New ferrocenyl naphthoquinone fused crown ether chemosensors: Highly selective, kinetically and regio controlled colorimetric, beryllium ion recognition

Abstract

New organometallic chemosensors which are based on triad molecules, ferrocenyl naphthoquinone linearly/angularly fused crown ethers (Fc-cnq-1a and Fc-cnq-1b) bearing ferrocene, quinone, and crown ether functional groups together, were synthesized and utilized for selective sensing trace amount of Be2+ ion (5.41 mu M) among other metal cations. the UV-vis spectrophotometric titration experiments at controlled temperatures (25-60 degrees C) resulted in characteristic spectral changes in the intramolecular charge-transfer (CT) transitions upon addition of Be2+ ion into the solution of sensors Fc-cnq-1a and Fc-cnq-1b. However, no spectral changes were observed for the other metal cations used for testing at the same conditions, indicating that the sensors can selectively detect Be2+ among the studied metal ions even at higher temperatures. the spectral change in the absorption spectra of the sensors upon addition of Be2+ ion corresponds to the visible region of the spectrum, from deep green to yellow color, and this leads to observe the effect of the Be2+ ion with naked eye. the sensors used for the signaling of Be2+ ion displayed a significant shortening in response time depending on increasing temperature without any degradation of the sensors. Fc-cnq-1a displayed faster response time than Fc-cnq-1b in the temperature range of 35-60 degrees C. the activation energies for the pseudo-first order complexation reactions were calculated as 124.2 +/- 13.0 kJ mol(-1) and 151.9 +/- 18.0 kJ mol(-1) for Fc-cnq-1a and Fc-cnq-1b, respectively, which explains faster response time of Fc-cnq-1a for recognizing Be2+ ion. Density Functional Theory calculations (TD-B97D/TZVP//mPWPW91/6-31 + G(2d,2p) level) were performed on Fc-cnq-1a, Fc-cnq-1b and their Be+2 complexes in order to elucidate their geometries and the molecular orbitals. Calculations have shown comparable results with those obtained from the experimental data. (C) 2018 Elsevier B.V. All rights reserved.