Design and characterization of pH-sensitive spirorhodamine 6G probes with aliphatic substituents

DI PAOLO, MATÍAS; BOUBETA, FERNANDO M.; ALDAY, JULIETA; MICHEL TORINO, MATEO; ARAMENDÍA, PEDRO F.; SUAREZ, SEBASTIAN A.; BOSSI, MARIANO L.

JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY

ELSEVIER SCIENCE SA

Año: 2019 vol. 384

1010-6030

We report synthesis and photophysical studies of spirorhodamines (SRA) with amide N-aliphatic substituents,including measurements of single-crystal X-ray structures, fluorescence emission, and quantum mechanicalcalculations. Variations in the equilibrium position between closed and open states, a transition that is catalysedunder acidic conditions, of several SRAs sharing the same central chromophore (Rhodamine 6G) were measured.For the different substituents in the lactam position, the pH-dependent lactam ring opening reaction displays astrong correlation with the volume of the functional group. The open form shows similar absorption andemission spectrum, fluorescence efficiency and emission lifetime, regardless of the nature of the substituents.The molecular volume of the substituent is a simple and straightforward molecular design feature to control theequilibrium between the ?dark? and ?bright? states of the probe, without any further changes in the emissionproperties of the fluorescent form. These results allow rational design of pH-sensitive aliphatic SRAs fluorescentprobes.