Femtosecond to nanosecond excited states dynamics of novel Corroles

We report a comprehensive photphysical investigation of some corrole molecules employing fs/nanosecond (ns) transient-absorption and time-resolved photoluminescence spectroscopy with support from the time-dependent density-functional theory calculations to understand their intramolecular charge transfer and polaron-absorption character

Metallated Macrocyclic Derivatives as a Hole - Transporting Materials for Perovskite Solar Cells

Spiro-OMeTAD is widely used as thehole-transporting material (HTM) in perovskite solar cells (PSC), which extracts positive charges and protects the perovskite materials from metal electrode, setting a new world-record efficiency of more than 20 %. Spiro-OMeTAD layer engross moisture leading to the degradation of perovskite, and therefore, has poor air stability. It is also expensive therefore limiting scale-up, so macrocyclic metal complex derivatives (MMDs) could be a suitable replacement. Our review covers low-cost, high yield hydrophobic materials with minimal steps required for synthesis of efficient HTMs for planar/mesostructured PSCs. The MMDs based devices demonstrated PCEs around 19 % and showed stability for a longer duration, indicating that MMDs are a promising alternative to spiro-OMeTAD and also easy to scale-up via solution approach. Additionally, this review describes how optical and electrical properties of MMDs change with chemical structure, allowing for the design of novel hole-mobility materials to achieve negligible hysteresis and act as effective functional barriers against moisture which results in a significant increase in the stability of the device. We provide an overview of the apt green-synthesis, characterization, stability and implementation of the various classes of macrocyclic metal complex derivatives as HTM for photovoltaic applications

Novel catalytic Hunsdiecker-Heck (CHH) strategy toward all-E stereocontrolled ferrocene-capped conjugated push-pull polyenes

Halodecarboxylation reaction of ferrocenylacrylic acid 1 and ferrocenyldienoic acid 3d with N-bromo- and N-iodosuccinimide in the presence of catalytic tetrabutylammonium trifluoroacetate at &#8722;40&#176;C and &#8722;78&#176;C affords the corresponding &#946;-halovinylferrocenes 2a, 2b and &#948;-haloferrocenyldiene 4 in 37-72% yields. Heck reaction of &#946;-iodovinylferrocene 2a with vinyl substrates (CH<SUB>2</SUB>=CH-Z where Z=CO<SUB>2</SUB>Me, CO<SUB>2</SUB>Et, COMe, CO<SUB>2</SUB>H, CONH<SUB>2</SUB>, 4'-NO<SUB>2</SUB>C<SUB>6</SUB>H<SUB>4</SUB>) in the presence of tri(4-tolyl)arsine/palladium acetate/lithium chloride/triethylamine in acetonitrile at 35-80&#176;C affords the corresponding ferrocenyldienes 3a-3f in 50-81% isolated yields. Similar reaction of &#948;-iodoferrocenyldiene 4 with vinyl substrates (CH<SUB>2</SUB>=CH-Z where Z=CO<SUB>2</SUB>Me, CO<SUB>2</SUB>Et, CO<SUB>2</SUB>H, 4'-NO<SUB>2</SUB>C<SUB>6</SUB>H<SUB>4</SUB>) affords the corresponding ferrocenyltrienes 5a-5d in 55-87% isolated yields. The ferrocene-capped conjugated dienes and trienes show excellent all-E stereoselectivity (vide NMR). The electronic, redox, and nonlinear optical properties of ferrocenylpolyenes have been evaluated. The data suggest that upon increasing the polyene chain length, (a) the absorption maxima shifts progressively to higher wavelength, (b) the oxidation potential of the Fc/Fc<SUP>+</SUP> couple (E<SUB>&#189;</SUB>) decreases, and (c) the HRS-derived second-order NLO response (&#946;) increases. From the insights derived from semiempirical calculation (ZINDO/1), a mechanism for the halodecarboxylation reaction has been proposed suggesting the prior formation of tetrabutylammonium salt of ferrocenylacrylic acid I. Attack of the halogenium atom at the &#960;<SUB>C=C</SUB> in I leads to the formation of intermediate II, and the latter triggers the elimination of carbon dioxide

Fluorescence and absorption spectroscopic studies on the interaction of porphyrins with snake gourd (Trichosanthes anguina) seed lectin

The interaction of several free-base porphyrins and their corresponding copper(II) and zinc(II) derivatives with the galactose-specific lectin from snake gourd (Trichosanthes anguina) seeds has been investigated by absorption and fluorescence spectroscopic techniques. The lectin dimer contains two apparently equivalent binding sites for the porphyrins. Association constants obtained for the interaction of various porphyrins with the lectin are in the range 1.7×104-6.2×105 M-1, with the metalloporphyrins being seen to have higher affinity for the lectin compared with the free-base analogues. Both positively charged and negatively charged porphyrins bind to snake gourd seed lectin (SGSL) with comparable affinities, suggesting that binding occurs primarily via hydrophobic interactions. Further, binding of porphyrins is found to be largely unaffected by the presence of the sugar ligand, lactose, indicating that the binding sites for the carbohydrate and porphyrin are different. This study thus suggests that the lectin may serve as a receptor for some endogenous non-carbohydrate, hydrophobic ligand in vivo, in addition to the saccharide ligands. It also opens up the possibility of employing the T. anguina lectin in applications such as photodynamic therapy, which involve the use of porphyrins

Ultrafast Interfacial Charge-Transfer Dynamics in a Donor-π-Acceptor Chromophore Sensitized TiO₂ Nanocomposite

The dynamics of interfacial charge transfer across (<i>E</i>)-3-(5-((4-(9H-carbazol-9-yl)­phenyl)­ethynyl)­thiophen-2-yl)-2-cyanoacrylic acid (CT-CA) and TiO₂ nanocomposites was studied with femtosecond transient absorption, fluorescence upconversion, and molecular quantum dynamics simulations. The investigated dye, CT-CA is a push–pull chromophore that has an intramolecular charge-transfer (ICT) excited state and binds strongly with the surface of TiO₂ nanoparticles. Ultrafast transient absorption and fluorescence measurements, in both solution and thin film samples, were carried out to probe the dynamics of electron injection and charge recombination. Multiexponential electron injection with time constants of <150 fs, 850 fs, and 8.5 ps were observed from femtosecond fluorescence measurements in solution and on thin films. Femtosecond transient absorption measurements show similar multiexponential electron injection and confirm that the picosecond electron injection component arises from the excited ICT state of the CT-CA/TiO₂ complex. Quantum dynamics calculations also show the presence of a slow component (30%) in the electron injection dynamics although most of the electron injection (70%) takes place in less than 20 fs. The slow component of electron injection, from the local ICT state, is attributed to the energetic position of the excited state, which is close to, or slightly below, the conduction band edge. In addition, the transient bleach of CT-CA on the TiO₂ surface is shifted to longer wavelengths when compared to its absorption spectrum and the transient bleach is further shifted to longer wavelengths with charge recombination. These features are attributed to transient Stark shifts that arise from the local electric fields generated at the dye/TiO₂ interface due to charge-transfer interactions