, holding promising prospects for application as a luminescent and coloring agent in pharmaceuticals and food.

Equilibrium Thermodynamics of Macropa Complexes with Selected Metal Isotopes of Radiopharmaceutical Interest.

To pursue the design of in vivo stable chelating systems for radiometals, a concise and straightforward method toolbox was developed combining NMR, isothermal titration calorimetry (ITC), and europium time-resolved laser-induced fluorescence spectroscopy (Eu-TRLFS). For this purpose, the macropa chelator was chosen, and Lu3+, La3+, Pb2+, Ra2+, and Ba2+ were chosen as radiopharmaceutically relevant metal ions. They differ in charge (2+ and 3+) and coordination properties (main group vs lanthanides). 1H NMR was used to determine four pKa values (±0.15; carboxylate functions, 2.40 and 3.13; amino functions, 6.80 and 7.73). Eu-TRLFS was used to validate the exclusive existence of the 1:1 Mn+/ligand complex in the chosen pH range at tracer level concentrations. ITC measurements were accomplished to determine the resulting stability constants of the desired complexes, with log K values ranging from 18.5 for the Pb-mcp complex to 7.3 for the Lu-mcp complex. Density-functional-theory-calculated structures nicely mirror the complexes' order of stabilities by bonding features. Radiolabeling with macropa using ligand concentrations from 10-3 to 10-6 M was accomplished by pointing out the complex formation and stability (212Pb > 133La > 131Ba ≈ 224Ra > 177Lu) by means of normal-phase thin-layer chromatography analyses.

Revealing the ultrafast spontaneous emission in plasmon-enhanced monolayer semiconductor nano-light sources

Nanoscale spontaneous light sources are promising alternatives to lasers for high-speed optical communications and interconnections through energy-efficient integrated circuits. Yet, developing the spontaneous light sources faster than lasers is hampered by the detection means (e.g., time-resolved fluorescence spectroscopy). Here, by coupling monolayer WSe2 to individual plasmonic nanocavities, we achieved an efficient spontaneous light source with potential ultrafast modulation bandwidth and superior brightness. The ultrafast radiative decay rates can be determined and derived solely from the experimental parameters by combining the coupling strength and the photoluminescence enhancement in a single nanocavity-WSe2 hybrid. As a result, the hybrid light source has a radiative lifetime down to 350 fs, indicating a potential modulation bandwidth up to 440 GHz, which is 10 times of the traditional semiconductor lasers. Furthermore, the quantum yield is enhanced by a factor of over 300-folds up to 20.8% through making full use of the highly confined nanocavity mode. The nanocavity-WSe2 hybrid we built provides a promising approach for constructing high-speed light-emitting devices.

Kinetics of Single-Wall Carbon Nanotube Coating Displacement by Single-Stranded DNA Depends on Nanotube Structure.

Time-resolved fluorescence spectroscopy has been used to study the displacement of adsorbed sodium dodecyl sulfate (SDS) from the surface of single-wall carbon nanotubes (SWCNTs) by short strands of single-stranded DNA. Intensity changes in near-infrared emission peaks of various SWCNT structures were analyzed following the addition of six different (GT)n oligomers (n from 3 to 20) to SDS-coated nanotube samples. There is a strong kinetic dependence on the oligomer length, with (GT)3 giving an initial rate more than 300 times greater than that of (GT)20. For shorter oligos in the (GT)n series, we observe an inverse dependence of the displacement rate on the SWCNT diameter, with SDS displaced from (6,5) more than twice as fast as from (8,7). However, this diameter dependence is reversed for oligos with more than six (GT) units. There is also a systematic dependence of the displacement rate on the nanotube chiral angle that is strongest for (GT)5, leading to a factor of ∼3 initial rate difference between (9,1) and (6,5) despite their identical diameters. To account for these findings, we propose a simple two-step kinetic model in which disruption of the original SDS coating is followed by conformational relaxation of ssDNA on the nanotube surface. The relaxation is relatively fast for ssDNA oligos shorter than 12 bp, making the first step rate-determining. Conversely, relaxation of the longer oligomers is slow enough that the second step becomes rate-determining.

Origin of Energy Dissipation in the Oligomeric Fucoxanthin-Chlorophyll a/c Binding Proteins.

