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We report on the triplet sensitization of the intramolecular Photo-Dehydro-Diels-Alder (PDDA) reaction of two diaryl suberates bearing methyl propiolate chromophors. Compared with the non-sensitized irradiation, considerably increased yields could be observed.
Moreover, it is possible to use the more efficient UVA lamps instead of UVB lamps.
Among three investigated sensitizers (xanthone, benzophenone, thioxanthone) xanthone gave the best results.
The replacement of oxygen by sulfur atoms of [1,3]-dioxolo[4.5-f]benzodioxole (DBD) fluorescent dyes is an efficient way to adjust the photophysical properties (sulfur tuning). While previously developed S-4-DBD dyes exhibit considerably red-shifted absorption and emission wavelength, the heavy atom effect of four sulfur atoms cause low fluorescence quantum yields and short fluorescence lifetimes. Herein, we demonstrate that the replacement of less than four sulfur atoms (S-1-DBD, 1,2-S-2-DBD, and 1,4-S-2-DBD dyes) permits a fine-tuning of the photophysical properties. In some cases, a similar influence on the wavelength without the detrimental effect on the quantum yields and lifetimes is observed. Furthermore, the synthetic accessibility of S-1- and S-2-DBD dyes is improved, compared with S-4-DBD dyes. For coupling with biomolecules a series of reactive derivatives of the new dyes were developed (azides, OSu esters, alkynes, maleimides).
Carbon nanodots revised
(2020)
Luminescent compounds obtained from the thermal reaction of citric acid and urea have been studied and utilized in different applications in the past few years. The identified reaction products range from carbon nitrides over graphitic carbon to distinct molecular fluorophores. On the other hand, the solid, non-fluorescent reaction product produced at higher temperatures has been found to be a valuable precursor for the CO2-laser-assisted carbonization reaction in carbon laser-patterning. This work addresses the question of structural identification of both, the fluorescent and non-fluorescent reaction products obtained in the thermal reaction of citric acid and urea. The reaction products produced during autoclave-microwave reactions in the melt were thoroughly investigated as a function of the reaction temperature and the reaction products were subsequently separated by a series of solvent extractions and column chromatography. The evolution of a green molecular fluorophore, namely HPPT, was confirmed and a full characterization study on its structure and photophysical properties was conducted. The additional blue fluorescence is attributed to oligomeric ureas, which was confirmed by complementary optical and structural characterization. These two components form strong hydrogen-bond networks which eventually react to form solid, semi-crystalline particles with a size of similar to 7 nm and an elemental composition of 46% C, 22% N, and 29% O. The structural features and properties of all three main components were investigated in a comprehensive characterization study.
An efficient method for the preparation of arylnaphthalene lignans (ANLs) was developed, which is based on thePhoto-Dehydro-DIELS-ALDER(PDDA) reaction. While intermolecular PDDA reactions turned out to be inefficient, theintramolecular variant using suberic acid as tether linking two aryl propiolic esters smoothly provided naphthalenophanes. Theirradiations were performed with a previously developed annular continuous-flow reactor and UVB lamps. In this way, the naturalproducts Alashinol D, Taiwanin C, and an unnamed ANL could be prepared.
The so-called DBD ([1,3]dioxolo[4,5-f][1,3]benzodioxole) dyes are a new class of fluorescent dyes, with tunable photophysical properties like absorption, fluorescence lifetime, and Stokes shift. With the development of sulfur based DBDs, this dye class is extended even further for possible applications in spectroscopy and microscopy. In this paper we are investigating the basic photophysical properties and their implications for future applications for S-4-DBD as well as O-4-DBD. On the basis of time-resolved laser fluorescence spectroscopy, transient absorption spectroscopy, and UV/vis-spectroscopy, we determined the rate constants of the radiative and nonradiative deactivation processes as well as the energy of respective electronic states involved in the electronic deactivation of S-4-DBD and of O-4-DBD. For S-4-DBD we unraveled the triplet formation with intersystem crossing quantum yields of up to 80%. By TD-DFT calculations we estimated a triplet energy of around 13500-14700 cm(-1) depending on the DBD dye and solvent. Through solvent dependent measurements, we found quadrupole moments in the range of 2 B.
