Investigation of the Effect of Substituents on Electronic and Charge Transport Properties of Benzothiazole Derivatives.

A series of new benzothiazole-derived donor-acceptor-based compounds (Comp1-4) were synthesized and characterized with the objective of tuning their multifunctional properties, i.e., charge transport, electronic, and optical. All the proposed structural formulations (Comp1-4) were commensurate using FTIR, 1H NMR, 13C NMR, ESI-mass, UV-vis, and elemental analysis techniques. The effects of the electron-donating group (-CH3) and electron-withdrawing group (-NO2) on the optoelectronic and charge transfer properties were studied. The substituent effect on absorption was calculated at the TD-B3LYP/6-31+G** level in the gas and solvent phases. The effect of solvent polarity on the absorption spectra using various polar and nonpolar solvents, i.e., ethanol, acetone, DMF, and DMSO was investigated. Light was shed on the charge transport in benzothiazole compounds by calculating electron affinity, ionization potential, and reorganization energies. Furthermore, the synthesized compounds were used to prepare thin films on the FTO substrate to evaluate the charge carrier mobility and other related device parameters with the help of I-V characteristic measurements.

An Li+-enriched Co2+-induced metallogel: a study on thixotropic rheological behaviour and conductance.

An alkali base and counterion-selective red metallogel (1% w/v) has been synthesized by mixing the adipic acid-derived ligand H2AL with LiOH, followed by the addition of 1 equivalent of Co(OAc)2 in DMF. The addition of Co(OAc)2 not only resulted in the formation of a 2 : 2 (M : L) complex, but also led to the consecutive steps of aggregation, fiber creation, entrapment of the solvent and eventually gelation. The metallogel formation and the mechanism behind gelation have been well characterized and established using various instrumental techniques such as FTIR spectroscopy, UV-vis spectroscopy, FE-SEM, TEM, PXRD, ESI-mass spectrometry, Job's plot and rheology analysis. Nyquist plots suggested a large decrease in the resistance value from 11.3 kΩ to 4.2 kΩ for the solution obtained from the ligand deprotonated by LiOH (AL2-) and Co(OAc)2 containing the metallogel. The Nyquist plot and resistance of the metallogel have also been studied under the influence of temperature and ultrasound stimuli. The extensive rheological measurements provide information about the strength of the gel network and the highly reversible nature and thixotropic behaviour of the metallogel.

Li+-Induced fluorescent metallogel: a case of ESIPT-CHEF and ICT phenomenon.

A fluorescent metallogel (1% w/v) has been synthesized from non-fluorescent ingredients viz. the smallest possible low molecular weight aromatic symmetrical ligand H2SA (1) and LiOH in a chloroform and methanol mixture. The chelation of Li+ is not only responsible for the inhibition of excited state intramolecular proton transfer (ESIPT) or the origin of fluorescence through chelation enhanced fluorescence (CHEF) in 1, but also for aggregation leading to gelation. The metallogel obtained from 1/Li+ reveals a fibrous morphology while 1 with other, bigger size, alkali metal ions like Na+/K+/Cs+ demonstrates the growth of crystals with different shapes. The effect of the size of the alkali metal ion over gel formation is well explored by FTIR, UV-vis, fluorescence, average lifetime measurements, SEM and PXRD. The metallogel shows multi-stimuli responsive behaviour towards thermal and mechanical stress as well as reswelling properties. The regioisomer H2PBA (2) also shows emission upon treatment with LiOH due to the presence of intramolecular charge transfer (ICT), this is well established by various experiments. The mechanism of gel formation is well established by FTIR, 1H NMR, UV-vis, fluorescence, lifetime measurements, SEM and single crystal and powder XRD instrumental techniques. The involvement of various phenomena in gel formation has been further supported by other synthesized model compounds viz. H2MBA (3), PMO (4), H2SEA (5) and H2SPA (6). True gel phase material is proved by detailed rheological experiments.

Alkali base triggered intramolecular charge transfer metallogels based on symmetrical A-π-D-chiral-D-π-A type ligands.

