NEW INTRINSIC FLUOROIONOPHORES WITH DUAL FLUORESCENCE - DMABN-CROWN4 AND DMABN-CROWN5

Two new intrinsic fluoroionophores, with the electronic structure of 4 -(dimethylamino)benzonitrile (DMABN): 4-(1-aza-4,7,10-trioxaclyclodode cyl)benzonitrile (DMABN-Crown4) and 4-(1-aza-4,7,10,13-tetraoxacyclope ntadecyl) benzonitrile (DMABN-Crown5) were synthesized and their absor ption, fluorescence spectra and quantum yields of fluorescence measure d and discussed. Comparison of X-ray data and calculations from the de nsity functional theory (DFT) shows that from DMABN to DMABN-Crown5 th e twist angle of the amino group with respect to the phenyl plane incr eases while the pyramidalization of the nitrogen is not significantly affected. The activation energies (E(a) 8.9 kJ . mol(-1), E(d) 23.7 kJ . mol(-1)) and the enthalpy (Delta H-14.8 kJ . mol(-1)) involved betw een the LE and TICT states of DMABN-Crown5 were obtained in toluene an d compared with those previously published for DMABN. The greater reli ef of strain (larger Delta H) which accompanies the formation of the T ICT state in the crown derivatives, accounts for the higher proportion of TICT emission recorded at room temperature. The fluorescence of DM ABN-Crown5 in acetonitrile, is altered significantly at 3 . 10(-4) mol . 1(-1) of Ca2+: the long-wavelength emission from the TICT state dec reases while the short-wavelength emission increases. From the wholly complexed probes, the two emissions are blue-shifted relative to those of the free probe and originate from contact- and/or solvent-separate d probe-cation pair with the probe in the LE and in the TICT state. Si milarly, the fluorescence spectrum of DMABN-Crown4, in acetonitrile, i s altered significantly when Mg(ClO4)(2) is added in concentrations of 5 . 10(-3) mol . 10(-1) or above.