SENSITIZED NEAR-INFRARED EMISSION FROM ND3-BEARING CALIX[4]ARENE CAGES( AND ER3+ COMPLEXES OF FLUORESCEIN)

Three novel, fluorescein-containing calix[4]arenes bearing three carbo xylic acid or three diethylamide functions were synthesized for the co mplexation of Nd3+ or Er3+. The typical Nd3+ luminescence in the near- infrared region of the electromagnetic spectrum is increased up to sev en times upon excitation via fluorescein relative to calix[4]arene exc itation. The calix[4]arene moiety itself already acts as a sensitizer; however, fluorescein is not only a more efficient sensitizer, but als o makes excitation in the visible part of the electromagnetic spectrum (at approximately 500 nm) possible. In contrast, Er3+ luminescence co uld only be observed upon fluorescein excitation. The luminescence int ensity is strongly dependent on the conformational properties of the l igand, the solvent, and the length of the spacer between the calix[4]a rene and fluorescein, The luminescence lifetimes are solvent-dependent but independent of the length of the flexible spacer between the sens itizer and the calix[4]arene. They were determined as 1.23-1.26 mu s f or calix[4]arene complex 1.Nd3+ and 1.63-1.71 mu s for 1.Er3+ in DMSO solutions.