Carbon-Dot Based Hybrid Nanomaterials: Synthesis and Spectroscopic Investigation

Recently, carbon dots have gained a prosperous interest due to their versatile applicability in the field of optoelectronics, biomedicine, sensing and catalysis. Low-toxicity, high photostability, high aqueous solubility of carbon dots make it a perfect alternative over traditional quantum dots. The origin of photoluminescence property is not clearly understood yet. It is believed that the conjugated core and the surface groups are responsible for the fluorescence property. These materials are promising for optoelectronic applications because of their electron accepting and donating properties. Therefore, we develop various synthesis methods for luminescent carbon dots and understand the origin and tuning of optical properties by using spectroscopy. Then, various carbon dots based hybrid nano-composites are designed to find out their potential applicability in energy transfer based light harvesting systems and photovoltaics.Research was conducted under supervision of Prof. Amitava PatraResearch was carried out under the CSIR fellowship and gran

Steady state and time resolved spectroscopic study of C-dots–MEH–PPV polymer nanoparticles composites

Fluorescent carbon dots (C-dots) have been found to be a new class of nanomaterial for potential applications. Herein, polyethylenimine branched (BPEI) functionalized carbon dots (C-dots) are synthesized by changing the synthesis time using a microwave pyrolysis method. The photoluminescence intensity and average decay time of C-dots are found to be increased with increasing the crystallinity of the C-dots. C-dots–MEH–PPV polymer nanoparticles composites are formed by electrostatic interaction between these particles. The intensity of C-dots quenches dramatically with increasing the concentration of MEH–PPV nanoparticles (PNPs) and the intensity of PNPs increases gradually under excitation at 370 nm. This phenomenon may be due to energy transfer from C-dots to PNPs because there is a good spectral overlap between the emission spectra of C-dots and the absorption spectra of PNPs. The drastic photoluminescence quenching and the shortening of the decay time of C-dots in the composites confirms the efficient resonance energy transfer from C-dots to polymer nanoparticles. The energy transfer efficiency (66% to 89%) and rate of energy transfer are found to depend strongly on the time of pyrolysis. These C-dots–polymer composites will open up a way for developing new challenging materials for potential applications

Photophysical properties of doped carbon dots (N, P, and B) and their influence on electron/hole transfer in carbon dots–nickel (II) phthalocyanine conjugates

Doping in carbon nanomaterial with various hetero atoms draws attention due to their tunable properties. Herein, we have synthesized nitrogen containing carbon dots [C-dots (N)], phosphorus co-doped nitrogen containing carbon dots [C-dots (N, P)], and boron co-doped nitrogen containing carbon dots [C-dots (N, B)]; and detailed elemental analysis has been unveiled by X-ray photoelectron spectroscopy (XPS) measurements. Our emphasis is given to understand the effect of doping on the photophysical behavior of carbon dots by using steady-state and time-resolved spectroscopy. Nitrogen containing carbon dots have quantum yield (QY) of 64.0% with an average decay time of 12.8 ns. Photophysical properties (radiative decay rate and average decay time) are found to be increased for phosphorus co-doping carbon dots due to extra electron incorporation for n-type doping (phosphorus dopant) to carbon dots which favors the radiative relaxation pathways. On the contrary, boron (p-type dopant) co-doping with nitrogen containing carbon dots favors the nonradiative electron–hole recombination pathways due to incorporation of excess hole; as a result QY, radiative rate, and average decay time are decreased. To understand the effect of doping on charge transfer phenomena, we have attached nickel (II) phthalocyanine on the surface of C-dots. It is seen that phosphorus co-doping carbon dots accelerates the electron transfer process from carbon dots to phthalocyanine. In contrast, after boron co-doping in carbon dots, the electron transfer process slows down and a simultaneous hole transfer process occurs

Light harvesting and white-light generation in a composite of carbon dots and dye-encapsulated BSA-protein-capped gold nanoclusters

Several strategies have been adopted to design an artificial light-harvesting system in which light energy is captured by peripheral chromophores and it is subsequently transferred to the core via energy transfer. A composite of carbon dots and dye-encapsulated BSA-protein-capped gold nanoclusters (AuNCs) has been developed for efficient light harvesting and white light generation. Carbon dots (C-dots) act as donor and AuNCs capped with BSA protein act as acceptor. Analysis reveals that energy transfer increases from 63 % to 83 % in presence of coumarin dye (C153), which enhances the cascade energy transfer from carbon dots to AuNCs. Bright white light emission with a quantum yield of 19 % under the 375 nm excitation wavelength is achieved by changing the ratio of components. Interesting findings reveal that the efficient energy transfer in carbon-dot–metal-cluster nanocomposites may open up new possibilities in designing artificial light harvesting systems for future applications

