Dual Binding Site Assisted Chromogenic and Fluorogenic Recognition and Discrimination of Fluoride and Cyanide by a Peripherally Borylated Metalloporphyrin: Overcoming Anion Interference in Organoboron Based Sensors

Abstract

Peripherally triarylborane decorated porphyrin (2) and its Zn(II) complex (3) have been synthesized. Compound 3 contains of two different Lewis acidic binding sites (Zn(II) and boron center). Unlike all previously known triarylborane based sensors, the optical responses of 3 toward fluoride and cyanide are distinctively different, thus enabling the discrimination of these two interfering anions. Metalloporphyrin 3 shows a multiple channel fluorogenic response toward fluoride and cyanide and also a selective visual colorimetric response toward cyanide. By comparison with model systems and from detailed photophysical studies on 2 and 3, we conclude that the preferential binding of fluoride occurs at the peripheral borane moieties resulting in the cessation of the EET (electronic energy transfer) process from borane to porphyrin core and with negligible negetive cooperative effects. On the other hand, cyanide binding occurs at the Zn(II) core leading to drastic changes in its absorption behavior which can be followed by the naked eye. Such changes are not observed when the boryl substituent is absent (e.g., Zn-TPP and TPP). Compounds 2 and 3 were also found to be capable of extracting fluoride from aqueous medium.

Switchable Optical Probes for Simultaneous Targeting of Multiple Anions

“…[121] Recently, a triarylborane decorated Zn (II)-porphyrin complex (49) has been designed by Thilagar and his group for simultaneous detection of F À and CN À ion. [122] As expected, fluoride ion preferentially bound to the peripheral boron center and faded the original yellow color of the compound, while cyanide mostly coordinated at the electron deficient Zn(II) center and resulted in distinctive green coloration. Yu et al developed a BODIPY-coumarin conjugate (50) for simultaneous detection of CN À and F À in acetonitrile-Tris/HCl (95 : 5) mixture medium.…”

Di‐(2‐picolyl)‐N‐(2‐quinolinylmethyl)amine‐Functionalized Triarylboron: Lewis Acidity Enhancement and Fluorogenic Discrimination Between Fluoride and Cyanide in Aqueous Solution

“…Another point to note is that, in some cases, the typical triarylboranes used in practical fluoride‐sensing applications are influenced by a competing response for cyanide ion . Examples demonstrating that triarylborane‐based sensors can discriminate between fluoride and cyanide in aqueous solution remain exceedingly rare …”

“…[20] Examples demonstrating that triarylborane-based sensors can discriminate between fluoride and cyanide in aqueous solution remainexceedingly rare. [24,25] Tri-(2-picolyl)amine( TPA) is al igand that can bind to av ariety of metal ions with higha ffinity,i ncluding Ni 2 + ,C o 2 + ,C u 2 + , Zn 2 + and Fe 2 + . [26,27] Inspired by the success of cationic boranes, [15] we considered that when combining TPAw ith ArB(Mes 2 ), the pyridyl group of TPAw ould be effective in enhancing the Lewis acidity of at riarylborane due to the electronegative pyridine ring compared to ap henyl group.…”

An OFF–ON–OFF type fluorescent probe based on a naphthalene derivative for Al3+ and F− ions and its biological application

“…It can also lead to changes in blood pressure and even anemia, affecting the growth and development of animals . Hence, there is great need to develop receptors that can combine with and/or detect fluoride in our daily life . The design and application of a single probe that achieves a discriminating response for various analytes, however, has been challenging in recent times …”