Development of luminescent sensors based on transition metal complexes for the detection of nitroexplosives

Abstract

The detection of chemical explosives is a major area of research interest and is essential for the military as well as homeland security to counter the catastrophic effects of global terrorism. In recent years, tremendous effort has been devoted to the development of luminescent materials for the detection of explosives in the vapor, solution, and solid states with a high degree of selectivity and sensitivity and a rapid response time. Apart from the wide range of organic fluorescent chemosensors, transition metal complexes play a prominent role in the sensing of nitroaromatic explosives owing to their rich photophysical characteristics. This review briefly summarizes the salient features of the design and preparation of transition metal (Zn(ii), Ir(iii), Pd(ii), Pt(ii), Re(i) and Ru(ii)) complexes/metallacycles/metallosupramolecules with emphasis on their photophysical properties, sensing behavior, mechanism of action, and the driving forces for detecting explosives and future prospects and challenges. Most of the probes that have been reported to date act as "turn-off" luminescent sensors because their emission (intensity, lifetime, and quantum yield) is eventually quenched upon sensing with nitroaromatic compounds (NACs) through photo-induced electron or energy transfer. These unique properties of transition metal complexes in response to explosives open up new vistas for the development of real world applications such as on-site detection, in-field security, forensic research, etc.

Ligand-controlled and nanoconfinement-boosted luminescence employing Pt(ii) and Pd(ii) complexes: from color-tunable aggregation-enhanced dual emitters towards self-referenced oxygen reporters

“…Transition metal complexes with triplet molecular dioxygen ( 3 O 2 ) -sensitive luminescence at room temperature have been extensively studied in the last decades, due to their broad spectrum of applications, ranging from bioimaging agents [1][2][3][4][5] and photocatalysts 6,7 to active materials in photodynamic therapy, 8,9 OLEDs, [10][11][12] and optical sensors. [13][14][15][16][17] The emission of monomeric Pt(II) complexes arises mainly from metal-perturbed ligand-centered triplet states ( 3 MP-LC) as an admixture of 3 LC and 3 MLCT character (ligand-centered * and metal-to-ligand charge-transfer d*, respectively). Notably, Pt(II) complexes can form aggregates both in solution and in the solid state.…”

Tuning the luminescence of transition metal complexes with acyclic diaminocarbene ligands

“…Luminescent transition metal complexes underpin the development of OLEDs and other electroluminescent technologies (for the main reviews on the topic see ref. [1][2][3][4][5][6][7][8][9][10], and a broad range of applications in the fields of luminescence chemosensing, [11][12][13] photocatalysis, [14][15][16] sensitisation, [17][18][19] selfassembled materials, 20 and bioimaging. [20][21][22][23] Although pure organic light emitters are predominantly fluorescent (triplet excitons formed are deactivated by thermal processes), the presence of strong spin-orbit coupling in transition metal complexes upholds the intersystem crossing from the singlet to the triplet state enabling phosphorescent relaxation.…”

A 4′-(4-carboxyphenyl)-3,2′:6′,3′′-terpyridine-based luminescent cadmium(II) coordination polymer for the detection of 2,4,6-trinitrophenol

“…(Chakraborty & Mandal, 2017). NACs, such as 2,4,6-trinitrophenol (TNP), 2,4-dinitrophenol (2,4-DNP), dinitrotoluene (DNT), 1,3-dinitrobenzene (1,3-DNB) and nitrobenzene (NB), have been widely used in ISSN 2053ISSN -2296 # 2019 International Union of Crystallography the military, dye, agriculture and pharmaceutical industries (Chaudhari et al, 2013;Sathish et al, 2017). Furthermore, TNP can directly contaminate the soil and aquatic systems, and cause severe health problems, like liver or kidney damage, aplastic anemia, cyanosis and gastritis (Gao et al, 2017).…”