Ancillary Ligand-Promoted Charge Transfer in Bis-indole Pyridine Ligand-Based Nickel Complexes.

There is growing demand for the utilization of first-row transition metal complexes in light-driven processes instead of their conventional noble metal counterparts due to the greater sustainability of first-row transition metal complexes. However, their major drawback is the ultrafast lifetime of the electronic excited states of these first-row transition metal complexes, particularly those of d square-planar systems such as Ni(II) complexes, wherein low-lying metal-centered (MC) states provide the deactivation pathway. To increase the excited-state lifetime and broaden their applications, it is important to develop sterically bulky, strong field ligands with low-lying π* orbitals and a highly σ-donating nature to augment the energy of MC states.

Competition among recombination pathways in single FAPbBr3 nanocrystals.

Single particle level microscopy of immobilized FAPbBr3 nanocrystals (NCs) has elucidated the involvement of different processes in their photoluminescence (PL) intermittency. Four different blinking patterns are observed in the data from more than 100 NCs. The dependence of PL decays on PL intensities brought out in fluorescence lifetime intensity distribution (FLID) plots is rationalized by the interplay of exciton- and trion-mediated recombinations along with hot carrier (HC) trapping.

The effect of Cu(I)-doping on the photoinduced electron transfer from aqueous CdS quantum dots.

The doping of CdS quantum dots (QDs) with Cu(I) disrupts electron-hole correlation due to hole trapping by the dopant ion, post-photoexcitation. The present paper examines the effect of such disruption on the rate of photoinduced electron transfer (PET) from the QDs to methyl viologen (MV2+), with implications in their photocatalytic activity. A significantly greater efficiency of PL quenching by MV2+ is observed for the doped QDs than for the undoped ones.

Modulation of fluorescence and phosphorescence of organoboron compounds from ortho-substituted phenolic Schiff bases by structural modification.

Light emission from organoboron compounds of Schiff bases is found to depend strongly on their chemical structure. Two of these compounds (OB1 and OB2), which contain a benzene ring between the Schiff base moieties, exhibit weak fluorescence in methanol, with marked viscosity dependence. Fluorescence lifetimes of these compounds are in picosecond timescale, as determined by femtosecond optical gating (FOG).

Recombination dynamics and manybody effect of excitons in large-area monolayer MoScapped with (111) NiO epitaxial layer.

CVD grown monolayer MoSfilms on c-sapphire substrates are vacuum annealed and capped with (111) NiO epitaxial films using pulsed laser deposition technique. Time, energy and polarization resolved optical techniques are used to understand the effect of capping on the excitonic properties of the monolayer MoS. It has been observed that trion contribution in the photoluminescence (PL) spectra increases after the capping, suggesting an enhancement of electron concentration in the conduction band.

Noninvasive and Contactless Characterization of Electronic Properties at the Semiconductor/Dielectric Interface Using Optical Second-Harmonic Generation.

Optical second-harmonic generation (SHG) is a reliable technique for probing material surface and interface characteristics. Here, we have demonstrated a non-destructive, contactless SHG-based semiconductor/dielectric interface characterization method to measure the conduction band offset and quantitatively evaluate charge densities at the interface in oxide and at the oxide surface. This technique extracts the interface-trapped charge type (donor/acceptor) and qualitatively analyzes the process-induced variation in interface states (), oxide, and oxide surface state density.

Unique Metal-Ligand Interplay in Directing Discrete and Polymeric Derivatives of Isomeric Azole-Carboxylate. Varying Electronic Form, C-C Coupling, and Receptor Feature.

This article dealt with the ruthenium and osmium derivatives of isomeric 1-indazole-3-carboxylic acid/2-indazole-3-carboxylic acid (HL1) and 1-benzimidazole-2-carboxylic acid (HL2) along with the π-acidic bpy (bpy = 2,2'-bipyridine) and pap (pap = 2-phenylazopyridine) co-ligands. It thus extended structurally authenticated monomeric ([(bpy)Ru(HL1)]ClO []ClO, (pap)Ru(L1) , (bpy)Os(L1) , (pap)Os(L1) , (bpy)Ru(L2) , (bpy)Os(L2) , and (pap)Os(L2) ) and dimeric ([(bpy)Ru(μ-L2)Ru(bpy)](ClO) [](ClO)) complexes. It also described modified L2' (L2' = 2,2'-bisbenzimidazolate)-bridged [(pap)Ru(μ-L2')Ru(pap)](ClO) [](ClO), where L2' was developed selectively with the {Ru(pap)} metal fragment via in situ intermolecular C-C coupling of the two units of decarboxylated benzimidazolate.

