Rearrangement of a pyranone to a benzothiazole

The conversion of 2-chloromethyl-5-methoxy-4H-pyran-4-one to 2-amino-5-hydroxy-6-methoxybenzothiazole hydrochloride under mild reaction conditions has been observed. The synthesis of the identical benzothiazole by an alternate unequivocal method is also reported.     

Chlorophosphonates: inexpensive precursors for stereodefined chloro-substituted olefins and unsymmetrical disubstituted acetylenes

New chlorophosphonates bearing a 1,3,2-dioxaphosphorinane ring which are useful for the stereospecific synthesis of 5-chlorofurfuryl substituted olefins and chloro-substituted dienes have been obtained by an easy, inexpensive route. The utility of some of these in the synthesis of ferrocenyl- and anthracenyl-substituted unsymmetrical acetylenes has been explored. The structures of the phosphonates (OCH(2)CMe(2)CH(2)O)P(O)CH(2)(C(4)H(2)ClO) (4) and (OCH(2)CMe(2)CH(2)O)P(O)(CH=CHCH(Cl)Ph (7) have been determined; in addition, the stereochemistry of (5-chlorofurfuryl)CH=CH(4-ClC(6)H(4)) (13b) and 2, 4-Cl(2)C(6)H(3)-CH=CH-CH=C(Ph)Cl (14a) is unambiguously proved by the X-ray structure determination.     

Bidirectional triplet exciton transfer between silicon nanocrystals and perylene

Hybrid materials comprised of inorganic quantum dots functionalized with small-molecule organic chromophores have emerged as promising materials for reshaping light''s energy content. Quantum dots in these structures can serve as light harvesting antennas that absorb photons and pass their energy to molecules bound to their surface in the form of spin-triplet excitons. Energy passed in this manner can fuel upconversion schemes that use triplet fusion to convert infrared light into visible emission. Likewise, triplet excitons passed in the opposite direction, from molecules to quantum dots, can enable solar cells that use singlet fission to circumvent the Shockley–Queisser limit. Silicon QDs represent a key target for these hybrid materials due to silicon''s biocompatibility and preeminence within the solar energy market. However, while triplet transfer from silicon QDs to molecules has been observed, no reports to date have shown evidence of energy moving in the reverse direction. Here, we address this gap by creating silicon QDs functionalized with perylene chromophores that exhibit bidirectional triplet exciton transfer. Using transient absorption, we find triplet transfer from silicon to perylene takes place over 4.2 μs while energy transfer in the reverse direction occurs two orders of magnitude faster, on a 22 ns timescale. To demonstrate this system''s utility, we use it to create a photon upconversion system that generates blue emission at 475 nm using photons with wavelengths as long as 730 nm. Our work shows formation of covalent linkages between silicon and organic molecules can provide sufficient electronic coupling to allow efficient bidirectional triplet exchange, enabling new technologies for photon conversion.

We demonstrate that silicon quantum dots can exchange spin triplet excitons with molecules covalently attached to their surface. Such hybrid materials can enable systems that upconvert incoherent far-red light into the visible spectral range.

