Photophysical study on the sequential ion interaction of an organic receptor: optical detection and advanced multifunctional logic applications

Abstract

In the literature, merely a handful of works report the simultaneous and tandem detection of metal ions, specifically in dual mode through a single molecular platform. The sequential dual chemosensory responses of a new chemosensor, 2-((2-(diethylamino)ethylamino)methyl)-6-methoxyphenol (MDAMP), were confirmed with Zn²⁺ followed by Cu²⁺ ions. Interestingly, the probe contains an aliphatic chain as an electron donor moiety and an aromatic end as an acceptor moiety and undergoes an intrinsic photo-induced electron transfer (PET). Remarkably, MDAMP displays a newly significant absorption band at 450 nm, in presence of exclusively Cu²⁺ ions, accompanied by a noticeable naked-eye color change (colorless to brown), but remains unaltered in the presence of Zn²⁺ ions. Notably, the fluorescence intensity of the poorly emissive probe remains unaltered in the presence of Cu²⁺ ions but is promoted remarkably in the presence of Zn²⁺ with a redshift in emission maxima. However, in the presence of Cu²⁺ ions, the emission intensity of the MDAMP–Zn²⁺ composite dramatically declined. The Zn²⁺-induced emission enhancement of MDAMP might have resulted from chelation-enhanced fluorescence (CHEF), with concurrent inhibition of the intrinsic PET. Moreover, the experimentally obtained photophysical changes in MDAMP were also thoroughly investigated through extensive DFT calculations. Further, the precise spectroscopic responses have been utilized in the decoration of multifunctional opto-chemical logic functions (YES, NOT, AND, INHIBIT, PASS 0, PASS 1, TRANSFER and TERNARY/QUATERNARY combinational gates), which remain inherently valuable in the digital era.