Zinc sensing via enhancement of two-photon excited fluorescence

A branched chromophore tris[p-(4-pyridylethynyl)phenyl]amine (TPPA) with pyridine terminal groups is investigated for its ability to sense small quantities of Zinc ions via a two-photon excited fluorescence (TPEF) enhancement mechanism. Changes in the linear and nonlinear optical properties upon coordination with Zn2+ have been studied using steady-state measurements, Two-photon absorption and femtosecond transient absorption spectroscopy. An order of magnitude increase in the TPEF signal of the Zn-bound chromophore was observed, thereby rendering our chromophore a turn-on sensor for Zn2+. The molecule was highly selective toward Zn2+ and was able to detect Zn2+ at the ppm level. Transient absorption measurements revealed the excited-state dynamics and elucidated the reasons for the observed behavior of the TPPA chromophore. This study provides a guideline along which organic chromophores could be developed for turn-on metal ion sensing using multiphoton excitation.