Multifunctional Dy2NiMnO6/Reduced Graphene Oxide Nanocomposites and Their Catalytic, Electromagnetic Shielding, and Electrochemical Properties.

Multifunctional nanocomposites have shown great interest in clean energy systems and environmental applications in recent years. Herein, we first reported the synthesis of Dy2NiMnO6 (DNMO)/reduced graphene oxide (rGO) nanocomposites utilizing a hybrid approach involving sol-gel and solvothermal processes. Subsequently, we investigated these nanocomposites for their applications in catalysis, electromagnetic interference shielding, and supercapacitors. A morphological study suggests spherical-shaped DNMO nanoparticles of an average size of 382 nm that are uniformly distributed throughout the surface without any agglomeration. The as-prepared nanocomposites were used as catalysts to investigate the catalytic reduction of 4-nitrophenol in the presence of NaBH4. DNMO/rGO nanocomposites demonstrate superior catalytic activity when compared with bare DNMO, with the rate of reduction being influenced by the composition of the DNMO/rGO nanocomposites. In addition, novel multifunctional DNMO/rGO was incorporated into polyvinylidene difluoride (PVDF) to develop a flexible nanocomposite for electromagnetic shielding applications and exhibited a shielding effectiveness of 6 dB with 75% attenuation at a frequency of 8.5 GHz compared to bare PVDF and PVDF-DNMO nanocomposite. Furthermore, the electrochemical performance of DNMO/rGO nanocomposites was investigated as an electrode material for supercapacitors, exhibiting the highest specific capacitance of 260 F/g at 1 A/g. These findings provide valuable insights into the design of DNMO/rGO nanocomposites with remarkable performance in sustainable energy and environmental applications.

Enhancing the PEC Efficiency in the Perspective of Crystal Facet Engineering and Modulation of Surfaces.

Generation of hydrogen is one of the most promising routes to harvest solar energy for its sustainable utilization. Among different routes, the photoelectrochemical (PEC) process to split water using solar light to produce hydrogen is the green method to generate hydrogen. The sluggish kinetics through complicated pathways makes the oxygen evolution reaction the rate limiting step of the overall water splitting process. Therefore, development of an efficient photoanode for the sustainable oxidation of water is most challenging in an efficient overall PEC water splitting process. The low solar to hydrogen conversion efficiency arises from the slow surface kinetics, poor hole diffusion, and fast charge recombination processes. There have been strategies to improve catalytic performances through the removal of such detrimental effects. The generation of engineered surfaces is one of the important strategies recently adopted for the enhancement of the catalytic efficiencies. The present review has been focused on the discussion of engineered surfaces using crystal facet engineering, protective surface layer, passivation using the atomic layer deposition (ALD) technique, and cocatalyst modified surfaces to enhance the catalytic efficiency. Some of the important parameters defining catalyst performance are also discussed at the beginning of the review.

Bismuth Vanadate and 3D Graphene Composite Photoanodes for Enhanced Photoelectrochemical Oxidation of Water.

Bismuth vanadate (BiVO4) has been one of the most promising photoanodes for the photoelectrochemical (PEC) water oxidation process. Efforts are still on to overcome the drawbacks of this photoanode to enhance the catalytic efficiency and improve the stability. In the present work, three-dimensional graphene (3D-G) was incorporated inside the BiVO4 matrix, primarily to improve the conductivity of the material. The photoanodes are fabricated with the incorporation of a SnO2 heterojunction and application of cobalt borate (Co-Bi) as a cocatalyst. The incorporation of 3D-G has enhanced the photocurrent from 0.72 o 1.21 mA cm-2 in ITO/SnO2/BiVO4 and ITO/SnO2/3D-G-BiVO4 materials; the photocurrent has been improved from 0.89 to 1.52 mA cm-2 in ITO/SnO2/BiVO4/Co-Bi and ITO/SnO2/3D-G-BiVO4. Semiconductor properties are evaluated from the Mott-Schottky measurements, and the charge transfer and transport kinetics of the PEC process are measured from several photoelectrochemical investigations. Both the charge transport and the charge transfer efficiencies are enhanced upon inclusion of 3D-G into the catalyst system. The lifetime of the charge carrier is observed to be increased. The decrease in the decay kinetics of the holes, enhancement in the open-circuit photovoltage (OCPV), and the resulting modulation of the surface states are responsible for the enhancement in the surface charge transfer process due to the inclusion of 3D-G into the catalytic system. Therefore, the additional role of 3D-G in the modulation of the surface states and release of the Fermi level pinning has made the band alignment between the semiconductor and the analyte better, which resulted in enhanced catalytic performance in the photoelectrochemical oxidation of water.

