Red Shift Of Emission Maximum Research Articles

Exploring conformational changes in β-lactoglobulin (β-LG) induced by silibinin: A comprehensive analysis of polyphenol-protein interaction

This study investigates the comprehensive characterization of the interaction between β-lactoglobulin (β-LG) and Silibinin using various spectroscopic techniques. Fluorescence quenching experiments at different temperatures (298, 303, 308, and 313 K) revealed substantive interactions between β-LG and Silibinin, as indicated by a reduction in fluorescence intensity and a red shift in emission maxima. Further analysis, including Stern-Volmer quenching constants (KSV), bimolecular quenching rate constants (kq), and thermodynamic parameters demonstrated static quenching mechanism and strong binding affinities (Ka range: 0.138–1.483 × 105 M−1) between BLG-Silibinin complex. Thermodynamic study suggested positive enthalpy and entropy changes (ΔHo=43.31 kcal mol−1; ΔSo=164.33 cal mol−1 K−1), suggesting a spontaneous reaction with negative ΔGo values (-5.66 to -7.30 kcal mol−1). Forster resonance energy transfer (FRET) measurements confirmed optimal distances (r and Ro) for FRET occurrence, endorsing the static quenching mechanism. Molecular docking supported these findings, showcasing a 1:1 stoichiometric binding ratio for β-LG: Silibinin. The β-LG and Silibinin complex is primarily stabilized by hydrogen bonds and hydrophobic interactions. Molecular dynamics simulations over 200 ns highlighted stability in the β-LG-Silibinin complex, indicated by RMSD convergence, consistent RMSF values, and compactness illustrated by Rg. Conformational changes in β-LG upon Silibinin binding were further confirmed through UV-Vis absorption spectroscopy, FTIR, far-UV CD, synchronous fluorescence, and 3D fluorescence analyses. Functionally, the antioxidant capacity of β-LG increased after complexation with silibinin as quantified by DPPH assay. These results collectively depict the intricate network of interactions between Silibinin and β-LG, shedding light on the molecular details of their binding and offering insights into potential functional implications in biological contexts.

Fine-tuning photophysical properties in pyrene derivatives: Unravelling the impact of substitution patterns with incorporation of a strong electron-donating group

To investigate the impact of substitution patterns on the photophysical properties of pyrene derivatives, six novel pyrene derivatives A1-A6 were synthesised by directly coupling anthracene with pyrene units. The objective was to explore the influence of strong electron-donating groups and substitution patterns on their photophysical behaviour. Experimental and theoretical studies were conducted to analyse the photophysical properties of these compounds, revealing a clear dependence on the position of substitution within the pyrene core. Analysis of molecular orbitals revealed significant contributions from both pyrene and anthracene moieties, with deviations from typical electronic distributions attributed to the presence of electron-donating groups. The energy gap values remained consistent across derivatives, contrary to previous findings involving acceptor motif substitutions. Structural analyses indicated deviations from planarity with significant changes in angles upon excitation. The emission spectra of mono- and disubstituted pyrene derivatives predominantly exhibited a single broad maximum with slight shoulders in each solvent. However, the emission spectra of the tetrasubstituted compound (A6) displayed a vibrational structure with three maxima in all solvents, reminiscent of pyrene itself but red-shifted by approximately 30 nm. Furthermore, the central maximum for compound A6 was around 20 nm blue-shifted compared to the other compounds, although its shoulder at around 440 nm corresponded to a maximum observed in other pyrene derivatives. Typically, 1,3,6,8-tetrasubstituted pyrene derivatives, compared to their disubstituted analogues, exhibited red-shifted emission maxima associated with increased π-conjugation due to additional units on the pyrene core. A comprehensive analysis was performed on the absorption and emission spectra of the pyrene derivatives in solvents of various polarities and in the solid state. The fluorescence intensity was influenced by solvent polarity, with A6 showing limited sensitivity (similar quantum efficiency of approximately 45 % in all solvents). Moreover, the quantum yield decreases with the increasing number of anthracene substituents, being the lowest for tetrasubstituted A6. Bi-exponential decay and shorter lifetimes were observed for A1-A6 compared to known compounds, with quantum yields decreasing as solvent polarity increased. In the solid state, emission peaks shifted towards longer wavelengths, with A1 exhibiting the highest quantum yield attributed to steric hindrance. At low temperatures (77 K), emission spectra displayed redshifts, and longer lifetimes were observed. Spectrometric tests in THF/water mixtures indicated luminescence quenching at higher water fractions.