Fucoxanthin-chlorophyll proteins (FCPs) are a family of photosynthetic light-harvesting complex (LHC) proteins found in diatoms. They efficiently capture photons and regulate their functions, ensuring diatom survival in highly fluctuating light. FCPs are present in different oligomeric states in vivo, but functional differences among these FCP oligomers are not yet fully understood. Here we characterized two types of antenna complexes (FCP-B/C dimers and FCP-A tetramers) that coexist in the marine centric diatom Chaetoceros gracilis using both time-resolved fluorescence and transient absorption spectroscopy. We found that the FCP-B/C complex did not show fluorescence quenching, whereas FCP-A was severely quenched, via an ultrafast excitation energy transfer (EET) pathway from Chl a Qy to the fucoxanthin S1/ICT state. These results highlight the functional differences between FCP dimers and tetramers and indicate that the EET pathway from Chl a to carotenoids is an energy dissipation mechanism conserved in a variety of photosynthetic organisms.

Photophysical properties of several multi-branched oligomers: An ultrafast excited state dynamics and quantum chemical calculation study

Multi-branched oligomers F1, F2 and F3 were investigated by spectroscopic experiments as well as quantum chemical calculations to elucidate the structure–property relationships and intramolecular charge transfer (ICT) characteristics of typical nonlinear optical materials. A better ICT property of F2 is obtained by replacing terminal electron donors with stronger electron-donating ability. The degree of ICT is effectively increased, which can be clearly seen from the frontier molecular orbitals contribution of central anthracene between HOMO and LUMO. The central group plays a major role in the direction as well as effective path of ICT process. In the X-shaped oligomers with anthracene as central group, ICT process takes place from terminal groups of [Formula: see text] position branches, to the central anthracene group. However, the electron distribution as well as the ICT of tri-branched oligomer F3 with triazine as central group is not symmetric. ICT process of F3 takes place from terminal triphenylamine groups to the central triazine and two fluorene groups at [Formula: see text] position branches. Y-shaped oligomer F3 has a longer lifetime of ICT state as well as a higher fluorescence quantum yield, which is consistent with the results of time-resolved fluorescence spectroscopy. Z-scan results show that the TPA cross-section value of F3 is 10.6 and 2.9 times higher than that of X-shaped F1 and F2. The dynamics curves of transient absorption spectroscopy also indicate that oligomer F3 structure has relatively stronger ICT properties. To verify the substituent effect, two linear molecules F4 and F5 were also calculated. The quantum chemical calculations result shows that the branches at positions 4 and 11 of the central anthracene group have little effect on the electron cloud distribution, and there are indeed significant differences in the contributions of branches at different positions. Our results may provide some reference for molecular design.

Tetracene Dimers: A Platform for Balancing Intramolecular Up- and Down-Conversion

Photon energy conversion can be accomplished in two opposing manners, down conversion (i.e., singlet fission, SF), and up-conversion (often referred to as triplet-triplet annihilation up-conversion, TTA-UC), both of which have the potential to help overcome the Shockley-Queisser limit of single-junction solar cells. Inter-chromophore electronic coupling plays opposing roles in these two processes. The energies of the lowest singlet excited state and twice the triplet excited state are comparable in tetracene dimers, which exhibit both up- and down-conversion. Here, we have designed meta-phenylene- and 1,3-diethynyladamantyl-linked tetracene dimers with different electronic coupling to probe the interplay between intramolecular SF (intra-SF) and intramolecular TTA-UC (intra-TTA-UC) viasteady-state and time-resolved absorption and fluorescence spectroscopy. In addition, temperature-dependent measurements are carried out to shed light on the thermal effects on intra-SF and intra-TTA-UC. We have also used a Pd-phthalocyanine as photosensitizer to enable intra-TTA-UC in the two dimers via indirect photo-excitation in the near-infrared. These results not only reveal the interplay between intra-SF and intra-TTA-UC, but also provide guidelines and strategies for the design of photon down- and up-converting materials.

Highly sensitive and selective fluorescence and smartphone-based sensor for detection of L-dopa using nitrogen sulphur graphene quantum dots

The level of L-dopa in the body has a significant impact on treatment of Parkison’s disease. L-Dopa, a precursor to the neurotransmitter dopamine has been unanimously recommended as the gold standard for treating the condition. The present work focuses on creating a flexible platform for the quantitative and targeted detection of L-dopa using nitrogen sulphur co-dopped graphene quantum dots (NSGQD). The NSGQD were prepared by using thiourea and citric acid via calcination process. The synthesised NSGQD emitted bright bluish green light with the addition of L-Dopa to NSGQD in basic condition the fluorescence of NSGQD was quenched. L-dopa is transformed into dopaquinone in an alkaline environment and photoinduced electron transfer causes fluorescence quenching. As a result, the intensity of the NSGQD fluorescence gradually decreased as the L-dopa concentration rose in wide concentration range and low limit of detection (LOD) was established to be 7.8 nM relative to other analytes, quinone derivatives and amino acids the NSGQD showed greater specificity to L-dopa. The sensing mechanism was thoroughly investigated using steady state, time-resolved fluorescence spectroscopy, UV–Vis absorption measurements and fluorescent studies. Additionally, this also proves through smartphones portable device using color detector software. Our research paves the way for the creation of an affordable biosensor that will work well for finding L-dopa in actual samples. Computational studies were carried out using density functional theory for better understanding the interactions of dopa with NSGQD indicating hydrogen bonds are formed between carbonyl group of dopaquinone with functional groups of NSGQD.

