On the ambiguity of 1,3,2-benzodiazaboroles as donor/acceptor functionalities in luminescent molecules

A series of 1,3-bis(perfluoroaryl)-2-(hetero)aryl-1,3,2-benzodiazaboroles, 1,3-FAr2-2-Ar-1,3,2-N2BC6H4 (Ar = Ph, FAr = C6F5 5; Ar = Ph, FAr = 4-C5F4N 6; Ar = Ph, FAr = 4-NCC6F4 7; Ar = 2-C4H3S, FAr = C6F5 8; Ar = 2-C4H3S, FAr = 4-C5F4N 9; Ar = 2-C4H3S, FAr = 4-NCC6F4 10), were synthesised by cyclocondensation of the adducts PhBBr2·PPh3 or 2-thienylBBr2·PPh3 with N,N′-bis(perfluoroaryl)-o-phenylenediamines in the presence of 2,2,6,6-tetramethylpiperidine. Similar treatments of the PPh3 adducts of 4-(1′,3′-diethyl-1′,3′,2′-benzodiazaborolyl)-phenyldibromoborane with the corresponding diamines gave rise to the push–pull compounds, C6H4(NEt)2B-1,4-C6H4-B(NFAr)2C6H4 (FAr = C6F5 11; 4-C5F4N 12) and C6H4(NEt)2B-2,5-C4H2S-B(NFAr)2C6H4 (FAr = C6F5 13; 4-C5F4N 14). The X-ray structures of 8, 11, 12 and 13 were determined. Electronic structure calculations reveal that the LUMOs are located at the perfluoroaryl groups in 5–14; thus the fluorinated benzodiazaborolyl groups are considered as electron-withdrawing moieties. These moieties differ from alkylated benzodiazaborolyl groups which are regarded as donors. The emission spectra for 5–14 show charge transfer bands with significant solvatochromism and large Stokes shifts (6100–12500 cm−1 in cyclohexane and 8900–15900 cm−1 in CH2Cl2). The emissions of the benzodiazaboroles, 5–10, arise from a different charge transfer (CT) process to the local charge transfer (LCT) process typically found in many fluorescent benzodiazaboroles. This novel remote charge transfer (RCT) process involving the perfluoroaryl groups is supported by CAM-B3LYP computations. The push–pull systems 11–14 here give fluorescent emissions with moderate to high fluorescence quantum yields (65–97%) that arise from the usual LCT process only

Analyse der zeitlichen und örtlichen Struktur turbulenter Verbrennungsprozesse mit Hilfe laserspektroskopischer Verfahren

Brockhinke A. Analyse der zeitlichen und örtlichen Struktur turbulenter Verbrennungsprozesse mit Hilfe laserspektroskopischer Verfahren. Göttingen: Cuvillier; 1996

Investigation Of Excited-State Relaxation In Single-Tryptophan-And Other Proteins Via Multidimensional Static And Time-Resolved Fluorescence

Schwedler S, Kohse-Höinghaus K, Brockhinke R, Brockhinke A. Investigation Of Excited-State Relaxation In Single-Tryptophan-And Other Proteins Via Multidimensional Static And Time-Resolved Fluorescence. In: Biophysical Journal. Vol 96. Elsevier BV; 2009

Energy transfer in combustion diagnostics: Experiment and modeling

Brockhinke A, Kohse-Höinghaus K. Energy transfer in combustion diagnostics: Experiment and modeling. FARADAY DISCUSSIONS. 2001;119(1):275-286.Laser induced fluorescence (LIF) of OH (A (2)Sigma (+)) is measured in several atmospheric-pressure flames using a short-pulse laser system (80 ps duration) in conjunction with an intensified streak camera. The two-dimensional signal-detection technique allows one to simultaneously monitor rotational and vibrational relaxation as well as electronic quenching. Rotationally-resolved LIF spectra affected by energy transfer are compared with the results of a rate-equation model and are found to be in reasonably good agreement. It is shown that a significant contribution of fluorescence detected by broad-band techniques is due to levels populated by vibrational energy transfer (VET). Implications for picosecond LIF techniques for the time-resolved, quench-free detection of OH are discussed. A detailed analysis is presented for fluorescence spectra originating from levels populated by VET after excitation of states in the OH (A (2)Sigma (+), v' = 2) level

Rotationally resolved single-photon ionization of HCl and DCl

Drescher M, Brockhinke A, Böwering N, Heinzmann U, Lefebvre-Brion H. Rotationally resolved single-photon ionization of HCl and DCl. Journal of Chemical Physics. 1993;99(4):2300-2306

Solvatochromism and fluoride sensing of thienyl-containing benzodiazaboroles

Schwedler S, Eickhoff D, Brockhinke R, Cherian D, Weber L, Brockhinke A. Solvatochromism and fluoride sensing of thienyl-containing benzodiazaboroles. Physical Chemistry Chemical Physics. 2011;13(20):9301-9310.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

Selected papers about chemiluminescence of flames

Brockhinke A, Schulz C. Selected papers about chemiluminescence of flames. Applied Physics B. 2012;107(3):513-514

Zuschauen bei der chemischen Reaktion: Detektivarbeit mit Lasern und Massenspektrometern

Kohse-Höinghaus K, Brockhinke A. Zuschauen bei der chemischen Reaktion: Detektivarbeit mit Lasern und Massenspektrometern. Nordrhein-Westfälische Akademie der Wissenschaften und der Künste, Vorträge. N, Naturwissenschaften und Medizin. Vol 474. Paderborn: Ferdinand Schöningh; 2009