We report on a further development of [1,3]-dioxolo[4.5-f]benzodioxole (DBD) fluorescent dyes by replacement of the four oxygen atoms of the heterocyclic core by sulfur atoms. This variation causes striking changes of the photophysical properties. Whereas absorption and emission significantly shifted to longer wavelength, the fluorescence lifetimes and quantum yields are diminished compared to DBD dyes. The latter effect is presumably caused by an enhanced intersystem crossing to the triplet state due to the sulfur atoms. The very large Stokes shifts of the S-4-DBD dyes ranging from 3000 cm(-1) to 7400 cm(-1) (67 nm to 191 nm) should be especially emphasized. By analogy with DBD dyes a broad variation of absorption and emission wavelength is possible by introducing different electron withdrawing substituents. Moreover, some derivatives for coupling with biomolecules were developed.
The replacement of oxygen by sulfur atoms of [1,3]-dioxolo[4.5-f]benzodioxole (DBD) fluorescent dyes is an efficient way to adjust the photophysical properties (sulfur tuning). While previously developed S-4-DBD dyes exhibit considerably red-shifted absorption and emission wavelength, the heavy atom effect of four sulfur atoms cause low fluorescence quantum yields and short fluorescence lifetimes. Herein, we demonstrate that the replacement of less than four sulfur atoms (S-1-DBD, 1,2-S-2-DBD, and 1,4-S-2-DBD dyes) permits a fine-tuning of the photophysical properties. In some cases, a similar influence on the wavelength without the detrimental effect on the quantum yields and lifetimes is observed. Furthermore, the synthetic accessibility of S-1- and S-2-DBD dyes is improved, compared with S-4-DBD dyes. For coupling with biomolecules a series of reactive derivatives of the new dyes were developed (azides, OSu esters, alkynes, maleimides).
The photochemical fragmentation of N-aroylsulfonamides 9 (ASAP) is a powerful method for the preparation of various biaryls. Compounds 9 are easily accessible in two steps from amines by treatment with arenesulfonyl chlorides and aroyl chlorides. Many of these compounds were prepared for the first time. The irradiation takes place in a previously developed continuous-flow reactor using inexpensive UVB or UVC fluorescent lamps. Isocyanates and sulphur dioxide are formed as the only by-products. The ASAP tolerates a variety of functional groups and is even suited for the preparation of phenylnaphthalenes and terphenyls. The ASAP mechanism was elucidated by interaction of photophysical and quantum chemical (DFT) methods and revealed a spirocyclic biradical as key intermediate.
Class IIa histone deacetylases (HDACs) show extremely low enzymatic activity and no commonly accepted endogenous substrate is known today. Increasing evidence suggests that these enzymes exert their effect rather through molecular recognition of acetylated proteins and recruiting other proteins like HDAC3 to the desired target location. Accordingly, class IIa HDACs like bromodomains have been suggested to act as “Readers” of acetyl marks, whereas enzymatically active HDACs of class I or IIb are called “Erasers” to highlight their capability to remove acetyl groups from acetylated histones or other proteins. Small-molecule ligands of class IIa histone deacetylases (HDACs) have gained tremendous attention during the last decade and have been suggested as pharmaceutical targets in several indication areas such as cancer, Huntington's disease and muscular atrophy. Up to now, only enzyme activity assays with artificial chemically activated trifluoroacetylated substrates are in use for the identification and characterization of new active compounds against class IIa HDACs. Here, we describe the first binding assay for this class of HDAC enzymes that involves a simple mix-and-measure procedure and an extraordinarily robust fluorescence lifetime readout based on [1,3]dioxolo[4,5-f]benzodioxole-based ligand probes. The principle of the assay is generic and can also be transferred to class I HDAC8.
Synthetic routes to a collection of new fluorescent dyes are described, which are based on the [1,3]-dioxolo[4.5-f]benzodioxole (DBD) core. By introducing different electron withdrawing groups in 4- and 8-position of the DBD moiety the emission wavelength could be adjusted over a large spectral range from blue to orange light.