Femtosecond Time-Resolved Transient Absorption Spectroscopy of CH₃NH₃PbI₃ Perovskite Films: Evidence for Passivation Effect of PbI₂

CH₃NH₃PbI₃ perovskite layered films deposited on substrates with and without a titania support structure have been prepared and studied using time-resolved femtosecond transient absorption (fs-TA) spectroscopy in the visible light range (450–800 nm). The electron injection dynamics from the photoexcited perovskite layers to the neighboring film structures could be directly monitored via the transient bleaching dynamics of the perovskite at ∼750 nm and thus systematically studied as a function of the layer-by-layer architecture. In addition, for the first time we could spectrally distinguish transient bleaching at ∼750 nm from laser-induced fluorescence that occurs red-shifted at ∼780 nm. We show that an additional bleach feature at ∼510 nm appears when PbI₂ is present in the perovskite film. The amplitudes of the PbI₂ and perovskite TA peaks were compared to estimate relative amounts of PbI₂ in the samples. Kinetic analysis reveals that perovskite films with less PbI₂ show faster relaxation rates than those containing more PbI₂. These fast dynamics are attributed to charge carrier trapping at perovskite grain boundaries, and the slower dynamics in samples containing PbI₂ are due to a passivation effect, in line with other recently reported work

Near-Infrared Emitting AgInS₂/ZnS Nanocrystals

Near-infrared emitting AgInS₂/ZnS nanocrystals were synthesized by carefully controlling the growth conditions in a Ag/In/Zn/S solution with less zinc relative to the other precursors. The role of having a smaller amount of zinc (8 atom %) was systematically investigated in an effort to understand the mechanism of the largely red-shifted emission. The AgInS₂/ZnS nanocrystals can be transferred to aqueous solutions while retaining the emission intensity. The near-infrared emission and solubility in aqueous solutions make AgInS₂/ZnS nanocrystals excellent candidates for bioimaging and photocatalytic applications

Designing CdS-Based Ternary Heterostructures Consisting of Co-Metal and CoO_<i>x</i> Cocatalysts for Photocatalytic H₂ Evolution under Visible Light

Heterostructure formation is an effective method used for designing photocatalysts that solve problems caused by photoexcited charge recombination phenomena associated with the photocatalytic water redox reaction. This work reports a new Co-metal-incorporated ternary heterostructured photocatalyst, CdS/CoOx/Co-metal, which enhanced charge separation to increase photocatalytic H2 evolution 30.5-fold in comparison to pure CdS under visible light. This work demonstrates for the first time the effect of the Co metal on photocatalytic H2 evolution using the CdS/CoOx/Co-metal ternary heterostructure. In the ternary heterostructure, Co metal and CoOx act as photogenerated electron- and hole-capturing cocatalysts, respectively. Results from photoelectrochemical studies along with photocatalytic H2 evolution data proved the enhancement of charge transfer and separation in the CdS/CoOx/Co-metal heterostructure due to the addition of Co metal and CoOx. Hence, the synergistic charge separation improvement achieved by the combination of CoOx and the Co metal with CdS produced a photocatalytic H2 evolution rate of 9.54 μmol/h, which is the highest reported H2 evolution rate for a CdS-based system under l sun solar irradiance (>420 nm) to the best of our knowledge

Synthesis and Photoelectrochemical Properties of (Cu₂Sn)_<i>x</i>Zn_{3(1–<i>x</i>)}S₃ Nanocrystal Films

This work provides new routes for developing efficient photoelectrodes for photoelectrochemical (PEC) water splitting using a low-cost electrophoretic film preparation method. A series of (Cu₂Sn)_<i>x</i>Zn_{3(1–<i>x</i>)}S₃ (0 ≤ <i>x</i> ≤ 0.75) quaternary nanocrystals (NCs) with tunable optical band gaps are synthesized. Morphologies including particles, rods, and wires are obtained by tuning the composition of the NCs. (Cu₂Sn)_0.75Zn_0.75S₃ (Cu₂ZnSnS₄) has a pure kesterite structure, but an increase in the Zn content results in a kesterite–wurtzite polytypism. (Cu₂Sn)_<i>x</i>Zn_{3(1–<i>x</i>)}S₃ films are fabricated from their colloidal solutions via electrophoretic deposition, and the PEC properties of these films with p-type character have been examined under water-splitting conditions. It is shown that the photocurrent varies as a function of film thickness as well as chemical composition. The produced (Cu₂Sn)_0.45Zn_1.65S₃ (<i>x</i> = 0.45) film has the highest photocurrent, and the incident photon to current conversion efficiency is improved compared with previously reported results of Cu₂ZnSnS₄ photocathodes

Photoinduced Homolytic Bond Cleavage of the Central Si–C Bond in Porphyrin Macrocycles Is a Charge Polarization Driven Process