Preparation of AIEgen-based near-infrared afterglow luminescence nanoprobes for tumor imaging and image-guided tumor resection.

Fluorescence imaging represents a vital tool in modern biology, oncology and biomedical applications. Afterglow luminescence (AGL), which circumvents the light scattering and tissue autofluorescence interference associated with real-time excitation source, shows remarkably increased imaging sensitivity and depth. Here we present a protocol for the design and synthesis of AGL nanoprobes with an aggregation-induced emission (AIE) effect to simultaneously red shift and amplify the afterglow signal for tumor imaging and image-guided tumor resection. The nanoprobe (AGL AIE dot) is composed of an enol ether format of Schaap's agent and a near-infrared AIE fluorogen (AIEgen) (tetraphenylethylene-phenyl-dicyanomethylene-4H-chromene, TPE-Ph-DCM) to suppress the nonradiative dissipation pathway. Pre-irradiating AGL AIE dots with white light could generate singlet oxygen to convert Schaap's agent to its 1,2-dioxetane format, thus initializing the AGL process. With the aid of AIEgen, the AGL shows simultaneously red shifted emission maximum (from ~540 nm to ~625 nm) and enhanced intensity (by 3.2-fold), facilitating better signal-to-background ratio, imaging sensitivity and depth. Intriguingly, the activated AGL can last for over 10 days. Compared with conventional approaches, our method provides a new solution to concurrently red shift and amplify afterglow signals for better in vivo imaging outcomes. The preparation of AGL AIE dots takes ~2 days, the in vitro characterization takes ~10 days (less than 1 day if not involving afterglow kinetic profile study) and the tumor imaging and image-guided tumor resection takes ~7 days. These procedures can be easily reproduced and amended after standard laboratory training in chemical synthesis and animal handling.

Exploring the synergistic effect of aggregation and hydrogen bonding: a fluorescent probe for dual sensing of phytic acid and uric acid.

We synthesized an unoxidized bis-indolyl methane (BIM) derivative (probe 1) comprising of tetraphenylethylene (TPE) as the signalling moiety. The amphiphilic probe could form self-assembled nanoscopic aggregates in the aqueous medium. The emission of 1 in non-polar solvents originates from the LE state, while in polar solvents, it is dominated by TICT. Moreover, probe 1 exhibited a 'turn-on' fluorescence response for both uric acid (with a blue shift in emission maxima) and phytic acid (with a red shift in emission maxima). Therefore, the present system provides an exceptional opportunity to distinguish between phytic acid and uric acid by considering two different emission channels. Mechanistic investigations revealed that both H-bonding and electrostatic interactions between the probe and analytes could effectively cause restricted intramolecular rotations, leading to a turn-on response. Additionally, in the case of phytic acid, larger aggregates were observed with prominent CT characteristics. The change in the extent of charge transfer interaction in the formed adducts resulted in distinct fluorescence responses with phytic acid and uric acid. Furthermore, we explored the applicability of the present system in the screening of real-life samples, such as uric acid in urine samples and phytic acid in grains. The LOD for phytic acid and uric acid was found to be ∼5.48 nM and 10.4 nM, respectively. The quantitative nature of the system was confirmed, showing promising results in terms of recovery values (between 95.6% and 104.2%) and detection limits. Additionally, we also employed handy paper strips for the on-site monitoring of phytic acid and uric acid, thereby eliminating the need for complex instrumentation or trained technicians.

