A Cobalt(II) based coordination architecture for efficient colorimetric sensing of ammonia and amine vapors

Abstract

This work presents the design, synthesis, and characterization of a new cobalt (II) based coordination architecture, {[Co(toua)(4,4′-bpy)].2H2O}n (1); where toua is 3,6,9-trioxaundecanaote and 4,4′-bpy is 4,4′-bipyridine tailored for efficient sensing of ammonia and amines. The formation and identity of 1 was confirmed by elemental analysis, spectroscopic study (FTIR and UV–visible spectroscopy), PXRD, XPS, FESEM, and BET analysis. The colorimetric sensing capability of 1 towards ammonia and various smaller-sized amines in the vapor phase through observable color changes is explored in this study. Their interaction with 1 is elucidated through FTIR, UV–Visible and Fluorescence spectroscopy, FESEM, and TCSPC analysis. The fluorescence sensing experiments demonstrate a remarkable quenching/enhancement effect with the addition of ammonia and various amines, showcasing the compound’s sensitivity and selectivity. The quenching/enhancement efficiency follows the order: NH3>Ethylenediamine (EDA)>1,3-diaminopropane (DAP)>n-propylethylenediamine (n-PEDA), following the molecular dimensions and steric hindrance surrounding nitrogen atoms. Hydrogen bonds and host-guest interactions, including (C–H)pyridinium⋅⋅⋅N interactions, are identified as the driving forces for the sensing process. Additionally, the paper reveals a rare occurrence of both “turn-off” and “turn-on” sensing behavior for the same compound, showcasing its versatility. The calculated RSD for the fluorometric sensor was found to be 1.03 % calculated from its triplicate readings at 240 nm. Limits of detection (LODs) and Limit of Quantification (LOQs) for NH3 (0.52 μM, and 1.74 μM) EDA (1.2 μM, and 4.2 μM), DAP (3.1 μM, and 10.5 μM), and n-PEDA (3.3 μM, and 11.2 μM) respectively) underscore the effective sensing capabilities of 1. The robustness of 1 upon exposure to amines was confirmed by PXRD. These findings justify that 1 is a promising vaporchromic probe for the fast and selective detection of ammonia and amines.