Fabrication of Alkaline Electrolyzer Using Ni@MWCNT as an Effective Electrocatalyst and Composite Anion Exchange Membrane.

Here, we report the synthesis of nickel nanoparticles thermally encapsulated in multiwalled carbon nanotubes (MWCNTs) and its utility in alkaline water splitting by combining with composite thermoset anion-exchange membrane. Ni@MWCNT displayed both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). It provided 10 mA cm-2 current density at an overpotential of 300 mV for OER and 254 mV for HER on a glassy carbon electrode, respectively. Base-catalyzed N-methly-4-piperidone-formaldehyde-based prepolymer was grafted on to poly(vinyl alcohol) and cross-linked via thermal annealing followed by quaternization using methyl iodide to obtain thermoset anion exchange membrane (NMPi). Composite NMPi membranes were synthesized using additives tetraethyl orthosilicate (TEOS) and zirconium oxychloride. The water splitting performance on the fabricated membrane electrode assembly was tested and compared with commercially available Neosepta membrane. The obtained faradic efficacy of the water splitting was 94.33% for ZrO2-NMPi membrane followed by 80.23%, 77.70%, and 65.10% for SiO2-NMPi, NMPi, and Neosepta membranes, respectively. The best membrane ZrO2-NMPi achieved maximum current density of ∼0.776 A cm-2 in 5 M KOH electrolyte at 80 °C and 2 V applied constant voltage. The excellent alkaline stability of MEA indicates its potential utility in hydrogen generation applications.

γ-Ray-Assisted Synthesis of a Pt-Sn Bimetallic Composite Loaded on Graphene-Graphitic Carbon Nitride Hybrid: A Cocktail Electrocatalyst for the Methanol Oxidation Reaction.

The composite of Pt with transition metals is viewed as the most promising anode material for direct methanol fuel cell (DMFC) applications. Besides the decrease in the Pt loading, these multimetallic structures help in circumventing CO poisoning issues associated with a Pt catalyst. Herein, we prepared and loaded Pt-Sn bimetallic nanoparticles on an electron-rich and stable substrate consisting of graphitic nitride (GCN) and graphene oxide (GO)/reduced graphene oxide (r-GO) hybrid composites. The γ-radiolysis method was employed for coreduction of metal salts to deposit the binary composite of metal nanoparticles over the substrates. These structures were tested as the anode material for the methanol oxidation reaction (MOR). Among various possible combinations, Pt-Sn-loaded rGO-GCN (Pt-Sn/rGO-GCN) demonstrated the current density of ca. 2.4 A/mgPt. To the best of our knowledge, this value is among the highest ones, reported for similar systems in the acidic pH. Furthermore, these composites demonstrated excellent stability in the repeated cycle test. The improved performance is associated to the plenty of -OH groups provided by the Sn counterpart and a large number of adsorption sites from the electron-reached GCN counterpart.

An electrochemical technique for fabrication of Mn-54 sources towards characterization of gamma counting nuclear instruments.