Hybrid materials comprised of inorganic quantum dots (QDs) interfaced with small-molecule organic chromophores have emerged as a promising platform for materials that convert near-infrared radiation into the visible spectral range.^1–3 In these structures, QDs act as light-harvesting antennas, absorbing long-wavelength photons and passing their energy to organic molecules bound to their surface in the form of spin-triplet excitons. These excitons can then be transferred into a surrounding medium, typically a solution or thin film, where pairs of them can fuse to form a bright spin-singlet state that can emit a short-wavelength photon.^4–8 Due to the long lifetime of molecular triplet excitons, which can range from several microseconds to milliseconds, these materials can operate at low photon flux, enabling their integration into light-harvesting systems that operate under solar flux^9,10 and limiting heat dissipation during their use in biological applications, such as phototherapy,^11,12 live-cell imaging,^13,14 and optogenetics.¹⁵ These hybrid materials can also be used to study interfacial energy transfer processes fundamental to the operation of solar cells that use triplet fusion''s inverse process, singlet fission, to enhance their performance.^9,16–21 The simplest design for a cell of this type is one that interfaces a singlet fission material directly in line with a back-contacted semiconductor solar cell.^22–24 In these structures, the singlet fission material acts as a light sensitizer that captures high-energy photons and uses their energy to generate pairs of triplet excitons that can be passed to the semiconductor to produce photocurrent. As molecules can be readily attached to QDs via a variety of chemical tethers, these materials allow detailed study of how the structure of the organic:inorganic interface impacts the ability of triplet excitons to move from one material to the other.For both triplet fusion-based light upconversion and singlet fission-based light harvesting, silicon represents a key material of interest. While several upconversion systems have been derived using QDs containing toxic elements, such as Cd^5,7,25 or Pb,^6,8,26,27 Si QDs are nontoxic, making them attractive for biological applications.²⁸ Silicon also dominates the solar energy market, accounting for ∼90% of solar power production,^29,30 making Si:organic interfaces that readily transmit triplet excitons a key design target for singlet fission-based solar cells.^18,19,22 Previously, we have shown triplet exciton transfer from Si QDs to surface-bound anthracene molecules can power a photon upconversion system that operates with 7% efficiency.³¹ However, the inverse energy transfer process that is key for singlet fission devices, triplet exciton transfer from surface-bound molecules to Si, was not observed in our prior work.In this report, we address triplet exciton transfer from molecules to Si by demonstrating a hybrid Si QD:perylene system wherein photoexcitation of the Si QD establishes a spin-triplet exciton population that exists in a dynamic equilibrium between the QD and perylene molecules bound to its surface. While such exciton cycling has been reported for other QD:molecule systems,^32–34 our work represents the first observation of this behavior in Si QD based systems. Using nanosecond transient absorption spectroscopy, we find triplet exciton transfer from Si to perylene takes place on a 4.2 μs timescale while energy transfer in the reverse direction occurs more than two orders of magnitude faster, on a 22 ns timescale. We attribute this difference in energy transfer rates to differences in the exciton density of states between perylene molecules and Si QDs. To demonstrate the utility of triplet excitons produced by this system for photon conversion applications, we have constructed a photon upconversion system by interfacing perylene-functionalized Si QDs with a complementary perylene-based triplet fusion annihilator. We find this system performs well, upconverting radiation with a wavelength as long as 730 nm into blue light centered near 475 nm. Under 532 nm illumination, the system upconverts light with an efficiency of 1.5% under incident light fluxes as low as 80 mW cm⁻². This performance is comparable to that recently demonstrated using the same perylene annihilator coupled with a Pd-porphyrin light absorber.³⁵ Our work demonstrates that the introduction of short, chemical linkers between molecules and Si can enable triplet exciton exchange between these materials for the design of new systems for both photon upconversion and light harvesting.     

β-(5-Pyrimidinyl)ethanolamines

2,4-Diphenyl-5-pyrimidinyl methyl ketone ( 8 ) and 2-phenyl-4-methyl-5-pyrimidinyl phenyl ketone ( 12 ) were prepared by condensation of benzamidine with 2-ethoxymethyl-1-phenyl-1,3-butanedione ( 10 ). Their structures were elucidated by the nmr spectra of their derivative alcohols 13 and 14 , respectively. The ketone 8 was converted by way of the bromoketone 15 to 2-[1-methylethylamino]-1-[2,4-diphenyl-5-pyrimidinyl]ethanol hydrochloride ( 17 ) and 2-amino-1-[2,4-diphenyl-5-pyrimidinyl]ethanol hydrochloride ( 20 ). Pharmacologic testing indicated that 17 and 20 did not possess either antihypertensive or beta adrenergic blocking activities.     

Synthesis and structural assignment of 5,6-dihydro-8-hydroxy-9-methoxy-1H,7H-benzo[ij] quinolizine-1,7-dione

The compound 5,6-dihydro-8-hydroxy-9-methoxy-1H,7H-benzo[ij]quinolizine-1,7-dione ( 4a ) was synthesized from 3-(1,4-dihydro-6,7-dimethoxy-4-oxo-1-quinolyl)propionic acid ( 3a , free base), involving spontaneous demethylation with ring closure. The structural assignment of 4a was based on an analogous, unequivocal synthesis of 5,6-dihydro-9-ethoxy-8-hydroxy-1H,7H-benzo[ij]quinolizine-1,7-dione hydrochloride ( 4b ).     

