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The surfaces of colloidal nanocrystals are frequently passivated with carboxylate ligands that exert significant effects on their optoelectronic properties and chemical stability. The binding geometries of these ligands are often experimentally investigated using vibrational spectroscopy, but the interpretation of the IR signal is usually not trivial. Here, using machine-learning (ML) algorithms trained on DFT data, we simulate an IR spectrum of a lead-rich PbS nanocrystal passivated with butyrate ligands. We obtain good agreement with the experimental signal and demonstrate that the observed line shape stems from a very wide range of “tilted-bridge”-type geometries and does not indicate the coexistence of “bridging” and “chelating” binding modes as has been previously assumed. This work illustrates the limitations of empirical spectrum assignment and demonstrates the effectiveness of ML-driven molecular dynamics simulations in reproducing the IR spectra of nanoscopic systems. 

The lack of a detailed mechanistic understanding for plasmon-mediated charge transfer at metal-semiconductor interfaces severely limits the design of efficient photovoltaic and photocatalytic devices. A major remaining question is the relative contribution from indirect transfer of hot electrons generated by plasmon decay in the metal to the semiconductor compared to direct metal-to-semiconductor interfacial charge transfer. Here, we demonstrate an overall electron transfer efficiency of 44 ± 3% from gold nanorods to titanium oxide shells when excited on resonance. We prove that half of it originates from direct interfacial charge transfer mediated specifically by exciting the plasmon. We are able to distinguish between direct and indirect pathways through multimodal frequency-resolved approach measuring the homogeneous plasmon linewidth by single-particle scattering spectroscopy and time-resolved transient absorption spectroscopy with variable pump wavelengths. Our results signify that the direct plasmon-induced charge transfer pathway is a promising way to improve hot carrier extraction efficiency by circumventing metal intrinsic decay that results mainly in nonspecific heating. 

A major challenge in the “bottom-up” solvothermal synthesis of carbon dots (CDs) is the removal of small-molecule byproducts, noncarbonized polyamides, or other impurities that confound the optical properties. In previously reported benzene diamine-based CDs, the observed fluorescence signal already has been shown to arise from free small molecules, not from nanosized carbonized dots. Here we have unambiguously identified the small-molecule species in the synthesis of CDs starting with several isomers of benzene diamine by directly matching their NMR, mass spectrometry, and optical data with commercially available small organic molecules. By combining dialysis and chromatography, we have sufficiently purified the CD reaction mixtures to measure the CD size by TEM and STM, elemental composition, optical absorption and emission, and single-particle blinking dynamics. The results can be rationalized by electronic structure calculations on small model CDs. Our results conclusively show that the purified benzene diamine-based CDs do not emit red fluorescence, so the quest for full-spectrum fluorescence from isomers of a single precursor molecule remains open. 

Salicylideneaniline (SA) is an archetypal system for excited-state intramolecular proton transfer (ESIPT) in non-planar systems. Multiple channels for relaxation involving both the keto and enol forms have been proposed after excitation to S1 with near-UV light. Here, we present transient absorption measurements of hot gas-phase SA, jet-cooled SA, and SA in Ar clusters using cavity-enhanced transient absorption spectroscopy (CE-TAS). Assignment of the spectra is aided by simulated TAS spectra, computed by applying time-dependent complete active space configuration interaction (TD-CASCI) to structures drawn from nonadiabatic molecular dynamics simulations. We find prompt ESIPT in all conditions followed by the rapid generation of the trans keto metastable photochrome state and fluorescent keto state in parallel. Increasing the internal energy increases the photochrome yield and decreases the fluorescent yield and fluorescent state lifetime observed in TAS. In Ar clusters, internal conversion of SA is severely hindered, but the photochrome yield is unchanged. Taken together, these results are consistent with the photochrome being produced via the vibrationally excited keto population after ESIPT. 

Abstract A facile and efficient two‐step synthesis ofp‐substituted tris(2‐pyridylmethyl)amine (TPMA) ligands to form Cu complexes with the highest activity to date in atom transfer radical polymerization (ATRP) is presented. In the divergent synthesis,p‐Cl substituents in tris(4‐chloro‐2‐pyridylmethyl)amine (TPMA^3Cl) were replaced in one step and high yield by electron‐donating cyclic amines (pyrrolidine (TPMA^PYR), piperidine (TPMA^PIP), and morpholine (TPMA^MOR)) by nucleophilic aromatic substitution. The [Cu^II(TPMA^NR2)Br]⁺complexes exhibited larger energy gaps between frontier molecular orbitals and >0.2 V more negative reduction potentials than [Cu^II(TPMA)Br]⁺, indicating >3 orders of magnitude higher ATRP activity. [Cu^I(TPMA^PYR)]⁺exhibited the highest reported activity for Br‐capped acrylate chain ends in DMF, and moderate activity toward C−F bonds at room temperature. ATRP ofn‐butyl acrylate using only 10–25 part per million loadings of [Cu^II(TPMA^NR2)Br]⁺exhibited excellent control.