Long lived sealed radioactive sources are used for the energy calibration and efficiency determination of counting systems used in the nuclear sector. Using a sulphate bath, a facile electrochemical method was developed by electrodeposition of 54Mn on 5 mm (φ) stainless steel substrates for the preparation of 54Mn sources for such uses. Inactive sources prepared under suitable experimental parameters characterized by XRD revealed that manganese is deposited in oxide form. SEM and EDS analyses of electrodeposited surfaces confirmed uniform distribution of elements and the absence of fractures, flaws, and spatial variations. Cyclic voltammetry (CV) scans provided information about the electrochemical processes involved in the deposition process. Uniform distribution of radioactivity on surface of source was ascertained by autoradiography. Swipe tests of the encapsulated sources confirmed negligible removable surface contamination. The 54Mn sources containing up to 185KBq of 54Mn on stainless steel discs were prepared. These sources along with other longer lived sources were supplied to various users as a package of radiation sources for characterization of gamma counting systems over a wide energy range.

Probing the interaction of anti-HIV drug Darunavir with dsDNA and HSA using electrochemical and spectroscopic measurements.

Investigation of electrochemical and spectroscopic characteristics of anti-human immunodeficiency virus (HIV) drug provides important information related to the efficacy of the drug in relation with its interaction with several important biomolecules. In the present investigation we have developed an electrochemical and spectroscopic method for the detection of anti-HIV drug Darunavir (DRV) using the carbon paste as the working electrode. The analytical method has generated the detection limit of 1.86 µM (S/N = 3). The electrochemical investigations have also been carried out for the exploration of the interaction of DRV with double stranded deoxyribose nucleic acid DNA (dsDNA) and human serum albumin (HSA). Electrochemical investigations were supported from the spectroscopic measurements in evaluating the interaction. The results obtained from voltammetric and spectroscopic experiments shows strong interaction between the drug and the macromolecules. It has been observed that DRV forms strong complexes with HSA and dsDNA with the formation constants of 2.7 × 104 and 4.2 × 104 M-1 respectively. The formation constants are varied with the pH of the solution, which leads to the assertion of the mechanism of the interaction between DRV and dsDNA.

Probing the interaction of ciprofloxacin and E. coli by electrochemistry, spectroscopy and atomic force microscopy.

Under the present investigation, effect of ciprofloxacin (CIP) on Escherichia coli has been investigated using electrochemical, spectroscopic and atomic force microscope (AFM) measurements. Investigation reveals the interaction pattern of CIP with E. coli. The CIP essentially interacts with the outer membrane protein F (OmpF), the formation constant of the complex forms between CIP and the OmpF active sites over E. coli is obtained as log Kf of 12.1. Spectroscopic measurements are carried out, which supports the electrochemical measurements on the interaction between CIP and E. coli, at a higher concentration, CIP induces lysis of the E. coli cell membrane. Spectroscopic investigations further reveals that the FeS containing proteins present inside the E. coli cells released out through the ruptured cell membrane of E. coli. Different degrees of detrimental effects on E. coli has been observed when exposed to different concentrations of the drugs. The microscopic images obtained from the AFM scans of E. coli in presence of CIP shows deformation of the E. coli cell wall and its rupture with increasing concentrations of CIP.

Insight into the PEC and interfacial charge transfer kinetics at the Mo doped BiVO4 photoanodes.

