Sadananda Mandal

Surfactant-assisted porphyrin based hierarchical nano/micro assemblies and their efficient photocatalytic behavior.

In this report, we have demonstrated the synthesis of surfactant-assisted different morphologies of meso-tetra(4-carboxyphenyl)porphyrin assemblies (spherical to flower shaped). These nano/micro assemblies are well characterized by scanning electron microscopy and X-ray diffraction. The formation of assemblies is driven by noncovalent interactions such as hydrophobic-hydrophobic and aromatic π-π stacking between the molecules. The steady state and time-resolved spectroscopic investigation reveal that different assemblies are formed by virtue of special supramolecular organizations. The photocatalytic activities of different assemblies have been demonstrated with an organic pollutant Rhodamine B dye under the visible light irradiation. Such porphyrin based assemblies could pave the way for designing new optical based materials for the applications in photocatalytic, photovoltaic, and light harvesting system.

Photophysical properties of Au-CdTe hybrid nanostructures of varying sizes and shapes.

We design well-defined metal-semiconductor nanostructures using thiol-functionalized CdTe quantum dots (QDs)/quantum rods (QRs) with bovine serum albumin (BSA) protein-conjugated Au nanoparticles (NPs)/nanorods (NRs) in aqueous solution. The main focus of this article is to address the impacts of size and shape on the photophysical properties, including radiative and nonradiative decay processes and energy transfers, of Au-CdTe hybrid nanostructures. The red shifting of the plasmonic band and the strong photoluminescence (PL) quenching reveal a strong interaction between plasmons and excitons in these Au-CdTe hybrid nanostructures. The PL quenching of CdTe QDs varies from 40 to 86 % by changing the size and shape of the Au NPs. The radiative as well as the nonradiative decay rates of the CdTe QDs/QRs are found to be affected in the presence of both Au NPs and NRs. A significant change in the nonradiative decay rate from 4.72×10(6) to 3.92×10(10) s(-1) is obtained for Au NR-conjugated CdTe QDs. It is seen that the sizes and shapes of the Au NPs have a pronounced effect on the distance-dependent energy transfer. Such metal-semiconductor hybrid nanostructures should have great potentials for nonlinear optical properties, photovoltaic devices, and chemical sensors.

Photophysical and photoconductivity properties of thiol-functionalized graphene–CdSe QD composites

Graphene–semiconductor QD hybrid nanostructure materials have recently emerged as a new class of functional materials because of their potential applications in solar energy conversion, optoelectronic devices, sensing etc. Here, oleic acid-capped CdSe QDs are attached to –PhSH functionalized graphene by ligand exchange via bonding with the –SH group. The shifting of the G-band and D-band due to structural changes for the attachment of QD with graphene has been evaluated by using Raman spectroscopy. Steady state photoluminescence (PL) and time resolved fluorescence measurements have been employed to understand the electronic interactions between graphene and CdSe QDs. A time resolved fluorescence spectroscopic study has been used to understand the fluorescence dynamics of the photoexcitated CdSe QDs in the presence of graphene. It is evident that the electron transfer occurs from photoexcited QDs to graphene and the electron transfer rate is found to be 12.8 × 108 s−1 for 3.8 nm CdSe QDs. Photoconductivity properties of the graphene–QD device under illumination have been examined and it is to be noted that 2–3 fold increase in the photocurrent is found in this composite device in presence of 1.5 AM solar simulated light. The enhancement of the photocurrent in this hybrid device is found to be suitable for potential applications in optoelectronic and solar cell systems.

Photophysical properties of ionic liquid-assisted porphyrin nanoaggregate–nickel phthalocyanine conjugates and singlet oxygen generation

In this report, we demonstrate the formation of ionic liquid (IL)-assisted zinc octaethylporphyrin (ZnOEP) nanoaggregates which is confirmed by field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) studies. A large red shifted emission of ZnOEP nanoaggregates in comparison to ZnOEP in DCM confirmed the H aggregation which is due to intermolecular porphyrin–porphyrin (such as π–π/hydrophobic) interactions. The steady state and time resolved spectroscopic studies unambiguously confirm the H-aggregation formation of porphyrin molecules during nanoaggregate formation. The significant quenching of the fluorescence spectrum and the shortening of decay time of porphyrin nanoaggregates imply an efficient (89%) energy transfer from porphyrin nanoaggregates to phthalocyanine. Furthermore, the emission band observed at 1270 nm unambiguously confirms the singlet oxygen (1O2) generation from ZnOEP nanoaggregates which opens up further prospects in designing new IL-assisted porphyrin nanoaggregates for their application in photodynamic therapy.

Lanthanide based resonance energy transfer (LRET) between Ce-doped LaPO4 nanorods and coumarin 440 dye

Here, we demonstrate an efficient lanthanide based resonance energy transfer (LRET) between Ce-doped LaPO4 nanorods and coumarin 440 dye using steady state and time resolved spectroscopy. Water dispersible stable colloidal Ce-doped LaPO4 nanorods are synthesized via a facile aqueous route using a capping reagent 6-amino hexanoic acid (AHA). XRD and TEM analysis confirm the formation of uniform and discrete Ce-doped LaPO4 nanorods, having a tetragonal phase. FTIR analysis confirms that the surfaces of Ce-doped LaPO4 nanorods are functionalized with AHA. From zeta potential analysis, it is confirmed that the positively charged nanorods are attached to the negatively charged dye molecules electrostatically. Analysis suggests that both dynamic (1.04 × 104 M−1) and static quenching (3.3 × 102 M−1) processes occur in this assembled system. The prepared nanorods show an emission quantum yield of 10.2% and a long fluorescence lifetime (24.9 ns). The spectral overlap of the Ce3+ emission with the absorption of coumarin 440 dye molecules enables an efficient energy transfer from Ce-doped LaPO4 nanorods to coumarin 440 dye. The values of the overlap integral and Forster radius are found to be 2.028 × 1014 M−1 cm−1 nm4 and 27.02 A, respectively. The PL quenching and the shortening of the decay time of the donor (Ce-doped LaPO4 nanorods) confirm the energy transfer (24%) from the nanorods to the dye. Such energy transfer between LaPO4:Ce nanorods and C-440 dye could pave the way for designing new optical materials for potential applications.

Photon Harvesting in Sunscreen-Based Functional Nanoparticles.

The ultraviolet light component in the solar spectrum is known to cause several harmful effects, such as allergy, skin ageing, and skin cancer. Thus, current research attention has been paid to the design and fundamental understanding of sunscreen-based materials. One of the most abundantly used sunscreen molecules is Avobenzone (AB), which exhibits two tautomers. Here, we highlight the preparation of spherically shaped nanoparticles from the sunscreen molecule AB as well as from sunscreen-molecule-encapsulated polymer nanoparticles in aqueous media and study their fundamental photophysical properties by steady-state and time-resolved spectroscopy. Steady-state studies confirm that the AB molecule is in the keto and enol forms in tetrahydrofuran, whereas the enol form is stable in the case of both AB nanoparticles and AB-encapsulated poly(methyl methacrylate) (PMMA) nanoparticles. Thus, the keto-enol transformation of AB molecules is restricted to a nanoenvironment. An enhancement of photostability in both the nanoparticle and PMMA-encapsulated forms under UV light irradiation is observed. The efficient excited energy transfer (60 %) from AB to porphyrin molecules opens up further prospects in potential applications as light-harvesting systems.