Anionic Hydrogen‐Bonded Frameworks Showing Tautomerism and Colorful Luminescence for the Ultrasensitive Detection of Acetone

Abstract

Tautomers coexisting in an equilibrium system have significant potential in regulating luminescent properties due to their structural differences. However, separating and stabilizing tautomers at room temperature is a considerable challenge. In this work, it is found that hydrogen‐bonded organic frameworks (HOFs) composed of Br‐ anionic can effectively separate and stabilize two proton‐transfer tautomers of triarylformamidinium bromide: nitrogen cation (BA‐N) and carbon cation (BA‐C). BA‐N crystal with dense anionic HOF and parallelly aligning organic cations exhibits green thermal activation delayed fluorescence and red room‐temperature phosphorescence (RTP). BA‐C crystal contains acetone molecules that induce antiparallel arrangement of organic cations to form loose HOF, producing blue prompt fluorescence and green RTP. Interestingly, the HOFs switching between BA‐N and BA‐C can be achieved through the inhalation and exhalation of acetone, thereby dynamically adjusting multiple luminescent behaviors. Consequently, the HOF crystals can be used in highly sensitive and specific acetone sensing with a detection limit of 66.74 ppm. This work not only stabilizes tautomeric luminescent materials at room temperature, but also provides a new method for constructing smart HOFs with sensitive stimulus response.

Flexible hydrogen-bonded organic frameworks (HOFs): opportunities and challenges

“…). 59–69 Or, sometimes, the H-bonding patterns will just be reorganized without losing the framework crystallinity, thus leading to a structural transformation. For example, the ethanol-bridged carboxyl dimers in HOF-30 reported by Wang et al have exhibited reversible structural transformations with the removal of ethanol during the activation process or soaking in the solvent again.…”

“…As a multifunctional luminescent framework material with both luminescent and porosity properties, it has a broad application prospect in the field of sensing. 63,68,72,94–102…”

“…A novel triaryl formamidine salt containing two isomers (BA-C and BA-N) was reported by Lin et al 68 These two isomers can be recrystallized in different solvents to form two different HOFs, and it was found that the removal of acetone from the lattice of BA-C by grinding or heating could lead to the conversion of BA-C to BA-N, and in turn, exposing to acetone vapor or cooling at 77 K could lead to the conversion of BA-N to BA-C, thus realizing the reversibility of the conversion of BA-N and BA-C, and showing the flexibility of these HOFs ( Fig. 16 ).…”