Three l-tartaric acid based symmetrical A-π-D-chiral-D-π-A type structural isomeric nitrobenzylidenes (1-3) have been synthesized with intent to achieve isomer specific metallogels with intramolecular charge transfer properties. Alkali metal ions in these systems not only trigger charge transfer but also play a vital role in gelation. The presence of intramolecular rather than intermolecular charge transfer as well as aggregation has been well established by various kinds of experiments using UV-vis, CD, (1)H NMR, DFT and crystallography techniques. The role of alkali metal ions in triggering ICT was proved by titration with their respective crown ethers. Notably, Na(+) afforded twisted fiber morphology whilst Li(+) gave merely long range fibers. The true gel phase material was proved by detailed rheological studies.

Anion triggered metallogels: demetalation and crystal growth inside the gel matrix and improvement in viscoelastic properties using Au-NPs.

Progelator complex Zn-TRPA-2 undergoes Cl(-) triggered gelation to afford ZTP2G, while Zn-TRPA-2 capped Au-NPs under similar conditions gave another gel GNZTP2G which also represents a rare nano-composite metallogel. When Zn-TRPA-2 was triggered by Cl(-) and NO3(-) simultaneously, crystals of demetalated species NA-TRPA-2 grew inside the ZTP2G matrix. Interestingly, GNZTP2G exhibits superior viscoelastic properties over ZTP2G.

Size-controlled synthesis of Ag nanoparticles functionalized by heteroleptic dipyrrinato complexes having meso-pyridyl substituents and their catalytic applications.

The syntheses of heteroleptic dipyrrinato nickel(II) complexes [Ni(4-pydpm)(dedtc)] (1) and [Ni(4-pydpm)(dipdtc)] (2) [4-pydpm = 5-(4-pyridyl)dipyrromethene; dedtc = diethyldithiocarabamate; and dipdtc = diisopropyldithiocarbamate] and the thorough characterization of these complexes by satisfactory elemental analyses, electrospray ionization mass spectrometry, Fourier-transform infrared, NMR ((1)H, (13)C), and UV-vis spectroscopies, and electrochemical studies was achieved. Structure of 1 was authenticated by X-ray single-crystal analysis. Both the complexes 1 and 2 were successfully utilized as a capping agent in the preparation of silver nanoparticles. Availability of free pyridyl nitrogen on the dipyrrin core of these complexes was meticulously exploited in functionalization and stabilization of the silver nanoparticles (AgNPs). Morphological and structural investigations on colloidal nanoparticles were followed by UV-vis spectroscopy and transmission electron microscopy (TEM). Overall results revealed that average size of the silver nanoparticles (∼10, 15, 20 nm, and aggregation) is strongly influenced by ratio of Ag/[1/2] (03, 06, 10, 20). Correlation between particle size and capping agents was realized by UV-vis and TEM studies. Catalytic activity of the AgNPs obtained through this route was successfully employed in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). It was established that reduction process follows a pseudo-first-order kinetics.

A Schiff base and its copper(II) complex as a highly selective chemodosimeter for mercury(II) involving preferential hydrolysis of aldimine over an ester group.

The syntheses of a new Schiff base, diethyl-5-(2-hydroxybenzylidene)aminoisophthalate (HL), and a copper complex, [Cu(L2)] (1), imparting L(-), have been described. Both the ligand HL and complex 1 have been thoroughly characterized by elemental analyses, electrospray ionization mass spectrometry, FT-IR, NMR ((1)H and (13)C), electronic absorption, and emission spectral studies and their structures determined by X-ray single-crystal analyses. Distinctive chemodosimetric behavior of HL and 1 toward Hg(2+) has been established by UV/vis, emission, and mass spectral studies. Comparative studies further revealed that the chemodosimetric response solely originates from selective hydrolysis of the aldimine moiety over the ester group and 1 exhibited greater selectivity toward Hg(2+) relative to HL while the sensitivity order is reversed. Further, these followed different hydrolytic pathways but ended up with the same product analyzed for diethyl-5-aminoisophthalate (DEA). Hg(2+)-induced displacement of Cu(2+) and subsequent hydrolysis of the -HC═N- moiety in 1 affirmed the identity of the actual species undergoing hydrolysis as HL. The occurrence of Cu(2+) displacement and Hg(2+) detection via hydrolytic transformation has been supported by various physicochemical studies.

Soft Ionic Diode Fabricated Using Asymmetric Ion Distribution in Li+-Zn(II)/Cu(II) Metallohydrogels.

