The photoexcited behavior of carbon nanoparticles (CNPs) and the effect of confinement on photoinduced electron transfer (PET) to and from the CNPs have been examined by confining the nanoparticles and electron donor−acceptor systems in aerosol OT (AOT)/hexane/water reverse micelles (RMs). The CNPs and the electron donor dimethylaniline (DMA) are captured in the nonpolar environment of the RMs, while methyl viologen (MV 2+ ), the electron acceptor, readily goes into the water pool. This confined medium facilitates experimentation on the electron transfer dynamics between two different phases. PET from DMA to MV 2+ via CNPs is the expected phenomenon. The ultrafast photogenerated MV •+ cation radical acts as an electron sink scavenging electrons from DMA. PET has been confirmed from steady-state and time-resolved fluorescence along with ultrafast transient absorption measurements. The kinetic details of PET in the DMA−CNP− MV 2+ assembly in a confined RM medium provide prospects toward development of light energy conversion devices. ■ INTRODUCTIONInterfacial electron transfer (IET) plays a key role in many applications, such as water purification, 1 solar energy conversion, 2 molecular electronics, 3 etc., and hence has attracted the attention of scientists. In ET phenomena, the injection and recombination rates depend on the strength of electronic coupling between light-harvesting molecules serving as the electron donor and a charge transport semiconductor acting as the electron acceptor. A popular example can be cited for application of photoinduced ET (PET) in semiconductor quantum dot (QD) solar cells where the QDs act as lightharvesting materials. 4−6 ET rates in donor−bridge−acceptor systems can be controlled by tuning the electronic coupling strength through the use of polymeric bridges between QDs and mesoporous oxides. 4 Boehme et al. studied PET between CdTe and CdSe QDs in a QD film. 5 They reported that efficient electron trapping in CdTe QDs obstructs electron transfer to CdSe QDs under most conditions. These examples show that QD−metal oxide junctions are integral parts of nextgeneration solar cells, light-emitting diodes, and nanostructured electronic arrays. Comprehensive examination of ET at metal oxide junctions by Tvrdy et al. using a series of CdSe QD donors and metal oxide nanoparticle acceptors shows that the ET rate constants depend strongly on the change in the system free energy. 6 With a similar purpose, Zhao et al. investigated the rate of PET from PbS@CdS core@shell QDs to wide band gap semiconducting mesoporous films. 7 They could fine-tune the electron injection rate by determining the width and height of the energy barrier for tunneling from the core to the oxide films using different electron affinities of the metal oxides, core sizes, and shell thicknesses. Although there have been a wide range of studies on this aspect, controversies often emerge regarding the quantum efficiency and the rate of charge transfer. 8 Harris et al. attempted to provide a better understanding of the eve...

Light-harvesting features of cyclometalated complexes of Ir(III) and Rh(III) contribute toward photoinduced electron and energy transfer for solar energy conversion and photocatalysis. Here we report four cyclometalated complexes of Rh and Ir among which one is heterometallic. These complexes, on interaction with fluorescent carbon nanoparticles (CNPs) in acetone medium, form molecular composites through hydrophobic interaction in the ground state followed by photoinduced electron transfer (PET). Quenching of CNP fluorescence and electrochemical measurements indicate occurrence of electron injection from the complexes to the CNPs.

Ligand-protected gold nanoclusters (Au NCs), generally being less fluorescent, are occasionally used as energy donors in Forster resonance energy-transfer (FRET) processes. Although several recent reports have stated methods to enhance the fluorescence quantum yield (QY) of Au NCs, these have limited applications. Ultrasmall Au NCs are reportedly nontoxic to biological cells limited to the protecting ligands. Herein, we have used a testified protocol to substantially enhance the fluorescence QY of the ligand-protected water-soluble Au NCs by rigidifying the protecting ligands using arginine, a physiologically essential amino acid. This has enabled us to use the Au NCs as energy donors to do FRET with a hemicyanine dye belonging to a family that is prospectively used in neuronal and mitochondrial centers in biological cells. We could hardly find applications of FRET to transfer photon energy to hemicyanine dyes using Au NCs or any metal NCs in the literature. This biofriendly FRET-based approach, creating an intrinsic antenna effect, could be useful in controlling the fluorescence emission from nanomaterials and conversion to energy useful for cellular functioning.