Visible Light Driven CO2 Photoreduction Using TiO2 Nanotube Arrays Embedded with Low Bandgap Carbon Nitride Nanoparticles

The extraordinary thermal and photochemical stability, superior charge transport, and tunable band positions of graphitic carbon nitride (g-CN), which is constituted of elements that are plentiful on Earth, renders g-CN an important semiconductor photocatalyst for heterogeneous catalysis [1,2]. Despite these advantages, carbon nitride-based semiconductors do not function effectively as freestanding photocatalysts or photoelectrodes due to a rapid carrier recombination rate and a slightly wide bandgap that only enables them to capture blue and UV photons [3,4]. Anodically formed TiO2 nanotube arrays (TNTAs) are semiconducting wide bandgap scaffolds with excellent photocatalytic properties due to the intrinsic orthogonalization of charge generation/transport and charge transfer processes. Herein, we use a novel in situ electrophoretic anodization to embed low bandgap carbon nitride nanoparticles (CNNPs) in the walls of titania nanotubes. The likelihood of the CNNPs leaching off the TNTA photoanode during photoelectrochemical processes was eliminated by encapsulating CN inside a TiO2 matrix. CNNPs were formed by the thermal condensation polymerization of carbon nitride utilizing citric acid and urea as the precursors, and exhibited some unusual properties, including a lower bandgap of 2.1 eV, a highly redshifted fluorescence emission maximum at 2.35 eV, surface carboxylate groups, and the emergence of unique structural characteristics corresponding to amorphous yet graphitic carbon [5]. In contrast to bulk g-CN, which has a C:N ratio of 0.75, the CNNPs possessed an elevated C:N ratio as high as 1.87 at the surface. The additional carbon was found to be both amorphous and graphitic, although the structural characteristics of g-CN were mostly unaffected, as validated by diffractometric and spectroscopic data. Even in the absence of a sacrificial agent, the CNNP@TNT nanocomposite demonstrated enhanced performance in sunlight-driven CO2 photoreduction. When compared to the freestanding TNT photocatalyst, the CO yield of photoreduction for the CN@TNT hybrid was more than three times higher. UV-filtered illumination of the CNNP@TNT heterojunction photocatalyst generated appreciable quantities of methane and CO (3.41 and 8.78 μmolg–1h–1 respectively). In situ electrophoretic anodization is an innovative approach to incorporate semiconductor quantum dots into TiO2 nanotubes or other electrochemically grown nanostructures.REFERENCES1. Kessler, F. K. et al., Nature Reviews Materials (2017) 2 (6), 1.2. Chaulagain, N. et al., ACS Applied Materials & Interfaces (2022) 14 (21), pp.24309-24320.3. Kumar, P. et al., Advanced Optical Materials (2020) 8 (4), Art. No. 1901275.4. Fu, J. et al., Advanced Energy Materials (2018) 8 (3), Art. No. 1701503.5. Alam, K.M. et al., Chemical Engineering Journal (2023) 456, Art. No. 141067.

Detection of multiple metal ions exclusively at bilayer interface: Does the nature of the membranous aggregates affect the sensitivity?

A pyrenylated fluorogenic probe has been designed that can detect heavy metal pollutants exclusively at the bilayer interface. The compound, due to extensive self-aggregation, showed no interaction with metal ions in the bulk solution phase. However, effective, nanomolar level detection of multiple metal ions, such as Cu2+, Hg2+, and Ni2+, etc. was achieved exclusively in vesicular aggregates. The optical response towards metal ions, including selectivity and sensitivity, largely depends on the microenvironment around the probe molecules, governed by the nature of the bilayer membrane (polarity, order, interfacial hydration, etc). In zwitterionic membranes, like DPPC, Hg2+-induced fluorescence quenching was witnessed along with red-shifted emission maxima. On the contrary, turn-off responses along with blue-shifted in maxima were noted upon addition of both Cu2+ and Ni2+ ions in the anionic phospholipid vesicle, DPPA. Moreover, an improvement in sensitivity was witnessed when the probe was embedded into phospholipid vesicles with a fluid-like liquid crystalline phase. The larger mobility of the probe molecules on the bilayer membrane, resulting in ease of reorganization, might be the probable reason for this.

