New family of polyamine macrocycles containing 2,5-diphenyl[1,3,4]oxadiazole as a signaling unit. Synthesis, acid-base and spectrophotometric properties.
Synthesis and acid-base properties for three fluorescent polyamine macrocycles 9,12,15,24,25-pentaaza-26-oxatetracyclo[21.2.1.0(2,7).0(17,22)]hexaicosa-2,4,6,17,19,21,23,25(1)-octaene (L1), 9,12,15,18,27,28-hexaaza-29-oxatetracyclo[24.2.1.0(2,7).0(20,25)]enneicosa-2,4,6,20,22,24,26,28(1)-octaene (L2) and 9,12,15,18,21,30,31-heptaaza-32-oxatetracyclo[27.2.1.0(2,7).0(23,28)]diatriconta-2,4,6,23,25,27,29,31(1)-octaene (L3) are reported. Each ligand contains the 2,5-diphenyl[1,3,4]oxadiazole (PPD) unit incorporated in the polyamine macrocycle. The protonation constants of L1-L3 were determined by means of potentiometric measurements in 0.15 mol dm(-3) NaCl aqueous solution at 298.1 K. All the ligands are highly fluorescent in aqueous solution under acidic conditions (pH < 2) and their emission drastically decreases when the pH is increased. At pH > 8, a total quenching of fluorescence is observable in all the ligands. The fluorescence is given by the PPD unit, while the behavior as a function of pH can be rationalized on the basis of photoinduced intramolecular electron transfer (PET) from the HOMO of the donor macrocycle nitrogen atoms to the excited fluorophore unit. The insertion of PPD in a polyamine skeleton strongly improves the fluorescence quantum yield of this class of ligands with respect to those already known.
Ambrosi
Gianluca
G
Institute of Chemical Sciences, University of Urbino, P.zza Rinascimento 6, I-61029, Urbino, Italy.
Formica
Mauro
M
Fusi
Vieri
V
Giorgi
Luca
L
Macedi
Eleonora
E
Micheloni
Mauro
M
Piersanti
Giovanni
G
Pontellini
Roberto
R
D005456:Fluorescent Dyes / Q000138:chemical synthesis / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D047028:Macrocyclic Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D010080:Oxazoles / Q000737:chemistry*; D011073:Polyamines / Q000138:chemical synthesis* / Q000737:chemistry*; D011199:Potentiometry; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet
D005456:Fluorescent Dyes; D047028:Macrocyclic Compounds; D010080:Oxazoles; D011073:Polyamines; C009012:2,5-diphenyloxazole