Photoswitching and thermoresponsive properties of conjugated multi-chromophore nanostructured materials

Conjugated multi-chromophore organic nanostructured materials have recently emerged as a new class of functional materials for developing efficient light-harvesting, photosensitization, photocatalysis, and sensor devices because of their unique photophysical and photochemical properties. Here, we demonstrate the formation of various nanostructures (fibers and flakes) related to the molecular arrangement (H-aggregation) of quaterthiophene (QTH) molecules and their influence on the photophysical properties. XRD studies confirm that the fiber structure consists of >95% crystalline material, whereas the flake structure is almost completely amorphous and the microstrain in flake-shaped QTH is significantly higher than that of QTH in solution. The influence of the aggregation of the QTH molecules on their photoswitching and thermoresponsive photoluminescence properties is revealed. Time-resolved anisotropic studies further unveil the relaxation dynamics and restricted chromophore properties of the self-assembled nano/microstructured morphologies. Further investigations should pave the way for the future development of organic electronics, photovoltaics, and light-harvesting systems based on π-conjugated multi-chromophore organic nanostructured materials

Photophysical Properties of Doped Carbon Dots (N, P, and B) and Their Influence on Electron/Hole Transfer in Carbon Dots–Nickel (II) Phthalocyanine Conjugates

Doping in carbon nanomaterial with various hetero atoms draws attention due to their tunable properties. Herein, we have synthesized nitrogen containing carbon dots [C-dots (N)], phosphorus co-doped nitrogen containing carbon dots [C-dots (N, P)], and boron co-doped nitrogen containing carbon dots [C-dots (N, B)]; and detailed elemental analysis has been unveiled by X-ray photoelectron spectroscopy (XPS) measurements. Our emphasis is given to understand the effect of doping on the photophysical behavior of carbon dots by using steady-state and time-resolved spectroscopy. Nitrogen containing carbon dots have quantum yield (QY) of 64.0% with an average decay time of 12.8 ns. Photophysical properties (radiative decay rate and average decay time) are found to be increased for phosphorus co-doping carbon dots due to extra electron incorporation for n-type doping (phosphorus dopant) to carbon dots which favors the radiative relaxation pathways. On the contrary, boron (p-type dopant) co-doping with nitrogen containing carbon dots favors the nonradiative electron–hole recombination pathways due to incorporation of excess hole; as a result QY, radiative rate, and average decay time are decreased. To understand the effect of doping on charge transfer phenomena, we have attached nickel (II) phthalocyanine on the surface of C-dots. It is seen that phosphorus co-doping carbon dots accelerates the electron transfer process from carbon dots to phthalocyanine. In contrast, after boron co-doping in carbon dots, the electron transfer process slows down and a simultaneous hole transfer process occurs

Singlet Oxygen Generation from Polymer Nanoparticles–Photosensitizer Conjugates Using FRET Cascade

Herein, we demonstrate π-conjugated polymer nanoparticles–photosensitizer conjugates for singlet oxygen generation via FRET cascade, which would be useful for photodynamic therapy. Rose Bengal (RB) molecules are attached on the surface of coumarin 153 (C153)-dye-doped poly­[<i>N</i>-vinyl carbazole] (PVK) polymer nanoparticles, where polymer nanoparticles act as efficient light-absorbing antenna materials. The energy funneling from C153 to RB at the excitation of the PVK host (340 nm) is confirmed by shortening of decay time of C153 and disappearing of its rise time. Again, it is evident that the efficient multistep energy transfer occurs from host PVK to RB dye molecules through C153 dye molecules to generate singlet oxygen (¹O₂) in solution. In addition, photo-oxidation of 2-chlorophenol provides quantitative evidence of singlet oxygen generation in different systems indirectly. The estimated singlet oxygen quantum yield for RB-attached C153-dye-doped PVK polymer nanoparticles is 21%. The present investigations should pave the way for future development of different photodynamic and theranostic devices