Organic nanoparticles with tunable AIE derived from amino acids appended naphthalenediimide based amphiphiles

Fluorescent organic nanoparticles (FONPs) are unique cooperative manifestations of supramolecular self-aggregates and luminescent nanoparticles. In this work, we developed naphthalenediimide (NDI) based amphiphiles (NDI-1-9) having amino acids substitution from L-alanine to L-phenyl alanine to 3-(2-naphthyl)-L-alanine in absence and presence of alkyl spacer (C-6, C-11). Formation of self-aggregated spherical organic nanoparticles of ∼50 nm took place at and above 50 vol% water or methyl cyclohexane (MCH) in different binary solvent systems (DMSO/DMF-water, CHCl3-MCH) via J-aggregation. In case of NDI-1-3 (amino acids are directly connected to the NDI) self-assembled FONPs (MCH in CHCl3) exhibited aggregation-induced emission (AIE) through excimer formation. Red shift in the emission maxima were observed from 484 nm to 495 nm, and 590 nm, respectively with increasing π electron cloud at substituted donor from NDI-1 to NDI-3. Alongside, in case of aromatic amino acids substitution, FONPs of 6-amino caproic acid spacer containing NDI derivatives (NDI-5 and NDI-6) showed AIE at 505 nm and 545 nm (water in DMF/DMSO). Corresponding 11-amino undecanoic acid containing analogues (NDI-8 and NDI-9) showed AIE at 480 nm and 585 nm in CHCl3-MCH and DMF/DMSO-water. The multi colour emission from blue-green to yellow-orange with enrichment of π-electron cloud density in the side chain substitution of NDI was observed possibly due to the facilitated electron transfer at a lesser energy to the electron deficient NDI core that resulted in red shifted emission maxima. This was further clarified by regulating the availability of π-electrons of phenyl ring of NDI-2 by including electron withdrawing –NO2 and donating -OMe groups at the molecular backbone (NDI-2a and NDI-2b) that showed blue shifted (475 nm) and red shifted (570 nm) emission maxima with respect to NDI-2 (495 nm). However, increase in alkyl spacer length between side chain substitution and NDI core yielded relatively lower quantum yield presumably due to the impeded electron transfer.

PH-Switchable phenylalanine-templated copper nanoclusters: CO2 probing and efficient peroxidase mimicking activity.

Inter-cluster conversion through the strategic tuning of external stimuli and thereby modulation of the optical properties of metal nanoclusters (MNCs) is an emerging domain for exploration. Herein, we report the preparation of blue-emitting CuNCs using phenylalanine (Phe) as a template under acidic conditions (pH ∼ 4). The as-prepared CuNCs exhibit a sequential tuning of the photophysical properties upon varying the pH of the solution from pH ∼4 to pH ∼12. Blue-emitting CuNCs (B-CuNCs, λem = 410 nm) are systematically converted to cyan-emitting CuNCs (C-CuNCs, λem = 490 nm) with a large red-shifted emission maximum by 80 nm as a function of pH. Our present investigation delineates an unprecedented switchability of the photoluminescence (PL) properties of the CuNCs with the variations of the pH from pH ∼4 to pH ∼12. Both the Phe-templated CuNCs (B-CuNCs and C-CuNCs) were broadly characterized by various spectroscopic and morphological techniques. The X-ray photoelectron spectroscopy (XPS) studies reveal the presence of different oxidation states in the metallic core of B-CuNCs and C-CuNCs. These results in turn substantiate the pH-induced intercluster conversion of CuNCs through the substantial change in their core composition as well as valence states. Owing to the pH sensitivity, the CuNCs act as an efficient and highly sensitive probe for CO2, and quantitative estimation of the dissolved CO2 in the form of bicarbonate ions has been achieved through the enhancement of the PL intensity, wherein a very low value of the limit of detection (LOD) of ∼60 μM was obtained. Furthermore, we demonstrated that the CuNCs act as an efficient bio-catalyst with peroxidase mimicking enzymatic activity which has been investigated using OPD as a substrate under physiological conditions (pH ∼7.4 and temperature ∼37 °C). The mechanistic investigations confirmed that the oxidation of OPD mainly proceeds through the generation of hydroxyl radicals (˙OH). We hope the present investigations shed light on a multidimensional aspect of MNCs and uncover an upsurging recent interest in MNCs to act as an artificial enzyme.

