Time-resolved Measurements Research Articles

Vitamin B2 Operates by Dual Thermodynamic and Kinetic Mechanisms to Selectively Tailor Urate Crystallization.

Here we demonstrate how a biologically relevant molecule, riboflavin (vitamin B2), operates by a dual mode of action to effectively control crystallization of ammonium urate (NH4HU), which is associated with cetacean kidney stones. In situ microfluidics and atomic force microscopy experiments confirm a strong interaction between riboflavin and NH4HU crystal surfaces that substantially inhibits layer nucleation and spreading by kinetic mechanisms of step pinning and kink blocking. Riboflavin does not alter the distribution of tautomeric urate isomers, but its adsorption on NH4HU crystal surfaces does interfere with the effects of minor urate tautomer by limiting its ability to induce NH4HU crystal defects while also suppressing NH4HU nucleation and inhibiting crystal growth by 80% at an uncharacteristically low modifier concentration. Time-resolved spectroscopy measurements, ab initio calculations, and molecular dynamics simulations confirm that each riboflavin molecule forms a complex with six or more urate molecules to lower supersaturation, thereby reducing the rate of NH4HU crystallization by a thermodynamically driven mechanism. The degree of complexation observed for riboflavin far exceeds that of common chelating agents, and results in crystal dissolution when the free urate concentration falls below NH4HU solubility. The synergism that is created by riboflavin's dual kinetic and thermodynamic mechanisms is rarely achieved by more conventional crystal growth inhibitors. These insights offer new approaches that could be influential for the design of molecular modifiers in crystal engineering applications, the development of therapeutics for pathological conditions, and establishing broader understanding of the roles played by foreign agents in natural and biological crystallization.

Reaction and interaction dynamics of azobenzene-tethered DNA with T7 RNA polymerase.

Reaction and interaction dynamics of azobenzene-tethered DNA (photoresponsive DNA) with T7 RNA polymerase (T7RNAP) were studied after photoisomerization of azobenzene from the cis- to trans-forms using the transient grating (TG) and time-resolved fluorescence polarization techniques. Two types of photoresponsive DNA were examined: AzoPBD, tethered at the protein binding site, and AzoTATA, tethered at the unwinding site. A diffusion change was observed after photoexcitation of cis-AzoPBD within 1 ms, and this change is explained in terms of a structural change from a bent to an extended conformation upon the cis-to-trans photoisomerization. The association and dissociation rates of cis- and trans-AzoPBD-T7RNAP complex were measured by the fluorescence polarization measurements, and the dissociation constants for cis- and trans-AzoPBD were respectively determined to be 3.9 μM and 21 μM. The result indicates that trans-AzoPBD is dissociated upon photoexcitation of cis-AzoPBD-T7RNAP complex. The efficient dissociation is mainly caused by a small association rate constant. The time-resolved diffusion measurement showed a conformational change with a time constant of 2.4 ms and a dissociation reaction with a slower rate, which depends on the concentration of T7RNAP. Although AzoTATA does not exhibit significant structural changes upon isomerization, a diffusion change was observed upon photoexcitation of AzoTATA-T7RNAP. The origin is attributed to changes from the unwound to closed states of AzoTATA, but AzoTATA does not dissociate from T7RNAP. These findings highlight a critical role of the azobenzene insertion position in modulating DNA-T7RNAP interaction dynamics, providing new insights into light-regulated transcription control.

