Publications by authors named "Simon Lotz"

We demonstrate large-area robotically assisted optical coherence tomography (LARA-OCT), utilizing a seven-degree-of-freedom robotic arm in conjunction with a 3.3 MHz swept-source OCT to raster scan samples of arbitrary shape. By combining multiple fields of view (FOV), LARA-OCT can probe a much larger area than conventional OCT.

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This paper presents a Fourier domain mode locked (FDML) laser centered around 840 nm. It features a bidirectional sweep repetition rate of 828 kHz and a spectral bandwidth of 40 nm. An axial resolution of ∼9.

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Colonoscopy and endoscopic ultrasound play pivotal roles in the assessment of rectal diseases, especially rectal cancer and inflammatory bowel diseases. Optical coherence tomography (OCT) offers a superior depth resolution, which is a critical factor for individualizing the therapeutic concept and evaluating the therapy response. We developed two distinct rectoscope prototypes, which were integrated into a 1300 nm MHz-OCT system constructed at our facility.

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Four-wave mixing (FWM) enables the generation and amplification of light in spectral regions where suitable fiber gain media are unavailable. The 1300 nm and 900 nm regions are of especially high interest for time-encoded (TICO) stimulated Raman scattering microscopy and spectro-temporal laser imaging by diffracted excitation (SLIDE) two-photon microscopy. We present a new, to the best of our knowledge, FWM setup where we shift the power of a home-built fully fiber-based master oscillator power amplifier (MOPA) at 1064 nm to the 1300-nm region of a rapidly wavelength-sweeping Fourier domain mode-locked (FDML) laser in a photonic crystal fiber (PCF) creating pulses in the 900-nm region.

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We present continuous three-dimensional spectral zooming in live 4D-OCT using a home-built FDML based OCT system with 3.28 MHz A-scan rate. Improved coherence characteristics of the FDML laser allow for imaging ranges up to 10 cm.

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Sulfoximines, the next generation systemic insecticides developed to replace neonicotinoids, have been shown to negatively impact pollinator development and reproduction. However, field-realistic studies on sulfoximines are few and consequences on pollination services unexplored. Moreover, the impacts of other agrochemicals such as fungicides, and their combined effects with insecticides remain poorly investigated.

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In highly dispersion compensated Fourier domain mode locked (FDML) lasers, an ultra-low noise operation can only be achieved by extremely precise and stable matching of the filter tuning period and light circulation time in the cavity. We present a robust and high precision closed-loop control algorithm and an actively cavity length controlled FDML laser. The cavity length control achieves a stability of ∼0.

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Two (thieno[3,2-b]thiophene) and three annulated thiophenes (dithieno[2,3-b;3',2'-d]thiophene and dithieno[3,2-b;2',3'-d]thiophene) were employed as building blocks to synthesize linear or semi-circular chelated mononuclear biscarbene and dinuclear tetracarbene complexes. The electronic properties of the annulated thienylene chelated carbene complexes were investigated by cyclic voltammetry experiments and compared to non-chelated Fischer-type monocarbene complexes. Density functional theory (DFT) calculations were used to assign the redox events and to probe the extent of electron delocalisation as well as the possibility of electronic (intramolecular metal-metal) communication as a result of intervalence.

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The oxidative cleaving of a rhenium-rhenium bond by bromine in binuclear Fischer carbene complexes proves to be an effective method to prepare mononuclear bromido-carbene complexes. The reaction of mono- and dilithiated thieno[2,3-b]thiophene (2,3-b-TTH) and thieno[3,2-b]thiophene (3,2-b-TTH) with [Re(CO)] affords dirhenium nonacarbonyl ethoxycarbene complexes, [Re(CO){C(OEt)2,3-b-TTH}] (1a) and [Re(CO){C(OEt)3,2-b-TTH}] (1b), and the tetrarhenium bis(ethoxycarbene) complexes from the dilithiated thiophene substrates, [Re(CO)-μ-{C(OEt)-2,3-b-TT-C(OEt)}Re(CO)] (2a) and [Re(CO)-μ-{C(OEt)-3,2-b-TT-C(OEt)}Re(CO)] (2b) featuring bridging thiophene linkers. Rhenium-rhenium bond cleavage by bromine of the monocarbene complexes yielded the scarce class of monorhenium bromido-carbene complexes, cis-[Re(CO){C(OEt)2,3-b-TTH}Br] (3a) and cis-[Re(CO){C(OEt)3,2-b-TTH}Br] (3b), while the corresponding reaction of the biscarbene tetrarhenium carbonyl complex of thieno[2,3-b]thiophene afforded the cleaving of both metal-metal bonds to give the novel dirhenium biscarbene dibromido complex with a thienothiophene spacer, [Re(CO)Br-μ-{C(OEt)-2,3-b-TT-C(OEt)}Re(CO)Br] (4a).

