Matthias Kollmannsberger

Molecular Switching in the Near Infrared (NIR) with a Functionalized Boron–Dipyrromethene Dye

The highly fluorescent, unsymmetrically substituted boron-dipyrromethene dye 1 shows emission features that are strongly dependent on the solvent polarity. Thus, 1 can be used for highly sensitive fluorometric probing of solvent polarity and acidity and furthermore can be switched chemically or electrochemically in the near infrared.

A highly efficient sensor molecule emitting in the near infrared (NIR): 3,5-distyryl-8-(p-dimethylaminophenyl)difluoroboradiaza-s-indacene

The spectroscopic properties and the photophysical behaviour of difluoroboradiaza-s-indacene 1, especially designed for the near infrared (NIR) spectral region and equipped with a p-dimethylaminophenyl group at the meso-position, were studied by steady-state and time-resolved optical spectroscopy. Solvent-dependent measurements revealed that for 1, excited state deactivation is governed by population of a non-emissive charge transfer excited state (1CT) as the solvent polarity increases, whereas reference compound 2 shows strong fluorescence from a locally excited state (1LE) in all the solvents employed. Accordingly, protonation of 1 completely suppresses the quenching excited state charge transfer process and leads to strong enhancement of fluorescence in the NIR, distinguishing 1 as a very sensitive fluorescent sensor molecule for pH or solvent acidity in this favourable wavelength region.

Design of an efficient charge-transfer processing molecular system containing a weak electron donor: spectroscopic and redox properties and cation-induced fluorescence enhancement

Abstract The acceptor strength of the boron-dipyrromethene chromophore in directly linked donor–acceptor compounds can be tuned by substituents in such a way that a fast excited state charge transfer takes place even for the comparatively weak benzo crown electron donor. This leads to strong fluorescence quenching. Upon binding of cations (Na + and K + ) to the benzo crown receptor, the donor properties of the latter are further reduced, partly suppressing charge transfer. Large fluorescence enhancement factors and cation-selective fluorescence decay times result which are the basis for improved analytical application of these dyes as highly sensitive fluorescent probes.