| Abstract
| - Steady-state and time-resolved fluorescence techniques have been used to study the photophysical propertiesof 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 substitutedborondipyrromethene unit. The fluorescence properties of the dye are strongly solvent dependent: increasingthe solvent polarity leads to lower fluorescence quantum yields and lifetimes, and the wavelength of maximumfluorescence emission shifts to the red. The Catalán solvent scales are found to be the most suitable fordescribing the solvatochromic shifts of the fluorescence emission. These are dominated by polarity/polarizabilityeffects, 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−deprotonationreaction in the acidic pH range with a pKa of 2.25 in acetonitrile solution. Fluorimetric titrations as a functionof pH produce fluorescence emission enhancements at lower pH. The fluorescence excitation spectra showa hypsochromic shift from 600 nm for the neutral amine to 553 nm for the ammonium form, so that ratiometricmeasurements can be used to determine pKa.
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