Rationalization of excited-state tuning through ultrafast transient absorption and vibrational coherence spectroscopy

Photophysical and-chemical processes make use of light as strongly quantized energy source, rendering mechanisms possible, which involve excited states that are thermally unavailable. This puts them at the heart of many exciting and promising technologies from photovoltaics to photocatalysis and photodynamic therapy. In this work, several strategies to tuning these excited states are rationalized by ultrafast transient absorption and impulsive vibrational spectroscopy, applied to two different classes of samples. Firstly, the excited-state dynamics of two iron(II) complexes are investigated for the tuning effect of solvent choice and ligand design. They toggle on and off the involvement of metal-centered (MC) excited states acting as loss channels for desired metal-to-ligand charge transfer (MLCT) states. Impulsive vibrational spectroscopy is established as suitable method for identifying MLCT-MC transitions in [Fe(bpy)(CN)4]2-, a well-known reference sample. The method is then applied to an iron(II)N-heterocyclic carbene complex and identifies an ultrafast MLCT-MC branching in this promising dye-sensitizer candidate. Secondly, the photophysics and -chemistry of triphenylamine is thoroughly investigated for the influences of solvent, the oxygen content therein and enforced planarity. In n-hexane, triphenylamine is converted to N-phenylcarbazole, with oxygen playing an intricate double role. The conversion is stopped completely by planarization due to the cancellation of p-orbital preorientation. In chloroform, ultrafast electron transfer to the solvent dominates the photochemistry, producing the radical cation leading to chromophore dimerization

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Dolores “Del” Hainer, interviewed by Rebecca Pelletier and Elizabeth Fowler, Part 2

Dolores “Del” (Theriault) Hainer, interviewed by Rebecca Pelletier and Elizabeth Fowler, November 10, 2000, Hampden, Maine. Hainer talks about joining the army after World War II; her basic training in Camp Lee, VA; and being stationed in San Antonio, TX. Text: 34 pp. transcript. Time: 1 hour 17 minutes. Listen: Part 1: mfc_na3201_c2301_01 Part 2: mfc_na3201_c2301_02https://digitalcommons.library.umaine.edu/mf144/1002/thumbnail.jp

Dolores “Del” Hainer, interviewed by Rebecca Pelletier and Elizabeth Fowler, Part 1

Dolores “Del” (Theriault) Hainer, interviewed by Rebecca Pelletier and Elizabeth Fowler, November 10, 2000, Hampden, Maine. Hainer talks about joining the army after World War II; her basic training in Camp Lee, VA; and being stationed in San Antonio, TX. Text: 34 pp. transcript. Time: 1 hour 17 minutes. Listen: Part 1: mfc_na3201_c2301_01Part 2: mfc_na3201_c2301_02https://digitalcommons.library.umaine.edu/mf144/1001/thumbnail.jp

Quantitative measurement of combustion gases in harsh environments using NDIR spectroscopy

The global climate change calls for a more environmental friendly use of energy and has led to stricter limits and regulations for the emissions of various greenhouse gases. Consequently, there is nowadays an increasing need for the detection of exhaust and natural gases. This need leads to an ever-growing market for gas sensors, which, at the moment, is dominated by chemical sensors. Yet, the increasing demands to also measure under harsh environmental conditions pave the way for non-invasive measurements and thus to optical detection techniques. Here, we present the development of a non-dispersive infrared absorption spectroscopy (NDIR) method for application to optical detection systems operating under harsh environments.Comment: 10 pages, 8 figure

Determining gene expression control during neural differentiation through coupled protein localization and RNA-seq in single cells

Although the primary sequence of the eukaryotic genome is largely invariant across cells in an organism, the expression of genes is tightly regulated: specific complements and levels of expressed genes define the identity and function of cells. A primary mechanism of gene expression control is at the level of access to DNA sequences that can direct expression of individual genes. Access to these DNA regulatory elements is established and maintained by the combinatorial binding of an immense repertoire of transcription factors (TFs) and chromatin regulators which function together to drive cell-type-specific gene expression. There is a range of cell heterogeneity that enables distinct expression levels within a tissue or population of cells, establishing average expression within the population but conferring different properties on individual cells. Importantly, the level of gene expression heterogeneity across single cells has only recently become clear through technological innovations that have permitted the development of single-cell genomic assays