BiVO4 is a promising photoanode material for the photoelectrochemical (PEC) oxidation of water; however, its poor charge transfer, transport, and slow surface catalytic activity limit the expected theoretical efficiency. Herein, we have investigated the effect of Mo doping on SnO2 buffer layer coated BiVO4 for PEC water splitting. SnO2 and Mo doped BiVO4 layers are coated with layer by layer deposition through a precursor solution based spin coating technique followed by annealing. At 5% doping of Mo, the sample (SBM5) shows a maximum current density of 1.65 mA cm-2 at 1.64 V vs. RHEl in 0.1 M phosphate buffer solution under AM 1.5 G solar simulator, which is about 154% improvement over the sample without Mo (SBM0). The significant improvement in the photocurrent upon Mo doping is due to the improvement of various bulk and interfacial properties in the materials as measured by UV-vis spectroscopy, electrochemical impedance spectroscopy (EIS), Mott-Schottky analysis, and open-circuit photovoltage (OCPV). The charge transfer kinetics at the BiVO4/electrolyte interface are investigated to simulate the oxygen evolution process in photoelectrochemical water oxidation in the feedback mode of scanning electrochemical microscopy (SECM) using 2 mM [Fe(CN)6]3- as the redox couple. SECM investigation reveals a significant improvement in effective hole transfer rate constant from 2.18 cm s-1 to 7.56 cm s-1 for the hole transfer reaction from the valence band of BiVO4 to [Fe(CN)6]4- to oxidize into [Fe(CN)6]3- with the Mo doping in BiVO4. Results suggest that Mo6+ doping facilitates the hole transfer and suppresses the back reaction. The synergistic effect of fast forward and backward conversion of Mo6+ to Mo5+ expected to facilitate the V5+ to V4+ which has an important step to improve the photocurrent.

177Lu-labeled cyclic Asn-Gly-Arg peptide tagged carbon nanospheres as tumor targeting radio-nanoprobes.

This study explores the potential of 177Lu-labeled carbon nanospheres as radio-nanoprobes for molecular imaging and therapy. The carboxyl functionalized surface of carbon nanospheres (CNS) was conjugated with [Gly-Gly-Gly-c(Asn-Gly-Arg)], G3-cNGR peptide through amide bond for targeting tumor vasculature and with [2-(4-Aminobenzyl)-1,4,7,10-tetraazacyclododecane tetraacetic acid], p-NH2-Bz-DOTA for chelation with 177Lu. The nanosphere-peptide conjugate, DOTA-CNS-cNGR, was characterized by dynamic light scattering and zeta potential measurements, IR and UV experiments and did not show any in vitro cytotoxicity. The pharmacokinetics and biodistribution of 177Lu-labeled nanosphere-peptide conjugate, 177Lu-DOTA-CNS-cNGR was compared with 177Lu-DOTA-CNS (without the peptide) as well as with 177Lu-DOTA-cNGR (without carbon nanospheres). The radiolabeled nanosphere-peptide conjugate exhibited higher tumor accumulation than nanosphere-free radiolabeled peptide. The accumulation of the two radiolabeled probes in the tumor reduced to half during blocking studies with unlabeled G3-cNGR peptide. 177Lu-DOTA-CNS exhibited higher tumor uptake than 177Lu-DOTA-CNS-cNGR but rapid clearance of the latter nanoprobe from non-target organs resulted in significantly higher (p < 0.05) tumor-to-blood and tumor-to-muscle ratios at 24 and 48 h p.i. It is evident from this study that carbon nanospheres conjugated to specific vectors shall form an important part of targeted radionanomedicine in future.

Incorporation of Carbon Quantum Dots for Improvement of Supercapacitor Performance of Nickel Sulfide.

A facile hydrothermal method is adopted for the synthesis of hierarchical flowerlike nickel sulfide nanostructure materials and their composite with carbon quantum dot (NiS/C-dot) composite. The composite material exhibited good performance for electrochemical energy-storage devices as supercapacitor with a specific capacity of 880 F g-1 at a current density of 2 A g-1. The material remained stable up to the tested 2000 charge-discharge cycles. Carbon quantum dots of size 1.3 nm were synthesized from natural sources and the favorable electronic and surface property of C-dots were utilized for improvement of the supercapacitor performance of NiS. The results from Tafel analysis, double-layer capacitance, and the impedance measurement reveal that the incorporation of C-dots inside the NiS matrix has improved the charge-transfer process, which is mainly responsible for the enhancement of the supercapacitive property of the composite materials.