The development of metal ions-incorporated soft materials is of great importance in the present scenario due to their essential requirement in the fabrication of the components such as ionic diodes and electrochemical transistors for soft electronic devices. In the current work, to fabricate a soft ionic diode, two distinct Li+-driven conductive metallohydrogels, namely, MG-Zn and MG-Cu, have been obtained by individually treating a LiOH deprotonated pregelator (H5APL) with Zn(OAc)2 or Cu(OAc)2. The pregelator and metallohydrogels have been well characterized by using various instrumental techniques, which supports their proposed formulations. Field emission scanning electron microscopic images of metallohydrogels reveal the presence of a fibrous network, which helps to create a gel matrix, whereas the rheological experimental results ascertain the true gel phase nature of the synthesized metallohydrogels. The obtained MG-Zn and MG-Cu metallohydrogels were subjected to electrochemical impedance spectroscopic and band gap measurements. The MG-Zn and MG-Cu showed ionic conductivities of 1.02 × 10-3 and 1.14 × 10-3 S/cm, along with band gaps of 2.82 and 2.85 eV, respectively, thus claiming their suitability for device fabrication. Further, the fabricated metallohydrogel-based ionic diode shows appreciable ability to rectify the ionic current with the forward and reverse bias currents of 19 and 1.9 mA at +/-4 V bias potential. Based on all the experimental results, the mechanism has been well established for the rectification behavior in the fabricated metallohydrogel ionic diode.

Green Synthesis of Pristine and Ag-Doped TiO2 and Investigation of Their Performance as Photoanodes in Dye-Sensitized Solar Cells.

Dye-sensitized solar cells (DSSCs) have emerged as a potential candidate for third-generation thin film solar energy conversion systems because of their outstanding optoelectronic properties, cost-effectiveness, environmental friendliness, and easy manufacturing process. The electron transport layer is one of the most essential components in DSSCs since it plays a crucial role in the device's greatest performance. Silver ions as a dopant have drawn attention in DSSC device applications because of their stability under ambient conditions, decreased charge recombination, increased efficient charge transfer, and optical, structural, and electrochemical properties. Because of these concepts, herein, we report the synthesis of pristine TiO2 using a novel green modified solvothermal simplistic method. Additionally, the prepared semiconductor nanomaterials, Ag-doped TiO2 with percentages of 1, 2, 3, and 4%, were used as photoanodes to enhance the device's performance. The obtained nanomaterials were characterized using XRD, FTIR, FE-SEM, EDS, and UV-vis techniques. The average crystallite size for pristine TiO2 and Ag-doped TiO2 with percentages of 1, 2, 3, and 4% was found to be 13 nm by using the highest intensity peaks in the XRD spectra. The Ag-doped TiO2 nanomaterials exhibited excellent photovoltaic activity as compared to pristine TiO2. The incorporation of Ag could assist in successful charge transport and minimize the charge recombination process. The DSSCs showed a Jsc of 8.336 mA/cm2, a Voc of 698 mV, and an FF of 0.422 with a power conversion efficiency (PCE) of 2.45% at a Ag concentration of 4% under illumination of 100 mW/cm2 power with N719 dye, indicating an important improvement when compared to 2% Ag-doped (PCE of 0.97%) and pristine TiO2 (PCE of 0.62%).

A Li+-integrated metallohydrogel-based mixed conductive electrochemical semiconductor.

A metallohydrogel (STG)-based mixed conductive electrochemical semiconductor has been obtained via LiOH-deprotonation of a pre-gelator (H4STL) followed by treatment with Cd(OAc)2. The gelation mechanism of STG, its mixed ionic-electronic conductive nature and application towards an electrochemical semiconductor were well explored by using various techniques including EIS studies.

Cd2+ -induced Fluorescent Metallogel: A Case of CHEF and ACQ Phenomena.

A fluorescent metallogel (1 %w/v) has been synthesized from deprotonation of a non-fluorescent adipic acid-derived ligand H2 AL with LiOH followed by coordination with Cd2+ in DMF. Cd2+ not only induces the coordination complex formation but also leads to aggregation, formation of nanofibers of about ≈12 nm average diameter and gelation. The metallogel was also found to be reversibly stimuli-responsive towards heating and mechanical shaking whereas it was resistant to ultrasound. The involvement of chelation-enhanced fluorescence (CHEF), aggregation-induced emission (AIE) and aggregation-caused quenching (ACQ) during the course of gelation has been well established by fluorescence experiments. Further, the coordination complex involved in metallogel formation has been well characterized by ESI-MS and Job's plot. The synthesized metallogel has a true gel phase as shown by detailed rheological studies. The mechanism of gelation is well established by using FTIR, UV-vis, fluorescence, lifetime measurement, Job's plot, ESI-MS, PXRD and TEM techniques.

