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Keywords:

dipyrrometheneboron difluoride bodipy, intramolecular charge-transfer, electron-transfer reactions, boron-dipyrromethene, excited-state, photophysical properties, lasing properties, liquid solution, fluoroionophore, spectra, Science & Technology, Physical Sciences, Chemistry, Physical, Physics, Atomic, Molecular & Chemical, Chemistry, Physics, DIPYRROMETHENEBORON DIFLUORIDE BODIPY, INTRAMOLECULAR CHARGE-TRANSFER, ELECTRON-TRANSFER REACTIONS, BORON-DIPYRROMETHENE, EXCITED-STATE, PHOTOPHYSICAL PROPERTIES, LASING PROPERTIES, LIQUID SOLUTION, FLUOROIONOPHORE, SPECTRA, 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics, 0306 Physical Chemistry (incl. Structural), 0307 Theoretical and Computational Chemistry, 3406 Physical chemistry, 3407 Theoretical and computational chemistry, 5102 Atomic, molecular and optical physics

Abstract:

Steady-state and time-resolved fluorescence techniques have been used to study the photophysical properties of the fluorescent BODIPY-derived dye 3-{2-[4-(dimethylamino) phenyl] ethenyl}-4,4-difluoro-8-( 4- methoxyphenyl)1,5,7-trimethyl-3a, 4a-diaza-4-bora-s-indacene. This compound has been synthesized via a microwave-assisted condensation of p-N,N-dimethylaminobenzaldehyde with the appropriate 1,3,5,7-tetramethyl substituted borondipyrromethene unit. The fluorescence properties of the dye are strongly solvent dependent: increasing the solvent polarity leads to lower fluorescence quantum yields and lifetimes, and the wavelength of maximum fluorescence emission shifts to the red. The Catalan solvent scales are found to be the most suitable for describing the solvatochromic shifts of the fluorescence emission. These are dominated by polarity/polarizability effects, as confirmed by quantum-chemical calculations performed in the dielectric continuum approximation. Fluorescence decay profiles of the dye can be described by a single-exponential fit in most solvents investigated, while two decay times are found in alcohols. The dye undergoes a reversible protonation-deprotonation reaction in the acidic pH range with a pKa of 2.25 in acetonitrile solution. Fluorimetric titrations as a function of pH produce fluorescence emission enhancements at lower pH. The fluorescence excitation spectra show a hypsochromic shift from 600 nm for the neutral amine to 553 nm for the ammonium form, so that ratiometric measurements can be used to determine pK(a).