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Access to multicarbene complexes of a fused thienothiophene substrate was obtained by the use of the tetrabrominated thieno[2,3-b]thiophene precursor in a lithium-bromide exchange reaction, followed by nucleophilic attack on metal hexacarbonyls (M = Cr, W). Subsequent alkylation afforded unique triscarbene complexes [M(CO)4{{C(OEt)}2C6H1S2C(OEt)}M(CO)5] (M = Cr 12, W 13) featuring three non-equivalent carbene ligands on a single thiophene linker, as well as the bischelated tetracarbene complexes [M(CO)4{{C(OEt)}2C6S2{C(OEt)}2}M(CO)4] (M = Cr 14, W 15). The triscarbene complexes 12 and 13 are the first examples of multi-alkoxycarbene complexes featuring three non-equivalent carbene ligands.

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Reaction of mono- and dilithiated thiophene (a), bithiophene (b) and 2,5-dibromothiophene (c) with [Re(2)(CO)(10)] afforded, after subsequent alkylation with triethyloxonium tetrafluoroborate, tetra- and binuclear Fischer carbene complexes, [Re(2)(CO)(9){C(OEt){C(4)H(2)S}(n)X}], n = 1, X = H (1a); n = 2, X = H (1b); n = 1, X = Br (1c); n = 1, X = C(OEt)Re(2)(CO)(9), (2a); n = 2, X = C(OEt)Re(2)(CO)(9) (2b), as major products. The dirhenium acylate intermediates from this reaction not only gave the expected novel ethoxycarbene complexes with alkylation but after rhenium-rhenium bond breaking afforded a number of minor products. The (1)H NMR spectrum of the crude reaction mixture revealed the formation of four metal hydride complexes and aldehydes.

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Fischer carbene complexes of the group VII transition metals (Mn and Re) containing at least two or three different transition metal substituents, all in electronic contact with the carbene carbon atom, were synthesized. The structural features and their relevance to bonding in the carbene multimetal compounds were investigated, as they represent indicators of possible reactivity sites in polymetallic carbene assemblies. For complexes of the type [ML(x){C(OR)R'}] (ML(x) = MnCp(CO)(2) or Re(2)(CO)(9)), ferrocenyl (Fc) was chosen as the R' substituent, while the OR substituent was systematically varied between an ethoxy or a titanoxy group, to yield the complexes 1a (ML(x) = MnCp(CO)(2), R = Et, R' = Fc), 2a (ML(x) = MnCp(CO)(2), R = TiCp(2)Cl, R' = Fc), 3a (ML(x) = Re(2)(CO)(9), R = Et, R' = Fc), and 4a (ML(x) = Re(2)(CO)(9), R = TiCp(2)Cl, R' = Fc).

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The activation of a section, or of all the carbons of thiophene by bromine in lithium-halogen exchange reactions, was implemented in a step-wise manner to facilitate the preparation of novel multiple Fischer carbene-bearing thiophene compounds.

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Mono- and binuclear Fischer carbene complexes, [M(CO)5{C(OR)Ar-ArX}], X = H, {C(OR)M'(CO)5}; M, M' = W or Cr; R = Me, Et or (CH2)4OMe; Ar = thiophene, N-methylpyrrole or furan units 1-20, were synthesized. For this purpose, mono-, bi- or stepwise lithiated bithiophene, N,N'-dimethylbipyrrole, thienylfuran and N-methyl(thienyl)pyrrole were reacted with chromium and tungsten hexacarbonyl precursors. Dilithiation in the 2- and 9-positions of N-methyl(thienyl)pyrrole could not be achieved.

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Carbene complexes of chromium and tungsten with a bridging furan substituent were synthesized from lithiated furan precursors and metal hexacarbonyls. The binuclear biscarbene complexes [(CO)5M{C(OEt)-C4H2O-C(OEt)}M'(CO)5](M = M'= Cr (3), W (4)) were obtained as well as the corresponding monocarbene complexes [M{C(OEt)-C(4)H3O}(CO)5](M = Cr (1), W (2)). A method of protecting the carbene moiety during the metal acylate stage was used to increase not only the yields of the binuclear Fischer biscarbene complexes 3 and 4 but to establish a method to synthesize analogous mixed heterobinuclear carbene complexes (M = W, M'= Cr (5)) in high yields.

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