Investigation of the Mechanism Behind Conductive Fluorescent and Multistimuli-responsive Li+ -enriched Metallogel Formation.

A fluorescent metallogel (2.6 % w/v) has been obtained from two non-fluorescent components viz. phenyl-succinic acid derived pro-ligand H2 PSL and LiOH (2 equiv.) in DMF. Li+ ion not only plays a crucial role in gelation through aggregation, but also contributed towards enhancement of fluorescence by imposing restriction over excited state intramolecular proton transfer (ESIPT) followed by origin of chelation enhanced fluorescence (CHEF) phenomenon. Further, the participation of CHEF followed by aggregation-caused quenching (ACQ) and aggregation-induced emission (AIE) in the gelation process have been well established by fluorescence experiments. Transmission electron microscopy (TEM) analysis disclosed the sequential creation of nanonuclei followed by nanoballs and their alignment towards the generation of fibers of about 3, 31 and 40 nm diameter, respectively. The presence of a long-range fibrous morphology inside the metallogel was further attested by scanning electron microscopy (SEM). Rheological studies on the metallogel showed its true gel-phase material nature. Nyquist impedance study shows a resistance value of 7.4 kΩ for the metallogel which upon applying ultrasound increased to 8.5 kΩ, while an elevated temperature of 70 °C caused reduction in the resistance value to 4.8 kΩ. The mechanism behind metallogel formation has been well established by using FTIR, UV-vis, SEM, TEM, PXRD, 1 H NMR, fluorescence and ESI-MS.

Sodium and potassium ion directed self-assembled multinuclear assembly of divalent nickel or copper and L-leucine derived ligand.

L-leucine derived ligand (H(2)L(L-leu)), KOH, and Ni(II) salt in 2:2:1 ratio self-assembled into a rather large (approximately 13 A) supramolecular assembly with the formula [K{Ni(HL(L-leu))(2)}(3)](+) (1). Structural characterization showed three [Ni(HL(L-leu))(2)] units encapsulated K(+) similar to organic crown ethers/cryptand. Substituting Ni(II) with Cu(II) and K(+) with Na(+) in the above reaction resulted in a set of structurally identical assemblies with the general formula [M'{M(HL(L-leu))(2)}(3)](+), where M' is either K(+) or Na(+) and M is either Cu(II) or Ni(II); [Na{Ni(HL(L-leu))(2)}(3)]ClO(4) (2), Na{Ni(HL(L-leu))(2)}(3)]OTf (3), [K{Cu(HL(L-leu))(2)}(3)]ClO(4) (4), [Na{Cu(HL(L-leu))(2)}(3)]ClO(4) (5), [K{Cu(HL(L-leu))(2)}(3)]NO(3) (6). Electrospray Ionization (ESI)-mass spectra of the assemblies in MeOH showed the retention of assemblies in solution. Visible spectroscopic studies showed retention of assembly 1 in N,N-dimethylformamide (DMF) which is stable even after the addition of 5 equiv of [18]-crown-6. The assemblies in 2-6 show various degrees of dissociation to [M(HL(L-leu))(2)] and M', in stronger H-bonding methanol. The dissociation can be reversed upon addition of excess KNO(3)/NaNO(3) salt. Structural characterization of [Cu(HL(L-leu))(2)(MeCN)] (7) along with its transformation to [K{Cu(HL(L-leu))(2)}(3)](+) in the presence of K(+) salt demonstrated that the assembly formation proceeds through an alkali metal ion induced ligand reorientation within the [Cu(HL(L-leu))(2)] units which is further stabilized by six strong H-bonds holding the assembly. Interestingly, visible spectra of 1 and 2 shows that minor structural changes caused by replacing K(+) with Na(+) is sufficient to shift the d-d transition of Ni(II) by approximately 70 nm, thereby providing an indirect way of distinguishing K(+) and Na(+), none of which have spectroscopic signature in the visible range.

Self-assembled copper(II) metallacycles derived from asymmetric Schiff base ligands: efficient hosts for ADP/ATP in phosphate buffer.