Photoinduced cleavage of the bond between the central Si atom in porphyrin macrocycles and the neighboring carbon atom of an axial alkyl ligand is investigated by both experimental and computational tools. Photolysis and electron paramagnetic resonance measurements indicate that the Si–C bond cleavage of Si–phthalocyanine occurs through a homolytic process. The homolytic process follows a low-lying electronic excitation of about 1.8 eV that destabilizes the carbide bond of similar bond dissociation energy. Using electronic structure calculations, we provide insight into the nature of the excited state and the resulting photocleavage mechanism. We explain this process by finding that the electronic excited state is of a charge transfer character from the axial ligand toward the macrocycle in the reverse direction of the ground state polarization. We find that the homolytic process yielding the radical intermediate is energetically the most stable mechanistic route. Furthermore, we demonstrate using our computational approach that changing the phthalocyanine to smaller ring system enhances the homolytic photocleavage of the Si–C bond by reducing the energetic barrier in the relevant excited states

Prostate-Specific Membrane Antigen Targeted Gold Nanoparticles for Theranostics of Prostate Cancer

Prostate cancer is one of the most common cancers and among the leading causes of cancer deaths in the United States. Men diagnosed with the disease typically undergo radical prostatectomy, which often results in incontinence and impotence. Recurrence of the disease is often experienced by most patients with incomplete prostatectomy during surgery. Hence, the development of a technique that will enable surgeons to achieve a more precise prostatectomy remains an open challenge. In this contribution, we report a theranostic agent (AuNP-5kPEG-PSMA-1-Pc4) based on prostate-specific membrane antigen (PSMA-1)-targeted gold nanoparticles (AuNPs) loaded with a fluorescent photodynamic therapy (PDT) drug, Pc4. The fabricated nanoparticles are well-characterized by spectroscopic and imaging techniques and are found to be stable over a wide range of solvents, buffers, and media. <i>In vitro</i> cellular uptake experiments demonstrated significantly higher nanoparticle uptake in PSMA-positive PC3pip cells than in PSMA-negative PC3flu cells. Further, more complete cell killing was observed in Pc3pip than in PC3flu cells upon exposure to light at different doses, demonstrating active targeting followed by Pc4 delivery. Likewise, <i>in vivo</i> studies showed remission on PSMA-expressing tumors 14 days post-PDT. Atomic absorption spectroscopy revealed that targeted AuNPs accumulate 4-fold higher in PC3pip than in PC3flu tumors. The nanoparticle system described herein is envisioned to provide surgical guidance for prostate tumor resection and therapeutic intervention when surgery is insufficient

Prostate-Specific Membrane Antigen Targeted Gold Nanoparticles for Theranostics of Prostate Cancer

Prostate cancer is one of the most common cancers and among the leading causes of cancer deaths in the United States. Men diagnosed with the disease typically undergo radical prostatectomy, which often results in incontinence and impotence. Recurrence of the disease is often experienced by most patients with incomplete prostatectomy during surgery. Hence, the development of a technique that will enable surgeons to achieve a more precise prostatectomy remains an open challenge. In this contribution, we report a theranostic agent (AuNP-5kPEG-PSMA-1-Pc4) based on prostate-specific membrane antigen (PSMA-1)-targeted gold nanoparticles (AuNPs) loaded with a fluorescent photodynamic therapy (PDT) drug, Pc4. The fabricated nanoparticles are well-characterized by spectroscopic and imaging techniques and are found to be stable over a wide range of solvents, buffers, and media. <i>In vitro</i> cellular uptake experiments demonstrated significantly higher nanoparticle uptake in PSMA-positive PC3pip cells than in PSMA-negative PC3flu cells. Further, more complete cell killing was observed in Pc3pip than in PC3flu cells upon exposure to light at different doses, demonstrating active targeting followed by Pc4 delivery. Likewise, <i>in vivo</i> studies showed remission on PSMA-expressing tumors 14 days post-PDT. Atomic absorption spectroscopy revealed that targeted AuNPs accumulate 4-fold higher in PC3pip than in PC3flu tumors. The nanoparticle system described herein is envisioned to provide surgical guidance for prostate tumor resection and therapeutic intervention when surgery is insufficient

Excitonic Interactions in Bacteriochlorin Homo-Dyads Enable Charge Transfer: A New Approach to the Artificial Photosynthetic Special Pair

Excitonically coupled bacteriochlorin (BC) dimers constitute a primary electron donor (special pair) in bacterial photosynthesis and absorbing units in light-harvesting antenna. However, the exact nature of the excited state of these dyads is still not fully understood. Here, we report a detailed spectroscopic and computational investigation of a series of symmetrical bacteriochlorin dimers, where the bacteriochlorins are connected either directly or by a phenylene bridge of variable length. The excited state of these dyads is quenched in high-dielectric solvents, which we attribute to photoinduced charge transfer. The mixing of charge transfer with the excitonic state causes accelerated (within 41 ps) decay of the excited state for the directly linked dyad, which is reduced by orders of magnitude with each additional phenyl ring separating the bacteriochlorins. These results highlight the origins of the excited-state dynamics in symmetric BC dyads and provide a new model for studying the primary processes in photosynthesis and for the development of artificial, biomimetic systems for solar energy conversion