Seven derivatives of 1,2-dicarbadodecaborane (ortho-carborane, 1,2-C(2)B(10)H(12)) with a 1,3-diethyl- or 1,3-diphenyl-1,3,2-benzodiazaborolyl group on one cage carbon atom were synthesized and structurally characterized. Six of these compounds showed remarkable low-energy fluorescence emissions with large Stokes shifts of 15100-20260 cm(-1) and quantum yields (Φ(F)) of up to 65% in the solid state. The low-energy fluorescence emission, which was assigned to a charge-transfer (CT) transition between the cage and the heterocyclic unit, depended on the orientation (torsion angle, ψ) of the diazaborolyl group with respect to the cage C-C bond. In cyclohexane, two compounds exhibited very weak dual fluorescence emissions with Stokes shifts of 15660-18090 cm(-1) for the CT bands and 1960-5540 cm(-1) for the high-energy bands, which were assigned to local transitions within the benzodiazaborole units (local excitation, LE), whereas four compounds showed only CT bands with Φ(F) values between 8-32%. Two distinct excited singlet-state (S(1)) geometries, denoted S(1)(LE) and S(1)(CT), were observed computationally for the benzodiazaborolyl-ortho-carboranes, the population of which depended on their orientation (ψ). TD-DFT calculations on these excited state geometries were in accord with their CT and LE emissions. These C-diazaborolyl-ortho-carboranes were viewed as donor-acceptor systems with the diazaborolyl group as the donor and the ortho-carboranyl group as the acceptor.

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Static and time-resolved fluorescence studies were carried out to investigate the photophysical properties and fluoride sensing abilities of highly fluorescent thienyl-containing 1,3-diethyl-1,3,2-benzodiazaboroles. Absorption and fluorescence spectra were measured in various solvents, showing the fluorophores to emit in the visible wavelength region with colors varying from blue to orange and quantum yields ranging between 0.21 and 1. Measured Stokes shifts of 2898 cm(-1) to 9308 cm(-1) were used to calculate the difference between excited- and ground-state dipole moments of the fluorophores. Values up to 18.8 D are of the same magnitude as for designed polarity probes such as PRODAN, supporting the idea of internal charge transfer transitions. Quenching studies with pyridine observing static and time-resolved fluorescence revealed a purely dynamic quenching mechanism and low Lewis acidity of the boron within the benzodiazaborolyl moiety compared to other triarylboranes. In contrast to this, quenching with fluoride was shown to stem from adduct formation. Reversible complexation of fluoride follows a simple mechanism for multi-functionalized benzodiazaboroles 2b and 2c, while those containing only one benzodiazaborole moiety (1 and 2a) show a more complicated behaviour, which might be explained by aggregation. Combining a benzodiazaborole group and a dimesitylborane function results in spectrally switchable fluoride sensors 3a and 3b, since the two boron sides can be deactivated for fluorescence in a stepwise manner.

Solution processing methods of conjugated polymers are an important strategy for the preparation of organic semiconductors. We introduce a novel family of semiconductors prepared by the solution based small molecule self-assembly of 2-amino-5-pentafluorophenylpyrimidine and various silver(I) salts (AgX; X = CO 2 CF 3 , SO 3 CF 3 , NO 3 ). The compounds are analyzed by single crystal analysis revealing that the solid state assembly consists of alternating polymer strands of 2-aminopyrimidine and silver(I).The solid state assembly can be controlled by the silver counterion and the solvent yielding polymer strands with different interatomic parameters and optoelectrical properties. The compounds are optically characterized and reveal remarkably different solid state absorption when compared to the parent compound 2-aminopyrimidine in solution. Also, an exclusive solid state emissive state is observed. Herein, the excitation occurs not at the maximum but at the onset of absorbance. The silver(I)triflate-2-aminopyrimidine yields two different porous frameworks depending on the solvent used for crystallization. These porous frameworks are made of 1-dimensional polymer strands, and the pores are filled with solvent molecules. By heating and addition of solvent the frameworks can be reversibly converted into each other in the solid state, changing the optoelectrical properties. The compounds are thermodynamically analyzed by differential scanning calorimetry. Also, the electrical conductance was proven in a preliminary experiment on a thin crystalline film of 4.