Ion-specific bathochromic shifts: Simultaneous detection of multiple heavy metal pollutants via charge transfer interactions

An anthraimidazoledione-based colorimetric probe (1) has been developed to detect heavy metal pollutants in acetonitrile medium. Adding metal ions, such as Zn2+, Ni2+ and Co2+ induce ion-dependent redshifts in the metal-to-ligand charge transfer (MLCT) band. As a result, the almost colorless solution of1turned into green, yellow and red colors upon adding Zn2+, Ni2+, and Co2+ ions. On the other hand, the blue fluorescence of 1 is slightly quenched in the presence of Zn2+ ions, while the diminution is significant for Ni2+ ions. On the other hand, Co2+ ion results in the red-shift of emission maxima and quenching. Thus, we could observe faint cyan-colored fluorescence with Co2+ ions. The binding affinities for metal ions follow Irving–William’s order. At the same time, the colorimetric responses depend on the ionic radius, hydration enthalpy, coordination number, crystal field stabilization energies of the metal ions, etc. However, in the mixed aqueous environment, the ratiometric response was noticed only with Co2+ ions. Along with ratiometric color change, additions of metal ions result in an increase in both anodic and cathodic peak current along with shifts in the redox potential values. Further, the presence of residual Co2+ was determined in natural water samples.

Divergent Approach for Tris-Heteroleptic Cyclometalated Iridium Complexes Using Triisopropylsilylethynyl-Substituted Synthons.

Bis-heteroleptic cyclometalated iridium complexes of the form Ir(La)2(acac), where La is a substituted 2-phenylpyridine derivative and acac is an acetylacetonato ligand, are a useful class of luminescent organometallic complexes for a range of applications. Related tris-heteroleptic complexes of the form Ir(La)(Lb)(acac) offer the potential advantage of greater functionality through the use of two different cyclometalated ligands but are, in general, more difficult to obtain. We report the synthesis of divergent bis- and tris-heteroleptic triisopropylsilylethynyl-substituted intermediate complexes that can be diversified using a “chemistry-on-the-complex” approach. We demonstrate the methodology through one-pot deprotection and Sonogashira cross-coupling of the intermediate complexes with para-R-aryliodides (R = H, SMe, and CN). The photophysical and electrochemical behaviors of the resultant bis- and tris-heteroleptic complexes are compared, and it is shown that the tris-heteroleptic complexes exhibit subtly different emission and redox properties to the bis-heteroleptic complexes, such as further red-shifted emission maxima and lower extinction coefficients, which can be attributed to the reduced symmetry. It is demonstrated, supported by DFT and time-dependent DFT calculations, that the charge-transfer character of the emission can be altered via variation of the terminal substituent; the introduction of an electron-withdrawing cyano group in the terminal position leads to a significant red shift, while the introduction of an SMe group can substantially increase the emission quantum yield. Most notably, this convenient synthetic approach reduces the need to perform the often challenging isolation of tris-heteroleptic complexes to a single divergent intermediate, which will simplify access to families of complexes of the form Ir(La)(Lb)(acac).

Effect of cyano substituent on the functional properties of blue emitting Imidazo[1,2-a]pyridine derivatives

High fluorescence efficiency and balanced charge transportation in organic emitters are desirable characteristics for application in OLEDs. Generally, donor-acceptor compounds showing pronounced intramolecular charge transfer exhibit low fluorescence quantum yield. Here, we report D-A fluorophores containing CN-substituted 2-phenylimidazo[1,2-a]pyridine acceptor unit which exhibit good fluorescence characteristics. The positions of donors (triphenylamine/carbazole) and cyano substituents are respectively interchanged to get a series of isomers. All the fluorophores exhibit high fluorescence quantum yield (Фf≥ 0.70) and excellent thermal stability (Td10≥ 390 °C). A dye comprising triphenylamine unit at para-position of C2 phenyl ring exhibited red-shifted emission maxima with larger Stokes shift in the series. Moreover, all the isomers displayed excited-state solvatochromism attributable to the photo-induced intramolecular charge transfer between donors and cyano-imidazo[1,2-a]pyridine acceptor. Addition of the cyano group on imidazopyridine restrained the formation of aggregates in the solid-state and stabilized the lowest unoccupied molecular orbital. Among the all, doped devices constructed with 3 wt% of triphenylamine containing dye revealed excellent performance in the series with a maximum EQE of 6.9%, 2759 cd/m2 luminance, and CIE coordinates (0.16, 0.08) which is very close to the NTSC blue standard.

