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

Chemosensor L showed a nonlinear fluorescence 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 L was observed (lambda(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, Mn+center dot L. For paramagnetic metal ions, paramagnetism induced luminescence quenching could have also contributed to this. A new switched on fluorescence response at lambda(ems) of 356 nm (lambda(ext) of 330 nm) was observed due to Franck-Condon charge transfer (FC-CT) transition only on the formation of a complex, (Cr3+)(2)center dot L. Spectral studies revealed a unique dynamic coordination behavior and migration of Cr3+ from the terpyridyl fragment to the N-NMe2 center of L 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 L 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.