Single-Particle Dynamics of ZnS Shelling Induced Replenishment of Carrier Diffusion for Individual Emission Centers in CuInS Quantum Dots.

Insights into blinking and photoactivation of aqueous copper indium sulfide (CIS) quantum dots have been obtained using fluorescence correlation spectroscopy (FCS) and fluorescence lifetime correlation spectroscopy (FLCS). An unusual excitation wavelength-dependence of photoactivation/photocorrosion is manifested in an increase in the initial correlation amplitude (0) for λ = 532 nm, but a decrease for λ = 405 nm. This has been rationalized in terms of different contributions from surface-assisted recombination in the two cases.

Single particle level dynamics of photoactivation and suppression of Auger recombination in aqueous Cu-doped CdS quantum dots.

Cu-doped CdS quantum dots (QDs) have been synthesized in water using 3-mercaptopropionic acid (3-MPA) as the capping agent. They exhibit intense photoluminescence and excellent color tunability, unlike most of the QDs synthesized/dispersed in water so far. Complete characterization of these aqueous doped CdS QDs has been performed for the first time, along with a single particle level elucidation of their exciton dynamics using fluorescence correlation spectroscopy.

Interplay of conformational relaxation and hydrogen bond dynamics in the excited states of fluorescent Schiff base anions.

Time resolved fluorescence spectroscopic investigation of four Schiff base anions has established that their excited state dynamics is governed by several solvent properties: polarity, viscosity and hydrogen bond donating ability. With viscous protic solvents like glycerol, fluorescence lifetimes of anions have been found to be markedly longer than those in ethanol, implying that conformational relaxation of molecules plays a key role in their nonradiative relaxation. Surprisingly, the lifetimes in less viscous aprotic solvents, like acetonitrile, are found to be even longer.

Fluorescence monitoring of binding of a Zn (II) complex of a Schiff base with human serum albumin.

Zn (II) complexes of Schiff bases have potential applications in biomedical sciences as imaging agents, cancer therapeutics and diagnostics. Thus, it is important to understand their interaction with carrier proteins, like serum albumins. The present paper focuses on the binding interactions between Human serum albumin (HSA) and Znsalampy, making use of fluorescence spectroscopic techniques at ensemble as well as at single molecular level.

Microscopic Insights into the Mechanism of White Light Generation by Disruptive Interaction between Human Serum Albumin Amyloid Fibrils and Surfactant-AIEgen Nanorods.

Dimethyl-2,5-bis[4-(methoxyphenyl)amino] terephthalate (DBMPT) exhibits aggregation-induced enhancement of emission with Tween 40 and formation of nanorods with strong orange fluorescence. These nanorods disrupt fibrils of human serum albumin and lead to partial refolding of the protein, as monitored by circular dichroism and thioflavin T (ThT) fluorescence. The resultant milieu emits white light, the mechanism of which is explored in this study.

Exciton Dynamics in Colloidal CdS Quantum Dots with Intense and Stokes Shifted Photoluminescence in a Single Decay Channel.

CdS quantum dots (QDs), synthesized by a sol-gel method, exhibit significantly Stokes shifted bright photoluminescence (PL), predominantly from the trap states. Surprisingly, the PL decay at the emission maximum is single-exponential. This is an unusual observation for as-prepared QDs and indicates a narrow distribution in the nature of trap states.

3-aminoquinoline: a turn-on fluorescent probe for preferential solvation in binary solvent mixtures.

3-Aminoquinoline (3AQ) has been used as a fluorescent probe for preferential solvation in hexane-ethanol solvent mixtures. Results of the present experiment have been put into context by comparison with prior observations with 5-aminoquinoline (5AQ) as the probe. 3AQ exhibits a relatively small change of dipole moment (Δ= 2.

Photoluminescent Silica Nanostructures and Nanohybrids.

The complicated photophysics of wide variety of defects existing in silica (SiO ) layer of nanometer thickness determines widespread photoluminescence bands of Si/SiO based system as well as SiO nanoparticles (NPs) for their applications in photovoltaic and optoelectronic devices. This review attempts to summarize different photophysical processes in pure SiO NPs. Moreover, these NPs also act as scaffolds for various guest molecules to perform their specific functions.

Ultraslow Biological Water-Like Dynamics in Waterless Liquid Protein.