Electrochemical and SECM Investigation of MoS2/GO and MoS2/rGO Nanocomposite Materials for HER Electrocatalysis.

Development of advanced materials for electrocatalytic and photocatalytic water splitting is the key in utilization of renewable energy. In the present work, we have synthesized MoS2 nanoparticles embedded over the graphene oxide (GO) and reduced graphene oxide (rGO) layer for superior catalytic activity in the hydrogen evolution process (HER). The nanocomposite materials are characterized using different spectroscopic and microscopic measurements. A Tafel slope of ∼40 mV/decade suggested the Volmer-Heyrovsky mechanism for the HER process with MoS2/GO composite as the catalyst, which indicated that electrochemical desorption of hydrogen is the rate-limiting step. The small Tafel slope indicates a promising electrocatalyst for HER in practical application. MoS2/GO composite material has shown superior catalytic behavior compared to that of MoS2/rGO composite material. The HER catalytic activity of the catalysts is explored using scanning electrochemical microscopy (SECM) using the feedback and redox competition mode in SECM. The activation energy for HER activity was calculated, and the values are in the range of 17-6 kJ/mol. The lower value of activation energy suggested faster HER kinetics.

Effect of Substrates on the Photoelectrochemical Reduction of Water over Cathodically Electrodeposited p-Type Cu2O Thin Films.

In this study, we demonstrate development of p-Cu2O thin films through cathodic electrodeposition technique at constant current of 0.1 mA/cm(2) on Cu, Al, and indium tin oxide (ITO) substrates from basic CuSO4 solution containing Triton X-100 as the surfactant at 30-35 °C. The optical and morphological characterizations of the semiconductors have been carried out using UV-vis spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy. The band gap energy of ∼2.1 eV is recorded, whereas SEM reveals that the surface morphology is covered with Cu2O semiconductors. XRD analyses confirm that with change in substrate, the size of Cu2O "cubic" crystallites decreases from ITO to Al to Cu substrates. Photoelectrochemical characterizations under dark and illuminated conditions have been carried out through linear sweep voltammetry, chronoamperometry and electrochemical impedance spectroscopic analysis. The photoelectrochemical reduction of water (H2O → H2) in pH 4.9 aqueous solutions over the different substrates vary in the order of Cu > Al > ITO. The highest current of 4.6 mA/cm(2) has been recorded over the Cu substrate even at a low illumination of 35 mW/cm(2), which is significantly higher than the values (2.4 mA/cm(2) on Au coated FTO or 4.07 mA/cm(2) on Cu foil substrate at an illumination of 100 mW/cm(2)) reported in literature.

Electrochemically deposited gold nanoparticles on a carbon paste electrode surface for the determination of mercury.

An electrochemical method was developed for the determination of Hg at ultratrace levels using an Au nanoparticle (AuNP) array modified carbon paste electrode (CPE) by anodic stripping voltammetry. Scanning electron microscopy measurements imaged the size and shape of AuNPs on the CPE substrate; it was possible to tune the size and the NP density by changing the deposition time and medium. Electrochemical characterization of the AuNP modified CPE was carried out using cyclic voltammetry and electrochemical impedance measurements. Interferences due to some commonly occurring metal ions and surfactants on the stripping peak of Hg were also investigated. The 3σ detection limit for Hg using the AuNP modified electrode was as 0.24 µg/L. This method was applied to determine Hg in soil samples.

Tuning of intermolecular electron transfer reaction by modulating the microenvironment inside copolymer-surfactant supramolecular assemblies.