Novel asymmetric Schiff base ligands 2-{[3-(3-hydroxy-1-methyl-but-2-enylideneamino)-2,4,6-trimethylphenylimino]-methyl}-phenol (H2L(1)) and 1-{[3-(3-hydroxy-1-methyl-but-2-enylideneamino)-2,4,6-trimethylphenylimino]-methyl}-naphthalen-2-ol (H2L(2)) possessing dissimilar N,O-chelating sites and copper(ii) metallacycles (CuL(1))4 (1) and (CuL(2))4 (2) based on these ligands have been described. The ligands and complexes have been thoroughly characterized by satisfactory elemental analyses, and spectral (IR, (1)H, (13)C NMR, ESI-MS, UV/vis) and electrochemical studies. Structures of H2L(2) and 1 have been unambiguously determined by X-ray single crystal analyses. The crystal structure of H2L(2) revealed the presence of two distinct N,O-chelating sites on dissimilar cores (naphthalene and ß-ketoaminato groups) offering a diverse coordination environment. Metallacycles 1 and 2 having a cavity created by four Cu(ii) centres coordinated in a homo- and heteroleptic fashion with respective ligands act as efficient hosts for adenosine-5'-diphosphate (ADP) and adenosine-5'-triphosphate (ATP) respectively, over other nucleoside polyphosphates (NPPs). The disparate sensitivity of these metallacycles toward ADP and ATP has been attributed to the size of the ligands assuming diverse dimensions and spatial orientations. These are attuned for π-π stacking and electrostatic interactions suitable for different guest molecules under analogous conditions, metallacycle 1 offers better orientation for ADP, while 2 for ATP. The mechanism of the host-guest interaction has been investigated by spectral and electrochemical studies and supported by molecular docking studies.

Morphological tuning via structural modulations in AIE luminogens with the minimum number of possible variables and their use in live cell imaging.

With intent to fine tune the morphological and photophysical properties, three novel AIE luminogens (BQ1-BQ3) based on quinoline-BODIPY have been synthesized. A judicious choice of substituents (-H, -CH3, -OCH3) in these systems led to nanoballs in BQ1 and BQ2, while in BQ3 it led to reticulated nanofibers with diverse photophysical behaviours.

A dual-responsive "turn-on" bifunctional receptor: a chemosensor for Fe3+ and chemodosimeter for Hg2+.

Synthesis of L1-L3, their thorough characterization by spectral as well as structural studies and use in selective photochemical detection of Fe(3+) and Hg(2+) at ppb level have been described. Notably, these exhibit bifunctional behaviour toward Fe(3+) (CHEF) and Hg(2+) (chemodosimetric) which has been unequivocally established by various studies.

Homochiral coordination polymeric gel: Zn(2+)-induced conformational changes leading to J-aggregated helical fibres formation.

A novel chiral coordination polymeric gel based on an amino acid derived symmetrical ligand, specific base, and Zn(2+) has been described. Zn(2+) induced conformational reorganization in the ligand leads to gelation via J-aggregated helical fibres. The vital role played by π-π stacking in gelation has been monitored by fluorescence and NMR spectroscopy.

A saponification-triggered gelation of ester-based Zn(II) complex through conformational transformations.

Novel saponification-triggered gelation in an ester-based bis-salen Zn(II) complex (1) is described. Strategic structural modifications induced by NaOH in 1 tune the dipolar-/π-interactions leading to J-aggregation and the creation of an inorganic gel material (IGM), which has been established by photophysical, DFT and rheological studies.

Li(+)-induced selective gelation of discrete homochiral structural isomers derived from L-tartaric acid.

Two chiral structural isomers have been synthesized by molecular engineering of L-tartaric acid. In the presence of LiOH isomer forms a thermally stable, fluorescent gel which exhibits interesting nano-cluster morphology, anomalous optical and rheological properties whilst forms a non-fluorescent solution under similar conditions. The current-voltage (I-V) curve followed a non-linear trend, rationally in close proximity to the diode characteristic curve.

Novel tetranuclear copper |2 + 4| cubanes resulting from unprecedented C-O bond formation cum dearomatization.

Novel tetranuclear copper |2 + 4| cubanes 1 and 2 have been synthesized from the reaction of hydrated copper salts/precursors with N,O chelating ß-ketoaminato ligands. Creation of 1 and 2 occurs by in situ generation of the tridentate chelating species HL1O(2-) via copper mediated C-O bond formation and dearomatization of H3L1, while anhydrous salts afforded mononuclear complex 3.