Simulation of a pulsed CO2 plasma based on a six-temperature energy approach

Abstract Recent time-resolved measurements of gas and vibrational temperatures in pulsed glow discharges have fostered the development and validation of detailed kinetic models to understand the underlying heating dynamics. The models published so far have been successful in identifying the fundamental processes underlying vibrational and gas heating in pure CO2 discharges; however, this has come at the cost of including vibrational kinetics with thousands of reactions. This makes these models not compatible with self-consistent computational fluid dynamics (CFD) codes, which are needed to develop new plasma reactors operating at high pressures or with complex flow patterns and capture the relevant dynamics in multi-dimension. In this work, we solve separate energy balance equations for the asymmetric and symmetric vibrational modes of CO2, as well as for the vibrational modes of CO and O2, the gas temperature, and the electron temperature, making it a six-temperature (6T) plasma model. This eliminates the need to include a vast array of vibrational levels as separate species, drastically reducing the number of reactions in the model. The model is compared with experimental measurements conducted in a pulsed CO2 glow discharge at 6.7 mbar. Excellent agreement is observed for the temporal evolution of the vibrational and gas temperatures, confirming that our approach is suitable for modeling systems under significant non-equilibrium conditions, paving the way for coupling detailed CO2/CO/O2/O kinetics with CFD codes.

Synthesis of zwitterionic asymmetric and symmetric carboxy-imidazolium derivatives and their use in molecular interactions with bovine serum albumin.

For the first time asymmetric and symmetric carboxytriazoleimidazolium derivatives with different structures were synthesized. The critical micellization concentration (CMC) value was estimated using a pyrene fluorescent probe and the solubility of Orange OT. The complexation ability of carboxytriazoleimidazolium derivatives toward bovine serum albumin (BSA) has been investigated by various physico-chemical methods: fluorescence spectroscopy, electrophoretic light scattering and circular dichroism. The effect of the oxo-bridge and the presence of a hydrophobic fragment in the structure of the molecules and its influence on their aggregation properties and interaction with BSA has also been studied. According to the fluorescence data, only in the case of the asymmetric derivatives with long alkyl fragments a shift of the BSA emission maximum is observed, indicating a change in the BSA microenvironment. The secondary structure of BSA remains virtually unchanged in the presence of carboxytriazoleimidazolium derivatives, as shown by circular dichroism. No significant changes in the structure of BSA were observed in the presence of zwitterionic compounds with an oxo-bridge at concentrations where fluorescence quenching occurs, as shown by time-resolved fluorescence measurements. Electrophoretic light scattering showed a recharging of BSA from a negative to a positive zeta potential in the presence of amphiphilic derivatives.

The role of TCNQ for surface and interface passivation in inverted perovskite solar cells

The noticeable growth in the power conversion efficiency of solution-processed organo-inorganic halide perovskite solar cells (OIHPSCs) incited the photovoltaic community to look for limitations that hurdle the commercialization process. The surface and interface defects between the perovskite and electron transport layers are among the main challenges that cause significant non-radiative recombination losses, thereby they result in poor performance and stability. In this work, tetracyanoquinodimethane (TCNQ), a strong electron acceptor molecule, is applied at the interface between the photoactive perovskite and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) layers to modify the interface, and enhance device performance and stability. Steady-state and time-resolved photoluminescence measurements were used to characterize the role of the TCNQ passivation in reducing non-radiative recombination of charge carriers. Current density versus voltage (J-V) measurements show improvement in devices open-circuit voltage (Voc), short-circuit current density (Jsc), and fill factor (FF) for devices with TCNQ interface passivation, which is attributed to suppressed non-radiative recombination. In addition, a noticeable improvement in the device’s stability was observed. This study reveals the dual role of TCNQ passivation in improving the photoelectric properties and stability of ambient air processed perovskite devices with the pin architecture.

Spatiotemporal Spectroscopy of Fast Excited-State Diffusion in 2D Covalent Organic Framework Thin Films.

