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  1. Abstract

    3‐Point annulations, or phenalenannulations, transform a benzene ring directly into a substituted pyrene by “wrapping” two new cycles around the perimeter of the central ring at three consecutive carbon atoms. This efficient, modular, and general method for π‐extension opens access to non‐symmetric pyrenes and their expanded analogues. Potentially, this approach can convert any aromatic ring bearing a ‐CH2Br or a ‐CHO group into a pyrene moiety. Depending upon the workup choices, the process can be directed towards either tin‐ or iodo‐substituted product formation, giving complementary choices for further various cross‐coupling reactions. The two‐directional bis‐double annulation adds two new polyaromatic extensions with a total of six new aromatic rings at a central core.

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  2. Intermolecular interactions on inorganic substrates can have a critical impact on the electrochemical and photophysical properties of the materials and subsequent performance in hybrid electronics. Critical to the intentional formation or inhibition of these processes is controlling interactions between molecules on a surface. In this report, we investigated the impact of surface loading and atomic-layer-deposited Al2O3 overlayers on the intermolecular interactions of a ZrO2-bound anthracene derivative as probed by the photophysical properties of the interface. While surface loading density had no impact on the absorption spectra of the films, there was an increase in excimer features with surface loading as observed by both emission and transient absorption. The addition of ALD overlayers of Al2O3 resulted in a decrease in excimer formation, but the emission and transient absorption spectra were still dominated by excimer features. These results suggest that ALD may provide a post-surface loading means of influencing such intermolecular interactions. 
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    Free, publicly-accessible full text available June 1, 2024
  3. Metal ion-linked multilayers have emerged as a simple and modular means of assembling molecular components on an inorganic substrate. The choice of molecules, based on their excited state energies and redox potentials, has enabled the directional control of energy and electron transfer events for application in electrochromics, solar energy harvesting, molecular rectifiers, photocatalysis, and more. Here, we recount the more than 35-year journey of metal ion-linked multilayers and their transition from planar to mesoporous substrates and from homogeneous to heterogeneous multilayers. This includes showcasing the vast range of components (i.e., substrates, metal ions, and molecules), structural insights, and applications. We also highlight current limitations in our knowledge of and ability to control these systems which must be overcome to realize the full potential of metal ion-linked multilayers. 
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  4. Triplet–triplet annihilation upconversion (TTA-UC) is a process that shows promise for applications such as energy-harvesting and light-generation technologies. The irradiance dependent performance of TTA-UC systems is typically gauged using a graphical analysis, rather than a detailed model. Additionally, kinetic models for TTA-UC rarely incorporate mass conservation, which is a phenomenon that can have important consequences under experimentally relevant conditions. We present an analytical, mass-conserving kinetic model for TTA-UC, and demonstrate that the mass-conservation constraint cannot generally be ignored. This model accounts for saturation in TTA-UC data. Saturation complicates the interpretation of the threshold irradiance I th , a popular performance metric. We propose two alternative figures of merit for overall performance. Finally, we show that our model can robustly fit experimental data from a wide variety of sensitized TTA-UC systems, enabling the direct and accurate determination of I th and of our proposed performance metrics. We employ this fitting procedure to benchmark and compare these metrics, using data from the literature. 
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  5. Ruthenium polypyridyl complexes have gained significant interest as photochemotherapies (PCTs) where their excited-state properties play a critical role in the photo-cytotoxicity mechanism and efficacy. Herein we report a systematic electrochemical, spectrochemical, and photophysical analysis of a series of ruthenium( ii ) polypyridyl complexes of the type [Ru(bpy) 2 (N–N)] 2+ (where bpy = 2,2′-bipyridine; N–N is a bidentate polypyridyl ligand) designed to mimic PCTs. In this series, the N–N ligand was modified through increased conjugation and/or incorporation of electronegative heteroatoms to shift the metal-to-ligand charge-transfer (MLCT) absorptions near the therapeutic window for PCTs (600–1100 nm) while incorporating steric bulk to trigger photoinduced ligand dissociation. The lowest energy MLCT absorptions were red-shifted from λ max = 454 nm to 564 nm, with emission energies decreasing from λ max = 620 nm to 850 nm. Photoinduced ligand ejection and temperature-dependent emission studies revealed an important interplay between red-shifting MLCT absorptions and accessing the dissociative 3 dd* states, with energy barriers between the 3 MLCT* and 3 dd* states ranging from 850 cm −1 to 2580 cm −1 for the complexes measured. This work demonstrates the importance of understanding both the MLCT manifold and 3 dd* state energy levels in the future design of ligands and complexes for PCT. 
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  6. Integrating molecular photon upconversion via triplet–triplet annihilation (TTA-UC) directly into a solar cell offers a means of harnessing sub-bandgap, near infrared (NIR) photons and surpassing the Shockley–Queisser limit. However, all integrated TTA-UC solar cells to date only harness visible light. Here, we incorporate an osmium polypyridal complex (Os) as the triplet sensitizer in a metal ion linked multilayer photoanode that is capable of harnessing NIR light via S 0 to T 1 * excitation, triple energy transfer to a phosphonated bis(9,10-diphenylethynyl)anthracene annihilator (A), TTA-UC, and electron injection into TiO 2 from the upcoverted state. The TiO 2 -A-Zn-Os devices have five-fold higher photocurrent (∼3.5 μA cm −2 ) than the sum of their parts. IPCE data and excitation intensity dependent measurements indicate that the NIR photons are harvested through a TTA-UC mechanism. Transient absorption spectroscopy is used to show that the low photocurrent, as compared to visible light harnessing TTA-UC solar cells, can be atributed to: (1) slow sensitizer to annihilator triplet energy transfer, (2) a low injection yield for the annihilator, and (3) fast back energy transfer from the upconverted state to the sensitizer. Regardless, these results serve as a proof-of-concept that NIR photons can be harnessed via an S 0 to T 1 * sensitizer excited, integrated TTA-UC solar cell and that further improvements can readily be made by remedying the performance limiting processes noted above. 
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