dc.description.abstract | In this thesis, we report the design and synthesis of two ICT-based intrinsic fluoroionophore series of trans-4- aminostilbenes (1B and 2B). The 1,2-difluor-/fluoroionophoric behavior of the benzo-12-crown-4- (B12C4) and benzo-15-crown-5- (B15C5) and benzo-18-crown-6- (B18C6) -derived species (1B4-1B6 and 2B4-2B6) in acetonitrile and dichloromethane are also investigated. Great similarities in electronic spectroscopic properties (chemical shifts, wavelength, intensity, and lifetime) between the metal ion-complexed supermolecules and the corresponding 1,2-difluor-substituted molecules have been observed: namely, 1B5/ⅡA and 2B5/ⅡA~1DF and 2DF in acetonitrile and 1B4/ⅠA -1B6/ⅠA ~ 2B4/ⅠA -2B6/ⅠA ~ 1B6/ⅡA- 2B6/ⅡA ~ 1DF and 2DF in dichloromethane. Such spectroscopic correlations allow us to define the metal ion-modulated electronic character of the benzocrown oxygen atom in the ground and excited states and, in turn, to gain insights into the observed fluoroionophoric behavior of these probes in terms of the size and direction of fluorescence shifts and intensity variations.
Amino-based fluoroionophores 3B5 and 4B5 can selectively sense alkaline earth metal ions in MeCN under both neutral and acidic conditions by different signaling mechanisms. The fluoroionophoric behavior for the neutral probes is characterized by an ‘off–on’ photoinduced electron transfer (PET)-like fluorescence intensity response due to a switching from a twisted internal charge transfer (TICT) to a planar internal charge transfer (PICT) state. For the protonated probes (i.e., 3B5/H+ and 4B5/H+), the fluorescing species is the localized stilbene fluorophores, but dual fluorescence is induced upon metal-ion recognition through a deprotonation process.
Two compound series of trans-4-aminostilbenes DS and DCS (D-A and D-only substituted) to gain further insight into solvent effects on the photoisomerization, the temperature-dependent fluorescence lifetimes in methylcyclohexane and in acetonitrile were determined. The introduction of N-phenyl substituents to 4-aminostilbenes leads to a more stable the 1t*-state and reduced torsion barrier (Ea) in polar solvent. Although, the 1t*-state does not like 1p*-state not to be able accurately to describe, but there the molecular polarity are showen that just compared the Ea values with polar solvent and nonpolar solvent. | en_US |