RESUMO
The fluorescent properties of a recently synthesized photochromic naphthopyran containing a 1-aza-15-crown-5 moiety (1b) and its crownless analogue (1a) were studied. 1b emits fluorescence with a maximum at 528 nm, quantum yield 0.1 and characteristic lifetime 2.4 ns (in acetonitrile at room temperature). Its luminescence could be switched off photochemically in two ways using two parallel photochemical reactions characteristic for this type of naphthopyran. The first way is the irreversible transcis photoisomerization of a closed form ("stilbene-like reaction"). The second way is the thermally reversible reaction of closed form transition to the open form ("chromene-like reaction"). The fluorescence of 1b is quenched by alkali earth metal cations by the mechanism of static quenching. Stability constants for 1 : 1 complexes of 1b with Mg(2+) and Ba(2+) determined from Stern-Volmer plots are in agreement with that obtained by UV spectroscopy.
RESUMO
A macrocyclic benzo-15-crown-5 ether unit tethered to a photochromic naphthopyran by a styryl spacer (MEN) is shown to form a 1:1 complex with magnesium(II). The structure and dynamics of the specific host-metal interactions were investigated by PFG-NMR analysis. A combination of UV/Vis and variable temperature multi-dimensional (1)H NMR photokinetic analysis of the crown-containing styryl naphthopyran and its metal complex was used to probe the effect of metal complexation on the photochromism.
RESUMO
The photochromic properties of a chromene derivative, which contains a positively charged substituent, were investigated in the presence of ct DNA. Upon irradiation in the absence of DNA the colored quinoid open form is highly unstable and rapidly reverts back to the initial closed form (bleaching). In the presence of DNA the open form is significantly stabilized, presumably because of the association with the macromolecule. The kinetics of the bleaching reaction of the bound ligand were determined and employed to estimate the binding constant.