Fluorescence correlation spectroscopy and time-dependent fluorescence Stokes shift have been employed to elucidate dynamics in different time scales, ranging from picoseconds to nanoseconds, for human serum albumin, in its native and cationized forms as well as in the self-assembled complex of the cationized protein with the polymer surfactant (PS) glycolic acid ethoxylate lauryl ether. The effect of crowding in this complex, especially in the waterless condition, is of prime importance in this context. Excellent correlation of the dynamics with the structures, obtained by circular dichroism and Fourier transform infrared spectroscopy, has been observed.

Conformational and Solvation Dynamics of an Amyloidogenic Intrinsically Disordered Domain of a Melanosomal Protein.

The conformational plasticity of intrinsically disordered proteins (IDPs) allows them to adopt a range of conformational states that can be important for their biological functions. The driving force for the conformational preference of an IDP emanates from an intricate interplay between chain-chain and chain-solvent interactions. Using ultrafast femtosecond and picosecond time-resolved fluorescence measurements, we characterized the conformational and solvation dynamics around the N- and C-terminal segments of a disordered repeat domain of a melanosomal protein Pmel17 that forms functional amyloid responsible for melanin biosynthesis.

L-cysteine functionalized graphene quantum dots for sub-ppb detection of As (III).

Here, we report functionalized graphene quantum dots (GQDs) for the optical detection of arsenic at room temperature. GQDs with the fluorescence of three fundamental colors (red, green, and blue) were synthesized and functionally capped with L-cysteine (L-cys) to impart selectively towards As (III) by exploiting the affinity of L-cys towards arsenite. The optical characterization of GQDs was carried out using UV-vis absorption spectroscopy, Fourier transform infrared spectroscopy, and fluorescence spectrometry, and the structural characterizations were performed using transmission electron microscopy.

The Role of Hydrogen Bonding in the Preferential Solvation of 5-Aminoquinoline in Binary Solvent Mixtures.

5-Aminoquinoline (5AQ) has been used as a fluorescent probe of preferential solvation (PS) in binary solvent mixtures in which the nonpolar component is diethyl ether and the polar component is protic (methanol) or aprotic (acetonitrile). Hence, the roles of solvent polarity and solute-solvent hydrogen bonding have been delineated. Positive deviations of spectral shifts from a linear dependence on the concentration of the polar component, signifying PS, are markedly more pronounced in case of the protic solvent.

Recent Advances in Small Molecule-Based Intracellular pH Probes.

Intracellular pH plays an important role in many biological and pathological processes. Small-molecule based pH probes are found to be the most effective for pH sensing because of ease of preparation, high sensitivity, and quick response. They have many advantages such as small perturbation to the functions of the target, functional adaptability, cellular component-specific localization, etc.

From fluorogens to fluorophores by elucidation and suppression of ultrafast excited state processes of a Schiff base.

Strategies have been explored for developing strongly fluorescent species out of a weakly fluorescent Schiff base, 2-(((pyridin-2-ylmethyl)imino)methyl)phenol (salampy). The locally excited enolic state of salampy undergoes an intramolecular proton transfer with a time constant of 200 fs. The emissive cis keto state thus formed decays completely within 50 ps.

Intense photoluminescence from Cu-doped CdSe nanotetrapods triggered by ultrafast hole capture.

Brightly photoluminescent Cu-doped CdSe nanotetrapods (NTPs) have been prepared by a modified hot injection method. Their photoluminescence (PL) has a quantum yield of 38% and decays slowly over a few microseconds, while the PL in undoped NTPs has a rather small quantum yield of 1.7% and decays predominantly in tens of picoseconds, with a minor component in the nanosecond time regime.

Role of Solvent in Electron-Phonon Relaxation Dynamics in Core-Shell Au-SiO Nanoparticles.

Relaxation dynamics of plasmons in Au-SiO core-shell nanoparticles have been followed by femtosecond pump-probe technique. The effect of excitation pump energy and surrounding medium on the time constants associated with the hot electron relaxation has been elucidated. A gradual increase in the electron-phonon relaxation time with pump energy is observed and can be attributed to the higher perturbation of the electron distribution in AuNPs at higher pump energy.

Unique photoluminescence response of MoSquantum dots over a wide range of As (III) in aqueous media.

We report the solvothermal synthesis of MoSbased quantum dots (QDs) and the performance evaluation of bare QDs for the detection of aqueous As (III) oxidative state at room temperature and neutral pH over a vast range (0.1-1000 ppb). Concentration-dependent photoluminescence (PL) of the QDs enhances up to 50 ppb and then suppresses till 1000 ppb.