Covalent organic frameworks (COFs), crystalline and porous conjugated structures, are of great interest for sustainable energy applications. Organic building blocks in COFs with suitable electronic properties can feature strong optical absorption, whereas the extended crystalline network can establish a band structure enabling long-range coherent transport. This peculiar combination of both molecular and solid-state materials properties makes COFs an interesting platform to study and ultimately utilize photoexcited charge carrier diffusion. Herein, we investigated the charge carrier diffusion in a two-dimensional COF thin film generated through condensation of the building blocks benzodithiophene-dialdehyde (BDT) and N,N,N',N'-tetra(4-aminophenyl)benzene-1,4-diamine (W). We visualized the spatiotemporal evolution of photogenerated excited states in the 2D WBDT COF thin film using remote-detected time-resolved PL measurements (RDTR PL). Combined with optical pump terahertz probe (OPTP) studies, we identified two diffusive species dominating the process at different time scales. Initially, short-lived free charge carriers diffuse almost temperature-independently before relaxing into bound states at a rate of 0.7 ps-1. Supported by theoretical simulations, these long-lived bound states were identified as excitons. We directly accessed the lateral exciton diffusion within the oriented and crystalline film, revealing remarkably high diffusion coefficients of up to 4 cm2 s-1 (200 K) and diffusion lengths of several hundreds of nanometers and across grain boundaries. Temperature-dependent exciton transport analysis showed contributions from both incoherent hopping and coherent band-like transport. In the transport model developed based on these findings, we discuss the complex impact of order and disorder on charge carrier diffusion within the WBDT COF thin film.

Nonlinear photoexcitation processes at a MAPbBr3/GaAs heterointerface

Abstract While a significant part of the solar energy lies in the infrared range, common semiconductors cannot absorb this part of the solar irradiance by direct band-to-band transitions, because the corresponding photon energies are below the bandgap energy. Two-step photon up-conversion (TPU) is one of the processes that allows us to harvest energy in the region below the bandgap, and one possible approach to realize a TPU-based solar cell is to use an AlGaAs/GaAs heterointerface with quantum dots in order to induce additional intraband transitions. On the other hand, here we report on the TPU phenomenon at a methylammonium lead bromide/gallium arsenide (MAPbBr3/GaAs) heterointerface without quantum dots. For this heterojunction, we observed high-energy photoemission by low-energy photoinjection, demonstrating the TPU. By using photoluminescence (PL) and time-resolved PL measurement techniques, we elucidate the mechanism of the PL emission from MAPbBr3 observed from MAPbBr3/GaAs samples. Through the comparisons of the experimental PL and TRPL results between the MAPbBr3/GaAs and MAPbBr3/Glass-substrate samples, we successfully distinguish the TPU phenomenon from the ordinal two-photon absorption of MAPbBr3. Our findings in the TPU at the MAPbBr3/GaAs heterointerface may help to realize quantum-dot-free photon up-conversion solar cells.

Detection of ultrafast electron energization by whistler-mode chorus waves in the magnetosphere of Earth

Electromagnetic whistler-mode chorus waves are a key driver of variations in energetic electron fluxes in the Earth’s magnetosphere through the wave-particle interaction. Traditionally understood as a diffusive process, these interactions account for long-term electron flux variations (> several minutes). However, theories suggest that chorus waves can also cause rapid (< 1 s) electron acceleration and significant flux variations within less than a second through a nonlinear wave-particle interaction. Detecting these rapid accelerations has been a great challenge due to a limited time resolution of conventional particle instruments. Here, we employ an analysis technique to enhance the time resolution of the particle measurements, revealing rapid electron flux variations within less than one second associated with chorus waves. This technique exposes short-lived flux increases significantly larger than those observable with the standard time resolution. Our findings indicate that these transient flux variations result from the nonlinear acceleration of electrons induced by the chorus waves, highlighting the importance of nonlinear wave-particle interactions in creating high energy electrons in the Earth’s magnetosphere. The same acceleration mechanism should operate in the magnetospheres of Jupiter and Saturn where chorus waves are present, and in laboratory plasma environments when chorus-like waves are excited.

Adaptable Blueprint for Non-metal Near-Infrared Organic Photocatalysts by Aromatic Sulfones.