A fluorescent probe derived from benzofuranone for turn-on detection of sulfite in living cells and mice

A novel benzofuranone fluorescent probe, BFO-SFT, for monitoring sulfite in living cells and mice is described which operates over a wide pH range and exhibits a red-shifted emission maximum. The response of the probe BFO-SFT was relatively rapid (within 20 min) and exhibited a good linear correlation of 0–10 Eq (100 μM) with reliable accuracy (R2 = 0.9934). The probe also showed high sensitivity (Limit of detection = 152 nM) and selectivity. With low cytotoxicity, BFO-SFT was successfully applied into the biological imaging of sulfite in living MCF-7 cells and in BALB/C Nude mice.

Electronic Relaxation Dynamics in 2-Quinolinones with Extended Conjugation.

The 2-quinolinone family of molecules, also known as carbostyrils, have been proposed as light absorbing donor molecules in energy transfer based sensing schemes and as possible photocatalysts. Both of these applications make use of electronic excited states, but the photophysics of 2-quinolinones have not yet been examined closely. This study applies static and dynamic spectroscopy, with supporting density functional theory calculations, to reveal the electronic relaxation dynamics of a family of five 2-quinolinones with extended conjugated rings. These modifications lead to red-shifted absorbance and emission maxima, relative to unmodified 2-quinolinone. Optical excitation of these molecules with near UV light resulted in transitions with strong π → π* and HOMO → LUMO character. Time-correlated single photon counting measurements yielded fluorescence lifetimes ranging from 849.3 (±0.6) ps to 4.586 (±0.002) ns. Transient absorption spectroscopy revealed relaxation dynamics of the S1 excited state formed by photoexcitation at 350 nm, along with formation of a long-lived signal assigned as excited state absorption by a triplet excited state. Vibrational relaxation in the S1 state was also characterized in some compounds. Overlapping signals of S1 decay and triplet growth in the transient absorption data set could not be fully disentangled. These results demonstrate a highly competitive relaxation scheme following multiple simultaneous pathways, a promising situation for establishing chemical control of electronic relaxation in the 2-quinolinone family.

Pyrene Appended Free‐base, Phosphorus(V) and Gallium(III) Corroles and Their β,β′‐Linked Corrole Dimers: Synthesis, Photophysical and Electrochemical Properties

AbstractPyrene appended free‐base, phosphorus(V) and gallium (III) corrole conjugates were synthesized and characterized. Efficient β‐β′ dimerization of corroles was achieved by oxidation with p‐chloranil in moderate yield from their respective metallated corroles. The weak ground state electronic coupling between pyrene and corrole units was established by photophysical and electrochemical investigations. The fluorescence spectral studies showed a red shifted emission maximum for dimer with respect to their monomeric counterpart due to possible π‐conjugation and supported by the density functional theory (DFT). The electrochemical investigation revealed multiple oxidation associated with the corrole and pyrene centers.

