Vapochromic Platinum(II) Complexes: Crystal Engineering toward Intelligent Sensing Devices

Abstract

Vapochromic materials that show reversible color change driven by vapor adsorption/desorption have drawn significant attention because of their potential applications in chemical sensors and chemical‐switching modules. Among the vapochromic coordination complexes reported so far, a series of square‐planar PtII complexes has been studied and represents one of the most promising systems for practical chemical sensors. For such systems, the color of the complexes strongly depends not only on the ligand‐field splitting, but also on the intermolecular distance between the PtII ions. This microreview presents recent results of vapochromic complexes centered on one‐dimensionally stacked PtII systems from the viewpoint of the origin of their vapochromic behavior. The design of vapochromic materials has been facilitated because several useful chromophores, including metallophilic interaction between PtII ions, have been developed. However, it is still challenging to realize a specifically sensitive and selective response to targeted vapors. This review focuses on strategies to achieve assembled PtII complexes with selective vapochromic responses.

Supramolecular Phosphorescent Trinuclear Copper(I) Pyrazolate Complexes for Vapochromic Chemosensors of Ethanol

“…Therefore, these phenomena suggest that the molecular structure of chemosensors with a short alkyl side chain at the pyrazole ring of the complexes gave significant effect on the sensing capability with quenching phenomena toward the ethanol vapors. Since molecular size of ethanol is not large enough to cut-off the metal-metal interaction among pyrazolate molecules, such changes in emission spectra [3][4][5][12][13][14][15][16][17][18][19][20] and colors [4,12,35] in quenching phenomenon might be caused by the formation of a weak intermolecular hydrogen bonding interaction [4,13,[18][19][20][25][26][27]35] from OH of ethanol vapors with electronegative N and/or F atoms at the pyrazole ring so that the metal-metal interaction was totally disrupted and cannot form a bonding between the molecules. In the presence of bulky side chains from -CH 3 , the sensing capability will be reduced due to the influence of accessibility of ethanol vapors from that bulky group to be diffused to the emission center.…”

“…Since phosphorescent compounds are indicated by its longer luminescent lifetime from the metal-metal interactions than the fluorescence, many complexes from d 6 , d 8 and d 10 metal ions with extended π-system or coordination donors have been synthesized as phosphorescent metal complexes. The resulting metal complexes have revealed color changes from vapor-triggered luminescence owing to metal-solvent, metal-metal, π-π, hydrogen bonding and host-guest interactions [12]. In this case, supramolecular phosphorescent metal complexes with their self-assembling properties have been extensively explored as chemosensors due to possibility of changes in tunability and rigidity [13][14].…”

Recent Advances in Phosphorescent Pt(II) Complexes Featuring Metallophilic Interactions: Properties and Applications

“…the stimulus and the material property subject to change, determine the field of application of the responsive material. Pt complexes have been found to change either (or both) absorption and emission colors as a result of a variety of stimuli, including vapors of volatile organic compounds (VOCs) as recently reviewed by Wenger 65 and Kato, 25 as well as mechanical stresses such as grinding, scraping, or compression. 66 Both absorption and emission colors are excellent signal candidates for sensing applications, since the sensitivity of human eye and of common charge-coupled device (CCD) sensors allows for implementation of fast tests performed by individual, nontrained persons, or by low-cost automated sensors such as smartphone or industrial cameras.…”

Supramolecular assembly of group 11 phosphorescent metal complexes for chemosensors of alcohol derivatives

“…In particular, phosphorescent d 6 , d 8 and d 10 metal compounds with extended π or coordination donor systems have been widely developed as vapochromic chemosensors with several advantages from their photophysical properties such as sensitivity of emission, Stokes shifts, excitation of single photon and longer lifetime [4][5][6]. Considering luminescent changes such as shifting, quenching, positive response and photoinduced energy transfer, phosphorescent metal complexes have shown great attention as vapochromic chemosensors with high tunability and rigidity of supramolecular metal-solvent, metal- metal, π-π, hydrogen bonding and host-guest interactions [4,[7][8][9]. For example, Nagel and co-workers in 1988 [10] synthesized palladium (Pd) and platinum (Pt) double-complex or mixed salt for the detection of vapors.…”