Photoinduced intermolecular electron transfer (ET) dynamics between various 7-aminocoumarin acceptors and N,N-dimethylaniline (DMAN) donor has been studied in copolymer-surfactant supramolecular assemblies prepared in aqueous 1% P123 triblock copolymer micellar solution with varying concentration of surfactants (sodium dodecyl sulfate (SDS), cetyl trimethyl ammonium chloride (CTAC), and triton-X-100 (TX100)). The aim of the present study is to modulate the reaction environment, especially the degree of micellar hydration inside the P123 micelle by the addition of the surfactants, which can modulate the ET reaction through the changes in the ET rates and the reaction exergonicity. Within the limited surfactant to copolymer molar ratios (n) used in the present study, fluorescence spectroscopy, dynamic light scattering (DLS), and small-angle neutron scattering (SANS) investigations indicate that the copolymer-surfactant supramolecular assemblies retain their micellar structure, although the micellar size gradually decreases with n. The redox potentials of the electron donor and acceptors are also found to change with n, although the extent of the effect is different for SDS, CTAC, and TX100 cosurfactants. In the presence of CTAC, the estimated exergonicity (-ΔG(0)) of the ET reaction is found to increase with an increase in n compared with that in pure P123, whereas it decreases marginally with SDS and remains almost the same for TX100. Substantial quenching of coumarin fluorescence is observed in the presence of DMAN in all copolymer-surfactant micellar aggregates because of ET reaction. The ET rate is seen to increase gradually with an increase in SDS and CTAC concentration in the supramolecular assembly, although it remains unaffected on the addition of TX100. The increased ionic strength in the Corona region of the copolymer-surfactant supramolecular aggregates due to the addition of the ionic surfactants has been envisaged for the increase in the ET rates. A correlation of the quenching rate constants with the free-energy changes (ΔG(0)) of the ET reactions shows the typical bell-shaped curve as predicted by Marcus outersphere ET theory. A substantial shift along the exergonicity axis (~0.3 eV) for the appearance of the Marcus correlation is observed in some cases, although the extent of such shift depends on both the nature of the cosurfactant and the amount of cosurfactant used in the copolymer-surfactant supramolecular assembly. Therefore, these preliminary results suggest a possibility of not only modulating the ET rates but also tuning the appearance of Marcus inversion along the exergonicity scale by suitably tuning the reaction environment inside the copolymer-surfactant supramolecular assemblies with a relatively more hydrophilic cosurfactant.

Ultrafast electron transfer dynamics in micellar media using surfactant as the intrinsic electron acceptor.

Ultrafast photoinduced intermolecular electron transfer (ET) dynamics involving 7-aminocoumarin derivatives as electron donor and pyridinium moiety of surfactant molecules in cetylpyridinium chloride (CPC) micelle as electron acceptor has been investigated to understand the role of separation and orientation of reactants on micellar ET reactions. Unlike in noninteracting micelles (like Triton-X-100, sodium dodecyl sulfate, dodecyltrimethylammonium bromide, etc.), where surfactant-separated donor-acceptor pairs are understood to give the ultrafast ET component with the shortest time constant in the range of approximately 4 ps, in CPC micelles with pyridinium moiety as the intrinsic acceptor the ultrafast ET component is found to be in the subpicosecond time scale (of around 240 fs). This time scale is very similar to the values reported in the cases of ultrafast ET reactions involving coumarin dyes in electron-donating solvents. The ultrafast ET times in CPC micelles are significantly faster than the diffusive solvation dynamics in the micellar media. Correlation of the observed ET rates in the present cases with the free-energy changes of the reactions shows the inverse-bell-shaped correlation, predicted by Marcus ET theory. Interestingly, the onset of the Marcus inversion appears at a relatively lower exergonicity, which is attributed to the nonequilibrium solvent configuration during the ultrafast ET reaction, as envisaged from two-dimensional ET (2DET) model. Along with the ultrafast ET component, there are also slower ET components in these systems, which are attributed to those close-contact donor-acceptor populations in the micelles that have relatively weaker electronic coupling due to improper orientation of the interacting donor-acceptor pairs. The present results suggest that, along with the shifting of Marcus inversion at lower exergonicity, the ET rates can also be maximized in a micellar media by using surfactant molecule as an intrinsic reactant.

Influence of confined water on the photophysics of dissolved solutes in reverse micelles.