We present a versatile approach to designing and utilizing high-performance nonmetal near-infrared (NIR) organic photocatalysts based on aromatic sulfones. Current NIR photocatalysts are mainly metal complexes and inorganic materials, while the few reported nonmetal organic NIR photocatalysts primarily use photosensitization to produce active species such as singlet oxygen. Our sulfone-rosamine-based redox photocatalyst 3 demonstrates exceptional capabilities, including high ability for metal-free photo-oxidative bromination, intrinsically oxygen-independent redox reactions, and remarkable photostability with a turnover number (TON) exceeding 2800. We showcase the photocatalyst's efficacy in photo-oxidative bromination of aromatic compounds under 738 nm illumination. The reaction mechanism is elucidated through electrochemical studies, time-resolved spectral measurements, and DFT calculations. Transient absorption measurements using the randomly interleaved pulse train (RIPT) method reveal the photoexcited state of 3 in the reaction. The photocatalyst 3 demonstrated its versatility for several aromatic substances, including those exhibiting strong light absorption in the visible region. This aromatic sulfone-based approach offers a robust blueprint for developing nonmetal NIR organic photocatalysts with superior photo-oxidation ability and stability, addressing key limitations of conventional organic NIR photocatalysts.

Two-Dimensional Phototransistors with van der Waals Superstructure Contacts for High-Performance Photosensing.

Semiconducting transition metal dichalcogenides (TMDs) possess exceptional photoelectronic properties, rendering them excellent channel materials for phototransistors and holding great promise for future optoelectronics. However, the attainment of high-performance photodetection has been impeded by challenges pertaining to electrical contact. To surmount this obstacle, we introduce a phototransistor architecture, in which the WS2 channel is connected with an alternating WS2-WSe2 strip superstructure, strategically positioned alongside the source and drain contact regions. Illumination triggers efficient separation of photoexcited electrons and holes due to the type-II staggered band alignment within the superstructure. Consequently, the contact regions exhibit degenerately doped n+ WS2 and p+ WSe2 strips under light illumination, resulting in minimal contact resistivity with the metal electrodes. The resultant WS2 phototransistor exhibits a remarkable responsivity of 2.4 × 106 mA/W and an impressive detectivity of 2.6 × 1012 Jones. Furthermore, our time-resolved measurements reveal the absence of persistent photoconductance. This proposed phototransistor architecture provides a route for high-performance photodetection, effectively surpassing previous limitations associated with electrical contact.

Bayesian method in optical emission spectroscopy: temporal evolution of electron density from time-integrated Hα emission and validation with time-resolved measurements for pulsed nanosecond discharges in water

Bayesian method in optical emission spectroscopy: temporal evolution of electron density from time-integrated H_α emission and validation with time-resolved measurements for pulsed nanosecond discharges in water

The Influence of Length and Sequence of Complementary Oligonucleotides on the Spectral and Time-Resolved Fluorescence Properties of an H-Type Excitonic Dimer-Bearing Antisense Oligonucleotide.

We have previously found that the presence of an H-type excitonic dimer formed by two fluorophores covalently bound to an oligonucleotide allows the delivery of such a polymer into live cells without inducing toxicity. We are now using time-resolved fluorescence measurements in solution to understand the molecular dynamics of an antisense probe and how pairing with complementary sense strands of various lengths and degrees of complementarity affects the antisense strand's properties. We report that a DNA strand composed of 30 residues and labeled with an H-type excitonic Cyanine-5/Cyanine-5 dimer shows a predominant 1.9 ns lifetime decay term accompanied by a shorter (0.5 ns) secondary lifetime. Similar values were measured for this excitonic dimer-bearing antisense strand following binding with a series of sense strands of varying lengths and compositions. However, significant differences in both time-resolved and steady-state anisotropy values were found, depending on the level of duplex formation through hydrogen bonding between sense and antisense sequences. More specifically, the anisotropy measurements of the double-labeled single-chain probe showed increases as the two intramolecular fluorophores were induced to separate with values dependent on the length and sequence of complementary sense strands. These differences suggest induced changes in the degrees of wobbling, tumbling, and spinning.

Time-resolved fluorescence measurements of dissolved organic matter (DOM) as a function of environmental parameters in estuarine waters.