A study of the catalytic reductive products of 2,3-dihydro-6-methoxy-3-(6-nitroveratrylidene)-4H-benzopyran-4-one. Part II

Although the previously reported (1,2) chemical reduction of 2,3-dihydro-3-(6-nitroveratry-lidene)-4H-benzopyran-4-one with stannous chloride occurred with cyclization to the 6H-[1]-benzopyrano [4,3-b]quinoline ring system, the present study of the catalytic (palladium/carbon) reduction of 2,3-dihydro-6-methoxy-3-(6-nitroveratrylidene)-4H-benzopyran-4-one ( 1 ) (3) has indicated that other products in addition to the expected benzopyranoquinoline ( 3 ) may be isolated, depending upon the conditions of the reduction. The products of the reduction of 1 , isolated and structurally determined, include 2,9,10-trimethoxy-6H-[1]benzopyrano-[4,3-b]quinoline(3),2,9,10-trimethoxy-6a,7,12,12a-tetrahydro-6H-[1]benzopyrano[4,3-b]-quinoline (2), the N-oxide of 3 (6 ), and 6-hydroxy-2,9,10-trimethoxy-6H-[l]benzopyrano-[4,3-b Jquinoline ( 8 ).     

Precise predictions for same-sign W-boson scattering at the LHC

Vector-boson scattering processes are of great importance for the current run-II and future runs of the Large Hadron Collider. The presence of triple and quartic gauge couplings in the process gives access to the gauge sector of the Standard Model (SM) and possible new-physics contributions there. To test any new-physics hypothesis, sound knowledge of the SM contributions is necessary, with a precision which at least matches the experimental uncertainties of existing and forthcoming measurements. In this article we present a detailed study of the vector-boson scattering process with two positively-charged leptons and missing transverse momentum in the final state. In particular, we first carry out a systematic comparison of the various approximations that are usually performed for this kind of process against the complete calculation, at LO and NLO QCD accuracy. Such a study is performed both in the usual fiducial region used by experimental collaborations and in a more inclusive phase space, where the differences among the various approximations lead to more sizeable effects. Afterwards, we turn to predictions matched to parton showers, at LO and NLO: we show that on the one hand, the inclusion of NLO QCD corrections leads to more stable predictions, but on the other hand the details of the matching and of the parton-shower programs cause differences which are considerably larger than those observed at fixed order, even in the experimental fiducial region. We conclude with recommendations for experimental studies of vector-boson scattering processes.     

Observation of the Low‐Frequency Spectrum of the Water Dimer as a Sensitive Test of the Water Dimer Potential and Dipole Moment Surfaces

Using the helium nanodroplet isolation setup at the ultrabright free‐electron laser source FELIX in Nijmegen (BoHeNDI@FELIX), the intermolecular modes of water dimer in the frequency region from 70 to 550 cm^?1 were recorded. Observed bands were assigned to donor torsion, acceptor wag, acceptor twist, intermolecular stretch, donor torsion overtone, and in‐plane and out‐of‐plane librational modes. This experimental data set provides a sensitive test for state‐of‐the‐art water potentials and dipole moment surfaces. Theoretical calculations of the IR spectrum are presented using high‐level quantum and approximate quasiclassical molecular dynamics approaches. These calculations use the full‐dimensional ab initio WHHB potential and dipole moment surfaces. Based on the experimental data, a considerable increase of the acceptor switch and a bifurcation tunneling splitting in the librational mode is deduced, which is a consequence of the effective decrease in the tunneling barrier.     

Palladium catalyzed cross-coupling reactions for phosphorus-carbon bond formation

Underappreciated in the realm of palladium catalyzed cross-coupling chemistry is the formation of phosphorous-carbon bonds. This tutorial review summarises a collection of important contributions in the area, providing a flavour of the many types of phosphorus species that are participants in palladium catalyzed phosphorus-carbon bond formation. Recent developments include the usage of the cross-coupling reaction for preparation of phosphine ligands and the involvement of low molecular weight phosphinic acid derivatives for the synthesis of unsaturated phosphinic and phosphonic acid derivatives. Mechanistic cycles are offered in some instances. Stereochemical issues are addressed where applicable. The literature is covered to mid 2003.     

Development of an optically pure In b-diketonate for the scintillator of an 115In-loaded solar neutrino detector

We report on the development of a novel In-loaded scintillator for a next generation low energy solar neutrino detector that would be based on neutrino interactions with ¹¹⁵In. In particular, -diketone complexes added to organic scintillating solvents are investigated. Here we describe details of the chemical synthesis and unique purification steps for specific indium--diketonates that we developed so as to achieve the main properties needed for such an experiment: optical transparency, chemical stability and high solubility in a scintillator solvent. Together with suitably adjusted fluors, we find that notable light yields are possible.