A variety of fluoroarene-2-aminopyrimidine (FAP) silver(I) coordination polymers (CPs) has been synthesized based on newly synthesized FAP derivatives, namely 5-(p-methoxytetrafluorophenyl)-2aminopyrimidine (OFAP) and 5-(p-dimethylaminotetrafluorophenyl)-2-aminopyrimidine (NFAP), and different counterions (OTf 2 , TFA 2 , ClO 4 2 , NO 3 2). Their solid-state assembly as well as optical properties in terms of luminescence and infrared (IR) spectroscopy were investigated. Out of the several structures described herein, we obtained isomorphic CPs to previous studies (5, 9), a CP architecture with a short Ag-Ag distance (8, 3.049 Å), but also polymorphic crystals of [Ag(nfap)NO 3 ] n (11a, 11b) and the latter showed differences in color and luminescence emission. Polymorphism gives an unparalleled possibility to investigate the origin of such phenomena since luminescence emission is quite often observed for these silver-hybrid solid-state materials and in several cases Ag … Ag interactions are attributed for this phenomenon. We show that this explanation does not necessarily have to be the only one. Therefore we focus also on structural relationships and differences in a comprehensive comparison of our own and other known systems to start a more systematic description of the rich coordination capabilities of FAP and congeneric 2-aminopyrimidine (2-AP) based silver(I) coordination polymers and networks. Density functional theory (DFT) calculations with periodic boundary conditions based on a plane wave basis are used to better understand the electronic structure of these crystalline materials. To complete the picture, steady-state spectroscopy studies (UV-Vis, fluorescence, IR) on all ligands and 2-AP itself were conducted as well as re-examination of the first reported CP of 2-AP and Ag I under the above aspects.

In this work, the exothermic reaction of the chemical energy storage material for stranded renewable energy, lithium is analyzed in carbon dioxide (CO2) and air. Spectroscopic techniques were used to characterize the reaction of bulk lithium pellets of up to 1 g weight. In comparison, power plant applicable combustion of atomized lithium spray was analyzed.Electrical high voltage spark was used to overcome to activation energy of the combustion for the experiments with bulk lithium. The lithium spray was successfully ignited by pre-heating the reaction gases (air and CO2).Radiation temperature of the bulk lithium during reaction in air was calculated to 2260 K. The observed green and red emission of the lithium combustion could be demonstrated in the spectral analysis.In CO2 atmosphere the reaction products were found to be lithium carbonate with little lithium oxide. Beside, lithium carbide could be detected in the reaction product of the combustion of bulk lithium. The gaseous reaction product carbon monoxide (CO), which could be further converted with hydrogen from renewable sources to valuable methanol or gasoline, was detected online by gas analysis.

Femtosecond (<300fs fwhm) measurements of fluorescence decay and quenching of Tryptophan (Trp) were performed in a variety of proteins, including GB1, Thioredoxin (both wild type from two species and a human Trx mutant with a single Trp), Cyanovirin and Interleukin-1beta using an upconversion spectrophotofluorometer combined with a time correlated single photon counting apparatus to span the ~200fs to 20ns time scale. Trp is subject both to ultrafast quenching in proteins and spectral energy loss coupled to nearby water dynamics. All fluorescence transients of tryptophan in proteins reveal complex, i.e. multiexponential behavior. In addition to a ''bulk water'' relaxation (~2 ps), a 50 ps fluorescence decay was found in single-Trp thioredoxin which matched the component we had found previously in two-Trp Anabaena and E. coli thioredoxins . In fact, a sub-100ps component is consistently found in all but one of these proteins with positive amplitudes even at longer wavelengths (e.g., 390nm). The exception is GB1, a protein which Toptygin and Brand previously found carried a negative preexponential term near 390nm. Since the lifetime associated with that negative was 65ps, it was just within the edge of TCSPC detection. The more prevalent positive amplitude DAS (decay-associated spectra) we see in the other proteins on these timescales are indicative of ultrafast quenching processes depleting the partly relaxed singlet state. Candidate mechanisms include ET to nearby acceptors and/or collisional quenching. This is similar to our prior observation (J. Am. Chem. Soc., 2006, 128, 1214) that ultrafast quenching, not desorbing water, dominates the time-resolved emission spectra (TRES) of monellin. We will discuss the À/þ data signatures for both water relaxation and fast quenching, including simulations to lay out the circumstances where a fast relaxation accompanied by a direct radiative rate reduction might mask the negative term.