We investigated the charge transfer interactions between luminescent quantum dots (QDs) and redox active dopamine. For this, we used pH-insensitive ZnS-overcoated CdSe QDs rendered water-compatible using poly (ethylene glycol)-appended dihydrolipoic acid (DHLA-PEG), where a fraction of the ligands was amine-terminated to allow for controlled coupling of dopamine-isothiocyanate onto the nanocrystal. Using this sample configuration, we probed the effects of changing the density of dopamine and the buffer pH on the fluorescence properties of these conjugates. Using steady-state and time-resolved fluorescence, we measured a pronounced pH-dependent photoluminescence (PL) quenching for all QD-dopamine assemblies. Several parameters affect the PL loss. First, the quenching efficiency strongly depends on the number of dopamines per QD-conjugate. Second, the quenching efficiency is substantially increased in alkaline buffers. Third, this pH-dependent PL loss can be completely eliminated when oxygen-depleted buffers are used, indicating that oxygen plays a crucial role in the redox activity of dopamine. We attribute these findings to charge transfer interactions between QDs and mainly two forms of dopamine: the reduced catechol and oxidized quinone. As the pH of the dispersions is changed from acidic to basic, oxygen-catalyzed transformation progressively reduces the dopamine potential for oxidation and shifts the equilibrium toward increased concentration of quinones. Thus, in a conjugate, a QD can simultaneously interact with quinones (electron acceptors) and catechols (electron donors), producing pH-dependent PL quenching combined with shortening of the exciton lifetime. This also alters the recombination kinetics of the electron and hole of photoexcited QDs. Transient absorption measurements that probed intraband transitions supported those findings where a simultaneous pronounced change in the electron and hole relaxation rates was measured when the pH was changed from acidic to alkaline.

We report a new strategy for the photomediated phase transfer of luminescent quantum dots, QDs, and potentially other inorganic nanocrystals, from hydrophobic to polar and hydrophilic media. In particular, we demonstrate that UV-irradiation (λ < 400 nm) promotes the in situ ligand exchange on hydrophobic CdSe QDs with lipoic acid (LA)-based ligands and their facile QD transfer to polar solvents and to buffer media. This convenient method obviates the need to use highly reactive agents for chemical reduction of the dithiolane groups on the ligands. It maintains the optical and spectroscopic properties of the QDs, while providing high photoluminescence yield and robust colloidal stability in various biologically relevant conditions. Furthermore, development of this technique significantly simplifies the preparation and purification of QDs with sensitive functionalities. Application of these QDs to imaging the brain of live mice provides detailed information about the brain vasculature over the period of a few hours. This straightforward approach offers exciting possibilities for expanded functional compatibilities and reaction orthogonality on the surface of inorganic nanocrystals.

We describe the colloidal hot-injection synthesis of phase-pure nanocrystals (NCs) of a highly abundant mineral, chalcopyrite (CuFeS2). Absorption bands centered at around 480 and 950 nm, spanning almost the entire visible and near-infrared regions, encompass their optical extinction characteristics. These peaks are ascribable to electronic transitions from the valence band (VB) to the empty intermediate band (IB), located in the fundamental gap and mainly composed of Fe 3d orbitals. Laser-irradiation (at 808 nm) of an aqueous suspension of CuFeS2 NCs exhibited significant heating, with a photothermal conversion efficiency of 49%. Such efficient heating is ascribable to the carrier relaxation within the broad IB band (owing to the indirect VB–IB gap), as corroborated by transient absorption measurements. The intense absorption and high photothermal transduction efficiency (PTE) of these NCs in the so-called biological window (650–900 nm) make them suitable for photothermal therapy as demonstrated by tumor cell annihilation upon laser irradiation. The otherwise harmless nature of these NCs in dark conditions was confirmed by in vitro toxicity tests on two different cell lines. The presence of the deep Fe levels constituting the IB is the origin of such enhanced PTE, which can be used to design other high performing NC photothermal agents.

Mechanically interlocked molecules [1] (MIMs) in the form of multi-and bistable rotaxanes in which the ring component can be switched between different co-conformations in response to external stimuli, constitute an artificial molecular switch. [2] They are of importance when it comes to the development of integrated systems and devices, [3] such as responsive surfaces, [4] molecule-based muscles and actuators, [1d, 5] nanovalves for controlled drug delivery, [6] and molecular electronic devices [7] (MEDs). Although the operation of bistable molecular switches is based on classical switching processes between thermodynamically stable states, it has become clear that the fulfillment of useful functions will only become possible if the rates of the mechanical movement between such states can also be controlled. This approach was used [8] recently to implement ratchet-type mechanisms [9] which are essential ingredients for the construction of molecular motors, [10] and is of considerable relevance for the development of sequential logic devices such as flip-flops and memories.[11] For all these purposes, the ability to be able to adjust the shuttling kinetics [12] by modulating the corresponding energy barriers through external stimuli in a convenient, efficient, and reversible manner [13] is a goal which still poses a considerable challenge to chemists.Herein, we discuss the performance of a molecular switch in the form of a bistable [2]rotaxane (Scheme 1), which 1) undergoes relative mechanical movements of its ring and dumbbell components under redox control and thus can be switched between two states thermodynamically, and wherein 2) the energy barriers between these two states can be controlled kinetically by photochemical means.The design of [2]rotaxane 1 4+ (Scheme 1) is based on a well-studied architecture [7b, 14] in which the ring component is cyclobis(paraquat-p-phenylene) (CBPQT 4+ ) and the dumbbell component is comprised of 1) a tetrathiafulvalene (TTF) Scheme 1. Synthesis of [2]rotaxane trans-1·4 PF 6 and the corresponding dumbbell trans-2.

We report a simple method for the incorporation of Cu(I) or (64)Cu(I) radionuclides in covellite nanocrystals (CuS NCs). After the in situ reduction of Cu(II) or (64)Cu(II) ions by ascorbic acid, their incorporation in PEG-coated CuS NCs takes place at room temperature. In all the reaction steps, the stability of the NCs under physiological conditions was ensured. The copper incorporation reaction could also take place on CuS NCs bearing biotin molecules at their surface, with no detrimental effects on the specific binding affinity of the NCs toward streptavidin after incorporation. At low loading of Cu ions, the strong near-infrared (NIR) absorption band of the starting CuS NCs was essentially preserved, which allowed for efficient plasmonic photothermal therapy. The combined presence in the NCs of (64)Cu ions, well suitable for positron emission tomography, and of free carriers responsible for the NIR absorption, should enable their theranostic use as radiotracers and as photothermal probes in tumor ablation treatments. Moreover, the simplicity of the preparation scheme, which involves the use of radioactive species only as a last step, makes the protocol easily transferable to the clinical practice.