Photophysical and molecular docking studies of photoinduced electron transfer (PET) and non-PET based fluorophores of acridinedione derivatives with a glycoprotein: Ovalbumin

Photophysical studies of resorcinol-based family of acridinedione (ADR) dyes with a glycoprotein, ovalbumin (OVA) were carried out in water. Addition of OVA to photoinduced electron transfer (PET) based dye (ADR1) resulted in a considerable red shift of emission maxima with a slight increase in the fluorescence intensity, whereas no significant variation in the fluorescence intensity or shift of emission maxima results in the case of a non-PET dye. Fluorescence lifetime studies illustrates that the PET lifetime component enhances by several fold on the introduction of OVA which is accompanied with the formation of multi lifetime components in the aqueous phase of varying distribution as observed in well-known globular protein, bovine serum albumin (BSA). Interestingly, a decrease in the fluorescence lifetime of non-PET dye (ADR2) with the evolution of more than one distinct lifetime species results with OVA. This behaviour ascertains the presence of at least two different micro environment of dye residing in aqueous phase on the addition of OVA. The introduction of OVA induces the formation of several distinguishable micro environments around the close vicinity of the dye molecule that are subjected to various binding forces. Further, the dye bound to several amino acid residues through conventional and non-conventional hydrogen-bonding interactions accompanied with hydrophobic interactions, pi-pi, pi-alkyl interactions and weak van der Waals forces also coexist. The variation in binding energies of various dye-OVA conformations are established from molecular docking (MD) techniques. The combination of docking techniques validates and authenticates the origin of multi decay characteristics of dye-OVA complex that correlates dye bound to different binding sites in protein. A combined approach of fluorescence techniques along with MD methods and Isothermal Calorimetric Titration (ITC) studies provides an excellent approach in determining the nature of interaction and binding stability of dye-protein system in a micro heterogeneous environment.

Enhanced brightness and electron affinity of terrylenediimide with sulfone-bridged substituents on the bay region.

Terrylenediimide with electron-withdrawing groups (TDI4SF) was synthesized by the attachment of sulfone substituents on the bay region of terrylenediimide. The electron-withdrawing sulfone groups enhance the electron affinity, reduce the LUMO level to -4.37 eV, and endow TDI with excellent anti-oxidation ability. With sulfone substituents, TDI4SF has a red-shifted emission maximum with a peak at 702 nm and high photoluminescence quantum yield.

Density Functional Studies on Photophysical Properties of Boron-Pyridyl-Imino-Isoindoline Dyes: Effect of the Fusion.

In this work, to make out the aryl-fusion effect on the photophysical properties of boron-pyridyl-imino-isoindoline dyes, compounds 1–5 were theoretically studied through analyses of their geometric and electronic structures, optical properties, transport abilities, and radiative (kr) and non-radiative decay rate (knr) constants. The highest occupied molecular orbitals of aryl-fused compounds 2–5 are higher owing to the extended conjugation. Interestingly, aryl fusion in pyridyl increases the lowest unoccupied molecular orbital (LUMO) level, while isoindoline decreases the LUMO level; thus, 4 and 5 with aryl fusion both in pyridyl and isoindoline exhibit a similar LUMO to 1. Compounds 4 and 5 show relatively low ionization potentials and high electron affinities, suggesting a better ability to inject holes and electrons. Importantly, the aryl fusion is conducive to the decrease of kIC. The designed compound 5 exhibits a red-shifted emission maximum, low λh, and low kIC, which endow it with great potential for applications in organic electronics. Our investigation provides an in-depth understanding of the aryl-fusion effect on boron-pyridyl-imino-isoindoline dyes at molecular levels and demonstrates that it is achievable.

Triarylboron/Triarylamine-Functionalized 2,2'-Bipyridine Ligands and Their Copper(I) Complexes.

We report herein three new either -BMes2 (Mes = mesityl) or -NPh2 group-functionalized 2,2'-bipyridine ligands-4,4'-(p-BMes2-phenyl-C≡C)2-2,2'-bpy (BB-bpy), 4-(p-BMes2-phenyl-C≡C)-4'-(p-NPh2-phenyl-C≡C)-2,2'-bpy (BN-bpy), and 4,4'-(p- NPh2-phenyl-C≡C)2-2,2'-bpy (NN-bpy)-along with their heteroleptic copper(I) complexes Cu(L)(PPh3)2(BF4) (L = BB-bpy, BN-bpy, and NN-bpy, respectively). The electron-donor and -acceptor units are connected to the bipyridine core via acetylene linkers. The incorporation of acetylene linkers decreases the dihedral angle between the bridging phenyl and pyridine rings, resulting in a nearly coplanar geometry of the ligands. All free ligands display temperature-dependent luminescence changes, which may be explained by the twisted intramolecular charge-transfer mechanism. Binding with Cu(I) results in significantly red-shifted emission maxima for the heteroleptic complexes Cu(NNbpy)(PPh3)2(BF4) [Cu(NNbpy)] and Cu(BNbpy)(PPh3)2(BF4) [Cu(BNbpy)] relative to those of the free ligands. The electronic and photophysical properties of all compounds were investigated by electrochemical, absorption, and emission spectroscopic analyses as well as density functional theory calculations.

