Strategic Design of Non-d¹⁰ Luminescent Metal–Organic Frameworks as Dual-Mode Ultrafast and Selective Sensing Platforms for Aldehydes at the ppb Level

Abstract

Utilizing a cautious design of luminescent MOFs of non-d 10 divalent transition metals based on two factors (metal nodes in an octahedral geometry to minimize nonradiative energy dissipation and tailored organic chromophores), this work reports {[Ni 2 (oxdz) 2 (tpbn)]} n (1), {[Ni 2 (oxdz) 2 (tphn)]} n (2), and {[Ni 2 (oxdz) 2 (tpon)]} n (3), synthesized at room temperature, varying the spacer length of tpbn/tphn/tpon (four, six, and eight CH 2 groups, respectively). This subtle change in 1−3 is correlated to their hydrophobicity and polarizing power via water vapor sorption and selective and sensitive detection of aldehydes at the ppb level, respectively. A decrease in water vapor uptake (14.8, 8.95, and 3.19 mmol g −1 for 1−3, respectively) is observed with an increase in their hydrophobicity. On the other hand, the solution phase detection limits of acetaldehyde and benzaldehyde (2.42 and 6.71 ppb for 1, 2.77 and 4.08 ppb for 2, and 10.35 and 10.4 ppb for 3, respectively) show a similar trend for their polarizing power. The best performance of 1 is expanded to the vapor-phase detection of acetaldehyde (297% luminescence enhancement) under different pH conditions. The second mode of detection of acetaldehyde via the metal-centered electrochemical behavior of 1 provides detection limits of 38.2 and 71.5 ppb at pH 7 and 13, respectively.