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Picric acid (PA) at low concentration is a serious water pollutant. Alongside, aliphatic amines (AAs) add to the queue to pollute surface water. Plenty of reports are available to sense PA with an ultralow limit of detection (LOD). However, only a handful of works are testified to detect AAs. A new fluorescent donor-acceptor compound has been synthesized with inherent intramolecular charge transfer (ICT) character that enables selective and sensitive colorimetric quantitative detection of PA and AAs with low LODs in nonaqueous as well as aqueous solutions. The synthesized compound is based on a hemicyanine skeleton containing two pyridenylmethylamino groups at the donor and a benzothiazole moiety at the acceptor ends. The detailed mechanisms and reaction dynamics are explained spectroscopically along with computational support. The fluorescence property of the detecting compound changes due to protonation of its pyridinyl centers by PA leading to quenching of fluorescence and subsequently de-protonation by AAs to revive the signal. We have further designed logic circuits from the acquired optical responses by sequential interactions.

The photophysical properties of a few Ir(III) and Rh(III) complexes have been attempted to be correlated (1–4) with their 1O2 generation efficiencies. A very weakly emissive pyrene‐functionalized Ir(III) complex (1) produces 1O2 more efficiently than the other more emissive Ir(III) complexes. All of them have excited triplet state lifetimes (τT) in the microsecond regime. However, the pyrene‐functionalized Ir(III) complex possesses the largest τT and has reasonable HOMO (highest occupied molecular orbital) energy (< –5.51 eV) which is desired for efficient 1O2 production. 1–4 emit mostly from the 3MLCT state. The lowest triplet emissive state of 3 and 4 is the 3MLCT state while it is the 3ILCT/3IL state for 1 which is mostly non‐emissive. However, the large excited state lifetime and the small energy gap between the 3ILCT/3IL states and the ground electronic state for complex 1 facilitates efficient energy transfer to molecular 3O2 producing 1O2.

In recent times, copper nanocluster (Cu NC) has become a promising candidate as an interesting nanomaterial for its potential applications in optoelectronics, sensing, catalysis and bioimaging. Herein, we have synthesized L–Cysteine protected Cu NC in 1:1 water:acetonitrile (ACN) solvent possessing bright cyan emission (λem=495 nm) with 10.4% quantum yield. Furthermore, the cyclometalated complexes of Ir(III) and Rh(III) are light harvesters, which are applied in photoinduced electron and energy transfer and photocatalysis. Three such cyclometalated complexes of Rh and Ir have been employed herein, which on electrostatic interaction with Cu NCs in 1:1 water:ACN medium, quench the fluorescence from Cu NC dramatically. This quenching could be suitably attributed to photoinduced electron transfer (PET) where Cu NC acts as an electron acceptor. PET has been confirmed by steady state and time resolved fluorescence spectroscopy as well as by ultrafast femtosecond upconversion and transient absorption spectroscopy.

The physicochemical behavior and characteristics of lipid vesicles and micelles in aqueous medium are greatly tuned by changing the ambient physical parameters, such as temperature, pH, and ionic strength. The process is also controlled by external additives and the nature of the surfactants. In this work, we have used water-soluble surfactant and cyclodextrin to transform lipid vesicles to micelles to vesicles without changing the physical ambience. In this regard, we have used a special pyrene-tagged guest compound that readily forms excimer in water and thus acts as a reporter for the process. Giant lipid vesicles (biological cell mimics) are disrupted by cationic surfactants to form mixed elongated micelles that transform to vesicles on applying a cyclodextrin host.