Fluorescent lifetimes of dissolved organic matter (DOM) and associated physicochemical parameters were measured over 14months in an estuary in Southern California, USA. Measurements were made on 77 samples from sites near the inlet, mid-estuary, and outlet to maximize the range of physicochemical variables. Time-resolved fluorescence data were well fit to a triexponential model with an intermediate lifetime component (τ1: 1 to 5ns), a long lifetime component (τ2: 2 to 15ns), and a short lifetime component (τ3: < 1ns). The amplitude of the short-lived component dominated all measurements (60-70%). However, fractional contributions to steady-state fluorescence were dominated by the intermediate and long-lived components at most wavelengths. Lifetimes varied as a function of both excitation and emission wavelength suggesting structural differences in DOM fluorophores. Lifetimes decreased from the estuary inlet to the outlet and were positively correlated with absorbance and DOC concentrations and negatively correlated with salinity and spectral slope. Quenching experiments with halide ions demonstrated that fluorophores are quenched by heavy ions and that different fluorophores are quenched at different rates. However, concentrations of ions in seawater are not high enough for quenching to completely account for observed lifetime changes across the estuary. The observed variation in lifetimes between sites is instead primarily attributed to structural changes associated with DOM processing. Higher lifetimes are associated with less processed material at the inlet site.

The impact of encapsulation in cyclodextrin nanocavities on the participation of hydrogen bond assisted intramolecular charge transfer in fluorescence emission

This study investigates how incorporation of D-π-A derivatives in various cyclodextrin structures affects the identification of excited-state emission characteristics, focusing on the contribution of intramolecular charge transfer and hydrogen bond-assisted intramolecular charge transfer emissive states. In this context, the photophysical properties of 4-(5-(4-methoxyphenyl)thiophen-2-yl)benzamidine (I) and 2-fluoro-4-(5-(4-methoxyphenyl)thiophen-2-yl)benzamidine (II) in neutral aqueous solution and upon inclusion in various cyclodextrin derivatives were investigated by steady state and time-resolved measurements. Despite the very limited changes in the absorption spectra of the guest molecules upon addition of CDs, significantly large changes were observed in their steady-state fluorescence spectroscopy, both in the quantum yield of the fluorescence emission and their fluorescence lifetime results. Fluorescence decay profiles of (I) and (II) exhibited good fits with biexponential decay functions both in the presence and absence of the investigated CDs, with their respective contributions significantly dependent on the concentration of added cyclodextrin. The association constants derived from fluorescence decay measurements closely matched those obtained from steady-state fluorescence measurements. Inclusion of I and II in α-CD, β-CD, Mβ-CD, or HPβ-CD was confirmed using 1H NMR measurements, with notable 2D NOESY effects observed specifically for II..HPβ-CD complexes.

Time-resolved cross-beam energy transfer in strongly damped regime on the Laser Mégajoule facility

We report on an experiment performed at the Laser Mégajoule facility to investigate on cross-beam energy transfer (CBET) between two kilojoule-nanosecond laser beams propagating through a neo-pentane gas pipe. CBET is diagnosed using time-resolved transmission measurements and x-ray imagers. The time-resolved laser transmission is obtained using laser calibrated x-ray emission conversion on a gold foil located behind the target. Different shots, with and without frequency shift, allow to control the amount of power transferred between the two beams. In particular, we observe that the blue-shifted pulse is significantly depleted during several nanoseconds when using a frequency shift between the laser beams. The time-resolved data provide quantitative comparisons for benchmarking CBET modeling in our radiative hydrodynamic code. It appears that the x-ray emission from the gold foil is recovered only when no saturation of the ion acoustic wave amplitude is applied in our linear kinetic modeling. Yet, the measured signal is not sufficiently accurate to discriminate between CBET models assuming a perfect plane wave closure and those taking into account the speckle structure of the field with smoothing by spectral dispersion.

Micro- and milli-fluidic sample environments for in situ X-ray analysis in the chemical and materials sciences.