Exciplex Emission and Förster Resonance Energy Transfer in Polycyclic Aromatic Hydrocarbon-Based Bischromophoric Cyclophanes and Homo[2]catenanes.

Energy transfer and exciplex emission are not only crucial photophysical processes in many living organisms but also important for the development of smart photonic materials. We report, herein, the rationally designed synthesis and characterization of two highly charged bischromophoric homo[2]catenanes and one cyclophane incorporating a combination of polycyclic aromatic hydrocarbons, i.e., anthracene, pyrene, and perylene, which are intrinsically capable of supporting energy transfer and exciplex formation. The possible coconformations of the homo[2]catenanes, on account of their dynamic behavior, have been probed by Density Functional Theory calculations. The unique photophysical properties of these exotic molecules have been explored by steady-state and time-resolved absorption and fluorescence spectroscopies. The tetracationic pyrene-perylene cyclophane system exhibits emission emanating from a highly efficient Förster resonance energy transfer (FRET) mechanism which occurs in 48 ps, while the octacationic homo[2]catenane displays a weak exciplex photoluminescence following extremely fast (<0.3 ps) exciplex formation. The in-depth fundamental understanding of these photophysical processes involved in the fluorescence of bischromophoric cyclophanes and homo[2]catenanes paves the way for their use in future bioapplications and photonic devices.

Bovine serum albumin protected Cd8 nanoclusters as efficient two-photon absorbers for near-infrared excited fluorescence imaging of intracellular pH

Metal nanocluster-based fluorescent sensors have made great progress in the field of analytical chemistry, but their practical applications in biological sensing were limited by poor stability, short wavelength excitation and low quantum yield. It is of great significance to develop NIR-excited metal nanocluster-based fluorescence sensors with high quantum yield. In contrast to noble metal nanoclusters (e.g., Au, Ag, and Pt), stable and affordable fluorescent metal nanoclusters have received relatively less research attention, with the exception for Cu nanoclusters. Herein, we developed a rapid one-pot route to synthesize cadmium nanoclusters employing bovine serum albumin (BSA) as both reducing and templating agent. The obtained Cd8NCs exhibited bright fluorescence emission with quantum yield of 13.8%. Of particular interest, the Cd8NCs showed remarkable capability as two-photon absorbers, with a two-photon absorption (TPA) cross section up to 1588 GM (excited at 730 nm). The TPA cross section was higher than that of BSA-protected AuNCs, and even exceeded that of conventional dyes by two orders of magnitude. In addition, the Cd8NCs exhibited pH-sensitive photoluminescence, and the pH-responsive mechanism was revealed by time-resolved fluorescence spectroscopy, transient absorption spectroscopy, etc. Benefiting from protein coating, Cd8NCs showed excellent biocompatibility and were successfully utilized as two-photon excited fluorescence sensors for intracellular pH.

Molecular aggregation kinetics of Heteropolyene: An Experimental, topological and solvation dynamics studies

Herein, we have demonstrated the solvent specific ground state and excited state aggregates of the molecule ((1E,2E)-1,2-bis((E)-3-phenylallylidene)hydrazine: BISCH) in solution. The nature of aggregation at ground state and excited state is different in H2O solvent. The rate of aggregation in water is calculated from steady state absorption and fluorescence spectroscopy respectively. Excited state fluorescence behaviour contributed from aggregates and non-aggregates species have been identified by time resolved fluorescence spectroscopy in H2O. Aggregation is highly sensitive towards solvent polarity and nature of solvent. The effect of solvent on aggregation process has been discussed and explained on the basis of relative change of hydrophobic and hydrophilic interaction of solute-solvents in solution. Further, J-type aggregation of BISCH is also observed in H2O. Further, using 1st order aggregation kinetic model for ground and excited state,) aggregation rate constant has been calculated and found to 8.0x10-4s−1 ((kagg@312 nm) and 1.2x10-4s−1 (kagg@413 nm) respectively. Effect on molecular geometry depending upon Interaction sites of BISCH and solvent molecule is also discussed with the results from DFT calculation. NBO, NCI, DOS, MESP along with various topological analysis are performed for BISCH in water. For BISCH…water molecular system, NBO interaction is observed due to delocalization of lone pair of O35 and N36 to antibonding of H37-O38 and H40-O41, respectively. ELF, LOL, AIM and ALIE calculation are employed to locate the site and magnitude of hydrogen bonding interactions. The AIMD study for BISCH in water shows minimum of the total energy between 125 and 175 fs and 225–275 fs. N…H-O hydrogen bonding interactions such as N36-H40 and N35-H37 varies from 1.8 to 2.6 Å during the molecular dynamics simulation.

