My Publications

Shape control is often necessary to tune the optical and electronic properties of nanocrystals (NCs) and is mostly achieved through manipulation of surface ligands and processing conditions. Here we present a versatile synthesis of colloidal CsPbBr3 perovskite NCs of various shapes (nanorods, nanocubes, and nanoplatelets) from an inexpensive steroidal Cs precursor: cesium cholate (CsCh). Cesium cholate has several advantages over the most commonly used Cs precursor (cesium oleate or Cs2CO3 or CsOAc) such as low cost, nonhygroscopicity, and better reproducibility in the perovskite synthesis. Due to the solubility of this Cs precursor in polar solvents such as methanol, a miniscule polar environment is created during the nucleation and growth of the nanocrystals leading to the serendipitous formation of nanorods at 180 °C, whereas using a biphasic mixture of 1-octadecene and methanol, the morphology changes to nanocubes. By lowering the reaction temperature (90 °C), nanoplatelets with 8–9 monolayers thicknesses are formed. These colloidal NCs of a variety of shapes are strongly luminescent with a green emission having narrow emission line widths (16–17 nm) and high quantum yields (96% for nanocubes, 94% for nanoplatelets). Furthermore, hybrid materials of nanocubes and organogel of a dimeric bile acid-derived ester gelator are obtained through coassembly in which nanocubes arrange along nanofibers with stable, sharp, and bright green emission. This enables spatial ordering of nanocubes ranging from micrometer to centimeter scale in thin films, which is crucial for advanced optoelectronic applications. To date, there is no report in the literature on the anisotropic organization of perovskite CsPbBr3 nanocubes triggered by supramolecular coassembly involving organogel nanofibers. Go To Article 

A variety of core‐shell CdSe‐CdS nanorods or quantum rods (QRs), both sphere (CdSe) in rod (CdS) and rod (CdSe) in rod (CdS) have been synthesized in a seeded‐growth approach using a very efficient and highly thermally stable steroidal cadmium precursor replacing the more common CdO: cadmium deoxycholate. The core‐shell QRs display high photoluminescence quantum yields (40–75%) and high molar absorption co‐efficient (ϵ=106 M−1 cm−1). Sphere‐in‐rods QRs can be co‐assembled with the organogelator diethylaminolithocholyl iodide in 1,2‐dichlorobenzene and with the hydrogelator calcium cholate in water to form hybrid gels. These organic‐inorganic hybrid soft materials are translucent and brightly red‐luminescent. The nanofibers composing the gel network act as a scaffold to support the dispersed QRs and impede their self‐aggregation. Furthermore, formation of original wire‐like assemblies of the nanorods is promoted in these gels, in particular in the hydrogel. This orientation occurs by a QR tip‐to‐tip interaction and is proposed to be driven by the amphiphilic behaviour of the QRs: laterally capped by negatively charged TGA (thioglycolic acid) ligands and un‐capped on the tips due to TGA unbinding. The combination of nanofiber‐forming hydrogelators and elongated quantum rods is promising in the perspective to form hybrid nanostructures with anisotropic optic or electronic properties. Go To Article 

Hybrid soft materials composed of CdSe–CdS nanorods or “quantum rods” (QRs) and the fluorescent 2,3‐didecyloxyanthracene (DDOA) low molecular weight organogelator are obtained through self‐assembly. Spectroscopy, microscopy, and rheology studies show that the QRs and DDOA coassemble, thereby stabilizing the organogels. Depending on the QR load and excitation wavelength, single nanofibers (NFs) of the hybrid gel display either sharp polarized red luminescence (under green excitation), or dual perpendicularly polarized blue and red emissions (under UV excitation). Transmission electron microscopy, microspectroscopy, and quantum rod orientation microscopy (QROM) reveal that QRs align along the organogel NFs with order parameters reaching 76% and 87%. This paves the way for obtaining surfaces of QR/NF assemblies yielding sharp red linearly polarized emission. In addition, this work demonstrates that QRs can be used more generally to probe nanostructured soft materials, even nonemissive ones. QROM allows to establish maps of the orientation of single QRs dispersed onto or within a gel network by measuring the polarization of the emission of the individual QRs. As occurs within this work in which QRs and NFs interact, the orientation of each QR reveals information on the underlying nanostructure (such as surface striation, bundle formation, and helicity). Go To Article 

We demonstrate in here a powerful scalable technology to synthesize continuously high quality CdSe quantum dots (QDs) in supercritical hexane. Using a low cost, highly thermally stable Cd-precursor, cadmium deoxycholate, the continuous synthesis is performed in 400 μm ID stainless steel capillaries resulting in CdSe QDs having sharp full-width-at-half-maxima (23 nm) and high photoluminescence quantum yields (45–55%). Transmission electron microscopy images show narrow particles sizes distribution (σ ≤ 5%) with well-defined crystal lattices. Using two different synthesis temperatures (250 °C and 310 °C), it was possible to obtain zinc blende and würtzite crystal structures of CdSe QDs, respectively. This synthetic approach allows achieving substantial production rates up to 200 mg of QDs per hour depending on the targeted size, and could be easily scaled to gram per hour. Go To Article

A new class of steroid dimers (bile acid derivatives) linked through ester functionalities were synthesized, which gelled various aromatic solvents. The organogels formed by the three dimeric ester molecules showed birefringent textures and fibrous nature by polarizing optical microscopy and scanning electron microscopy, respectively. A detailed rheological study was performed to estimate the mechanical strengths of two sets of organogels. In these systems, the storage modulus varied in the range of 0.8–3.5 × 104 at 1% w/v of the organogelators. The exponents of scaling of the storage modulus and yield stress of the two systems agreed well with those expected for viscoelastic soft colloidal gels with fibrillar flocs. The nanofibers in the organogel were utilized to engineer gold nanoparticles of different sizes and shapes and generate new gel–nanoparticle hybrid materials. Go To Article 

We have demonstrated that cadmium deoxycholate (1), a Cd-salt, provides a convenient and inexpensive route to high quality CdSe nanocrystals with photoluminescence (PL) in the blue to red region of the visible spectrum, with reproducible quantum yields as high as ∼47%. Owing to the high thermal stability of the bile acid based cadmium precursor (decomposition point: 332 °C), it was possible to achieve high injection and growth temperatures (∼300 °C) for the nanocrystals, which was essential for obtaining larger CdSe nanocrystals emitting in the red region (625–650 nm) with a sharp full width at half maximum (FWHM) (23 nm) and multiple (6–7) excitonic absorption features. The as-prepared CdSe nanocrystals synthesized from cadmium deoxycholate represent a series of highly efficient emitters with pure colours and controllable sizes, shapes and structures. Go To Article

This work describes the formation of hydrogels from sodium cholate solution in the presence of a variety of metal ions (Ca2+, Cu2+, Co2+, Zn2+, Cd2+, Hg2+ and Ag+). Morphological studies of the xerogels by electron microscopy reveal the presence of helical nanofibres. The rigid helical framework in the calcium cholate hydrogel was utilised to synthesize hybrid materials (AuNPs and AgNPs). Doping of transition metal salts into the calcium cholate hydrogel brings out the possibility of synthesising metal sulphide nano-architectures keeping the hydrogel network intact. These novel gel–nanoparticle hybrid materials have encouraging application potentials. Go To Article 

Two bile acid derived molecules containing basic amino groups are reported to be efficient and unusual gelators of organic and aqueous solvents. Go To Article