X-ray-based methods are powerful tools for structural and chemical studies of materials and processes, particularly for performing time-resolved measurements. In this critical review, we highlight progress in the development of X-ray compatible microfluidic and millifluidic platforms that enable high temporal and spatial resolution X-ray analysis across the chemical and materials sciences. With a focus on liquid samples and suspensions, we first present the origins of microfluidic sample environments for X-ray analysis by discussing some alternative liquid sample holder and manipulator technologies. The bulk of the review is then dedicated to micro- and milli-fluidic devices designed for use in the three main areas of X-ray analysis: (1) scattering/diffraction, (2) spectroscopy, and (3) imaging. While most research to date has been performed at synchrotron radiation facilities, the recent progress made using commercial and laboratory-based X-ray instruments is then reviewed here for the first time. This final section presents the exciting possibility of performing in situ and operando X-ray analysis in the 'home' laboratory and transforming microfluidic and millifluidic X-ray analysis into a routine method in physical chemistry and materials research.

Oxidant concentrations and photochemistry in a vehicle cabin.

Indoor air quality (IAQ) in vehicles can be important to people's health, especially for those whose occupations require them to spend extensive time in vehicles. To date, research on vehicle IAQ has primarily focused on direct emissions as opposed to chemistry happening in vehicle cabins. In this work, we conducted time-resolved measurements of the oxidants and oxidant precursors ozone (O3), nitric oxide (NO), nitrogen dioxide (NO2), and nitrous acid (HONO) inside the cabin of a 2012 Toyota Rav4 under varying ventilation conditions (i.e., car off, car on with passive ventilation, car on with mechanical ventilation via the recirculating fan, and car on with mechanical ventilation via the direct fan). Ozone levels inside the vehicle were significantly lower than outdoors under most conditions, and were approximately half the outdoor levels when the direct fan was in operation. Nitric oxide and NO2 concentrations were very low both inside the vehicle and outdoors. Nitrous acid levels in the vehicle were lower than reported values in other indoor environments, though much higher than expected outdoor levels. We also investigated the potential for photochemical production of radicals in the vehicle. Time- and wavelength-resolved solar irradiance spectra were collected, and steady state hydroxyl radical (OH) and nitrate radical (NO3) concentrations were calculated. Steady state OH concentrations were predicted to be similar to those in air masses in residences illuminated by sunlight, suggesting the importance of HONO photolysis in vehicles. Conversely, nitrate radicals (NO3) were not considered significant indoor oxidants in our study due to rapid titration by NO. Overall, our findings emphasize the importance of both air exchange and photochemistry in shaping the composition of air inside vehicles.

Measurements and kinetic modeling of O2 vibrational kinetics in O2–Ar mixtures partially dissociated by a Ns pulse discharge

Abstract Vibrational kinetics of O2 is studied during the O atom recombination in an O2-Ar mixture, partially dissociated by a burst of ns discharge pulses in a heated plasma flow reactor. The time-resolved temperature in the discharge afterglow is determined by Rayleigh scattering. Time-resolved O atom number density is measured by ps Two-Photon absorption Laser Induced Fluorescence (TALIF), calibrated in xenon. Time-resolved vibrational level populations of molecular oxygen, O2(v=8-20), are measured by ps Laser Induced Fluorescence (LIF), with the absolute calibration by NO LIF. Time-resolved ozone number density is monitored by broadband UV absorption. The results are compared with the predictions of a state-specific kinetic model. The experimental data indicate a rapid initial decay of O2(v) populations generated by electron impact in the discharge, due to the vibration-translation (V-T) relaxation by O atoms. This is followed by a slower population reduction, on the time scale much longer compared to that for V-T relaxation or vibration-vibration (V-V) exchange. Both O atoms and the O2(v) populations decay on the same time scale, indicating that chemical reactions initiated by the O atom recombination result in the generation of vibrationally excited O2 molecules. These trends are reproduced by the kinetic model, which shows that the reaction of O atoms with ozone is the dominant pathway of O2(v) generation at the present conditions. The predicted relative O2(v) populations are close to the experimental results, but absolute number densities differ from the experimental data. This is likely due to uncertainties in the absolute calibration of LIF measurements and in the spectroscopic model used in the data reduction. The present work demonstrates the capability for the absolute, time-resolved measurements of vibrationally excited O2 in recombining gas flows, to quantify the energy partition in the recombination reactions.