The photophysical parameters of two probes with largely different hydrophobic character, namely, coumarin 1 and coumarin 343, are investigated in sodium bis-(2-ethylhexyl)sulfosuccinate (AOT)/hexane/water reverse micelles at various water/AOT molar ratio w(0). Correlation of photophysical parameters such as fluorescence quantum yield, fluorescence lifetime, and emission maxima with w(0) indicate distinctly different trends below and above w(0) approximately 7 for both probes. The variation of the average rotational correlation times obtained from fluorescence anisotropy decays for both probes in reverse micelles further corroborate the above observation. Similar studies were also performed in nonaqueous reverse micelles with acetonitrile as polar solvent. Similar to aqueous reverse micelles, breaks in the photophysical parameters with increasing acetonitrile/AOT molar ratios w'(0) were also observed in these cases, although at a much lower w'(0) value of 3. The present results indicate that around w(0) approximately 7 for aqueous reverse micelles (and around w'(0) approximately 3 for nonaqueous reverse micelles) a distinct change occurs in the probe microenvironment, which is rationalized on the basis of the relative populations of interfacial and core water. We propose that until the ionic head groups and counterions are fully solvated by polar solvents, that is, up to w(0) approximately 7 (or w'(0) approximately 3), the interfacial water population dominates. Above these molar ratios coalescence of excess water molecules with each other to form truncated H-bonded water clusters leads to a sizable population of core water. This is further substantiated by changes in the IR absorption spectra for the O--D stretching mode of diluted D(2)O in reverse micelles with varying w(0). Critical comparison of the present results with relevant literature reports provide clear support for the proposals made on water structure in reverse micelles. The role of relative size of the probe and the reverse micelles for differences in polar solvent to AOT ratios (w(0)=7 and w'(0)=3) in the observed breaks in the two types of reverse micelles is also discussed.

Photophysical properties of coumarin-7 dye: role of twisted intramolecular charge transfer state in high polarity protic solvents.

Photophysical studies on coumarin-7 (C7) dye in different protic solvents reveal interesting changes in the properties of the dye on increasing the solvent polarity (Deltaf; Lippert-Mataga solvent polarity parameter) beyond a critical value. Up to Deltaf approximately 0.31, the photophysical properties of the dye follow good linear correlations with Deltaf. For Deltaf > approximately 0.31, however, the photophysical properties, especially the fluorescence quantum yields (Phi(f)), fluorescence lifetimes (tau(f)) and nonradiative rate constants (k(nr)), undergo large deviations from the above linearity, suggesting an unusual enhancement in the nonradiative decay rate for the excited dye in these high polarity protic solvents. The effect of temperature on the tau(f) values of the dye has also been investigated to reveal the mechanistic details of the deexcitation mechanism for the excited dye. Studies have also been carried out in deuterated solvents to understand the role of solute-solvent hydrogen bonding interactions on the photophysical properties of the dye. Observed results suggest that the fluorescence of the dye originates from the planar intramolecular charge transfer (ICT) state in all the solvents studied and the deviations in the properties in high polarity solvents (Deltaf > approximately 0.31) arise due to the participation of a new deexcitation channel associated with the formation of a nonfluorescent twisted intramolecular charge transfer (TICT) state of the dye. Comparing present results with those of a homologous dye coumarin 30 (C30; Photochem. Photobiol., 2004, 80, 104), it is indicated that unlike in C30, the TICT state of the C7 dye does not experience any extra stability in protic solvents compared to that in aprotic solvents. This has been attributed to the presence of intramolecular hydrogen bonding between the NH group (in the 3-benzimidazole substituent) of the C7 dye and its carbonyl group, which renders an extra stability to the planar ICT state, making the TICT state formation relatively difficult. Qualitative potential energy diagrams have been proposed to rationalize the differences observed in the results with C7 and C30 dyes in high polarity protic solvents.