Rare Example of TICT Based Optical Responses for the Specific Recognition of Cr³⁺ by a 2,2′:6′,2″-Terpyridine Derivative and Demonstration of Multiple Logic Operations

Abstract

Chemosensor <b>L</b> showed a <i>nonlinear fluorescence</i> response on specific binding to Cr³⁺ ion in the presence of various alkali, alkaline-earth, transition, and lanthanide metal ions. A luminescence band with maxima at 512 nm for <b>L</b> was observed (λ_ext = 330 nm) for a twisted intramolecular charge transfer (TICT) transition following antienergy gap law behavior. However, normal energy gap law behavior prevailed on formation of a new nonluminescent charge transfer complex, M^<i>n</i>+·<b>L</b>. For paramagnetic metal ions, paramagnetism induced luminescence quenching could have also contributed to this. A new <i>switched on</i> fluorescence response at λ_ems of 356 nm (λ_ext of 330 nm) was observed due to Franck–Condon charge transfer (FC-CT) transition only on the formation of a complex, (Cr³⁺)₂·<b>L</b>. Spectral studies revealed a unique dynamic coordination behavior and migration of Cr³⁺ from the terpyridyl fragment to the N_NMe₂ center of <b>L</b> as a function of the varying concentration of another ion (Zn²⁺) and the subtle difference in the binding affinities of the terpyridyl moiety toward Cr³⁺ and Zn²⁺. Further, spectral responses of <b>L</b> toward Zn²⁺, different concentration of Cr³⁺, H⁺ and on subsequent addition of F^– as different ionic inputs could be correlated well for demonstrating various basic and combinatorial circuits