Calcium Photorelease from a Symmetrical Donor−Acceptor−Donor Bis-crown-fluoroionophore Evidenced by Ultrafast Absorption Spectroscopy

The excited-state properties of a calcium dicomplex (AM 2 ) of 2,5-[bis-[4 N -(aza-15-crown-5)phenyl]methylene]cyclopentanone ( A ) in acetonitrile are investigated by ultrafast absorption spectroscopy. Spectroscopic evidence of an ultrafast cation decoordination following subpicosecond excitation of the chromophore is given. A global analysis of the time-resolved data is performed, and a kinetic scheme is tentatively proposed, which quantitatively describes the dynamics of the deactivation pathway of the AM 2 dicomplex. A first step would involve the disruption of one of the two nitrogen−calcium bonds at a rate constant of 4 × 10 11 s -1, followed by the diffusion of the cation out of the crown at a rate of 5.8 × 10 10 s -1 . The resulting AM complex would then relax both to its ground state (5.4 × 10 8 s -1 ) and to its triplet state (2.8 × 10 8 s -1 ).