Optoelectronic Properties and Fluorescence Lifetime Imaging Application of Donor-Acceptor Dyads Derived From 2,6-DicarboxyBODIPY.

Donor-acceptor BODIPY dyads, functionalized at the 2 and 6 positions with benzyl ester (BDP-DE) or carboxylic acid (BDP-DA) groups, were synthesized and characterized for their optoelectronic properties. The introduction of carbonyl groups increased the reduction potential of the BODIPY core by 0.15-0.4 eV compared to alkyl-substituted analogs. These dyads exhibited efficient intramolecular charge separation and triplet state formation through spin-orbit charge transfer intersystem crossing (SOCT-ISC), achieving singlet oxygen quantum yields of up to 92%, modulated by solvent polarity. The fluorescence and singlet oxygen generation of BDP-DAs depended on the ionization state of the carboxylic groups. Complexation of BDP-DAs with bovine serum albumin (BSA) significantly extended their excited state lifetimes, as shown by time-resolved fluorescence measurements. Fluorescence lifetime imaging microscopy (FLIM) studies in human colorectal carcinoma (HCT116) cells and pig small intestinal organoids (enteroids) revealed subcellular localization patterns. Specifically, the diacid with a dimethoxyphenyl group (DA1) displayed longer lifetimes in lipid-droplet-like structures, while the diacid containing a meso-anthracenyl group (DA2) formed distinct 'islands' in cell monolayers, exhibiting a lifetime gradient. These results underscore the potential of donor-acceptor BODIPYs as fluorescent probes for distinguishing cellular environments.

Dual-fluorescent starch biopolymer films containing 5-(4-nitrophenyl)-1,3,4-thiadiazol-2-amine powder as a functional nanofiller

Physical and photophysical properties of starch-based biopolymer films containing 5-(4-nitrophenyl)-1,3,4-thiadiazol-2-amine (NTA) powder as a nanofiller were examined using atomic force microscopy (AFM), Fourier-transform infrared spectroscopy (FTIR), stationary UV-Vis and fluorescence spectroscopy as well as resonance light scattering (RLS) and time-resolved measurements, and where possible, analyzed with reference to pristine NTA solutions. AFM studies revealed that the addition of NTA into the starch biopolymer did not significantly affect surface roughness, with all examined films displaying similar Sq values ranging from 70.7 nm to 79.7 nm. Similarly, Young’s modulus measurements showed no significant changes after incorporating the 1,3,4-thiadiazole. Adhesion force and water contact angle assessments demonstrated that the films maintained high hydrophilicity (water wetting) across all examined films. Color analysis corroborated the anticipated trend, showing that increasing additive content resulted in decreased lightness and increased yellowness. Interestingly, however, while in polar isopropanol solvent at low concentration, NTA shows a typical single-band emission, centered at 410 nm and a slight enhancement of the band on the long-wavelength side around 530 nm, its incorporation into the biopolymer matrices results in the appearance of dual fluorescence signal with maxima at 430 and 530 nm. Concentration-dependence emission experiments, demonstrating that with even a slight increase of the amount of NTA in solution, an additional, weak long-wavelength emission band emerged within the spectral range corresponding to the intensive band in the biopolymer film, along with results of the performed quantum-chemical studies, including both the monomeric and aggregated (dimer and trimer) models, conclusively unveil that the dual fluorescence observed in starch/NTA films is due to molecular aggregation effects resulting in aggregation-induced emission. This study underscores the potential of NTA as an additive in biobased polymer films, furnishing them with new photophysical features without substantially altering their surface properties and thus enabling their extended applications.