Several Probes Derived from Tetraphenyl Ethene and Triphenylamine for Cu(II) and Intracellular Carbon Monoxide Sensing

Optical detection is a promising method for Cu²⁺ detection with merits, including short sensing times, low cost, sensitive response, and ease of implementation. In this work, tetraphenylethene and triphenylamine were selected as the structural cores for constructing optical probes for Cu²⁺. The tetraphenylethene and triphenylamine groups were bonded to a N-N group, forming a probe structure. Additionally, there were two -OH groups near the N-N group, offering additional recognition sites to improve the sensing selectivity. The discussion covered the geometry, electronic transitions, optophysical properties, and spectroscopic behaviors toward copper-(II). It was concluded that the -OH group improved the sensing selectivity by increasing the affinity between the probe and Cu²⁺. The electron donors in these dyes compromised the sensing selectivity but decreased the emission recovery time. The optimal probe (P1) decreased its emission quantum from 7.8 to 0.2% by Cu²⁺ and then recovered to 7.4% by CO within 529 s, with its emission spectrum well recovered. The emission recovery of P1 was sensitive to temperature, and a high temperature (40 °C) helped P1 emission recovery. The recognition principle was yielding a nonemissive adduct between the probe and Cu²⁺ with a complexation constant of 6.25 × 10⁷ L/mol. The sensing mechanism toward Cu²⁺ was revealed as the combination of static and dynamic sensing with Job's plot, lifetime comparison, ¹H NMR, and IR comparison. The other four probes, having no -OH groups, exhibited poor sensing selectivity and lower emission recovery values. Their emission recovery times were shorter than that of P1 due to the steric factor and electronic structure. The practical sensing and imaging performance of P1 was tested.