Fluorescence spectroscopy of ancient sedimentary organic matter via confocal laser scanning microscopy (CLSM)

Fluorescence spectroscopy via confocal laser scanning microscopy (CLSM) was used to analyze ancient sedimentary organic matter, including Tasmanites microfossils in Devonian shale and Gloecapsomorpha prisca (G. prisca) in Ordovician kukersite from North American basins. We examined fluorescence emission as a function of excitation laser wavelength, sample orientation, and with respect to location within individual organic entities and in transects across bedded organic matter. Results from spectral scans of the same field of view in Tasmanites with different laser lines showed progressive red-shift in emission maxima with longer excitation wavelengths. This result indicates steady-state Tasmanites fluorescence emission is an overlapping combination of emission from multiple fluorophore functions. Stokes shift decreased with increasing excitation wavelength, further suggesting the presence of multiple fluorophore functions with different S1 → S0 transition energies. This observation also indicates that at longer excitation wavelengths, less absorbed light energy is dissipated via collisional transfer than at shorter excitation wavelengths and may suggest fewer polar functions are preferentially absorbing. Confirming earlier results, emission spectra observed from high fluorescence intensity regions (fold apices) in individual Tasmanites are blue-shifted relative to emission from other locations in the same microfossil. We suggest high intensity emission is from photoselective alignment of polarized excitation with the fluorophore absorption and emission transition moment. The blue shift observed in regions of high intensity emission may be due to relative absence or realignment of polar species, e.g., bridging ether or ester functions, although variations in O abundance could not be confirmed with preliminary time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis. Tasmanites occurring in consolidated sediments are flattened from original spherical morphology and, in optical microscopy, this burial deformation results in generally parallel extinction (strain-influenced) and positive elongation. The deformation also induces fluorescence anisotropy observed as variations in emission wavelength when individual Tasmanites are measured from their long axis parallel to bedding, whereas this effect is absent in bedding-normal view. Transects from G. prisca-rich source layers into adjacent reservoir layers show decrease in fluorescence intensity and spectral red-shift (increase in full-width half-maximum with increasing red portion of the half-width). These results may suggest an increase in fluorescence quenching across the source-to-reservoir transition zone, consistent with an increase in aromaticity following petroleum expulsion and migration. These observations are supported by increasing reflectance values measured across similar micro-scale transects. Our results highlight the applicability of CLSM as a broad and under-utilized approach for the characterization of sedimentary organic matter and are discussed with perspective toward petroleum processes and thermal indices research.

Optical insights of indium-doped β–Ga2O3 nanoparticles and its luminescence mechanism

Undoped and In3+ doped β–Ga2O3 nanoparticles have been synthesized at 900 °C using polyol-mediated technique. The effect of Indium dopant on structural, morphological and photoluminescence properties of β–Ga2O3 nanoparticles were investigated in detail. X-ray diffraction patterns demonstrate the monoclinic crystalline structure and indium doping leads to substantial changes in the lattice parameters of β–Ga2O3 nanoparticles. The scanning electron microscope (SEM) images showed reduction in the particle size on doping as due to grain growth inhibition effect. Observed red shift in emission maxima and is increasing with increased In3+ content. Indeed, the shift changes are due to the interactions between donors and acceptors, which are identified as donor–acceptor pair recombination. To understand the red-shift phenomena, we performed time-resolved and steady-state spectroscopic studies for the doped samples. The red shift in the emission maxima of Indium-doped samples was further confirmed with the band gap measurements using absorption spectroscopy and ab initio calculation results.