Application of steady-state and time-resolved fluorescence spectroscopy in identification of cold-pressed vegetal oils

Monitoring the quality of food products is very important, due to the fact that substances potentially harmful to consumers may be formed during production and storage. In addition, vegetal oils are subject to falsification, which is based mainly on mixing and adding other, usually cheaper equivalents or providing false data on the composition and origin. In this way, the path from a very healthy product to a product that has a negative impact on the human body is very short. In this study fluorescence spectra and fluorescence decay kinetics of selected cold-pressed oils were characterized and the origin of the observed fluorescence bands was discussed. The obtained fluorescence characteristics were found to be the unique fingerprints of the individual oils and showed evident differences which arise from specific qualitative and quantitative compositions of the oils. The most apparent differences in the shape of fluorescence bands were observed in the emission spectrum at excitation wavelength 350 nm and in the excitation spectrum recorded at emission wavelength 500 nm. The obtained results show the utility of the applied steady-state and time –resolved fluorescence measurements in the identification of the tested vegetal oils.

Tetracene Dimers: A Platform for Intramolecular Down- and Up-conversion.

Photon energy conversion can be accomplished in many different ways, including the two opposing manners, down-conversion (i.e., singlet fission, SF) and up-conversion (i.e., triplet-triplet annihilation up-conversion, TTA-UC). Both processes have the potential to help overcome the detailed balance limit of single-junction solar cells. Tetracene, in which the energies of the lowest singlet excited state and twice the triplet excited state are comparable, exhibits both down- and up-conversion. Here, we have designed meta-diethynylphenylene- and 1,3-diethynyladamantyl-linked tetracene dimers, which feature different electronic coupling, to characterize the interplay between intramolecular SF (intra-SF) and intramolecular TTA-UC (intra-TTA-UC) via steady-state and time-resolved absorption and fluorescence spectroscopy. Furthermore, we have used Pd-phthalocyanine as a sensitizer to enable intra-TTA-UC in the two dimers via indirect photoexcitation in the near-infrared part of the solar spectrum. The work is rounded off by temperature-dependent measurements, which outline key aspects of how thermal effects impact intra-SF and intra-TTA-UC in different dimers.

Simultaneous Spectral Temporal Modelling for a Time-Resolved Fluorescence Emission Spectrum

Innovations in complementary metal-oxide semiconductor (CMOS) single-photon avalanche diode (SPAD) technology has featured in the development of next-generation instruments for point-based time-resolved fluorescence spectroscopy (TRFS). These instruments provide hundreds of spectral channels, allowing the collection of fluorescence intensity and fluorescence lifetime information over a broad spectral range at a high spectral and temporal resolution. We present Multichannel Fluorescence Lifetime Estimation, MuFLE, an efficient computational approach to exploit the unique multi-channel spectroscopy data with an emphasis on simultaneous estimation of the emission spectra, and the respective spectral fluorescence lifetimes. In addition, we show that this approach can estimate the individual spectral characteristics of fluorophores from a mixed sample.

One-Pot Synthesis and Excited-State Dynamics of Null Exciton-Coupled Diketopyrrolopyrroles Oligo-Grids.

Exciton coupling in molecular aggregates plays a vital role in impacting and fine-tuning optoelectronic materials and their efficiencies in devices. A versatile platform to decipher aggregation-property relationships is built around multichromophoric architectures. Here, a series of cyclic diketopyrrolopyrrole (DPP) oligomers featuring nanoscale gridarene structures and rigid bifluorenyl spacers are designed and synthesized via one-pot Friedel-Crafts reaction. DPP dimer [2]Grid and trimer [3]Grid, which are cyclic rigid nanoarchitectures of rather different sizes, are further characterized via steady-state and time-resolved absorption and fluorescence spectroscopies. They exhibit monomer-like spectroscopic signatures in the steady-state measurements, from which null exciton couplings are derived. Moreover, in an apolar solvent, high fluorescence quantum yields and excited-state dynamics that resembled DPP monomer are gathered. In a polar solvent, the localized singlet excited state on a single DPP dissociates into the adjacent null coupling DPP with charge transfer characteristics. This pathway facilitates the evolution ofthe symmetry-broken charge-separated state (SB-CS). Notable is the fact that the SB-CS of [2]Grid is, on one hand, in equilibrium with the singlet excited state and promotes, on the other hand, the formation of the triplet excited state with a yield of 32% via charge recombination.