Photophysical Properties of the Pyrromethene 597 Dye: Solvent Effect

UV−vis absorption spectroscopy and fluorescence (steady-state and time-resolved) techniques were used to study the photophysical properties of the pyrromethene 597 (PM597) dye in several solvents, which include a wide range of apolar, polar, and protic media. This dye presents a lower fluorescence quantum yield than the well-known PM567 dye because of an increase in the nonradiative deactivation rate constant. This is attributed to a loss of planarity in the excited state provided by the steric hindrance of the tert-butyl groups at positions 2 and 6 of the chromophore core. Such a geometrical change in the excited state leads to an important Stokes shift, reducing the reabsorption and reemission effects in the detected emission in highly concentrated dye solutions. The highest fluorescence quantum yield of PM597 is observed in polar media.