Computational Insight into the Explosive Detection Mechanisms in Silafluorene- and Silole-Containing Photoluminescent Polymers

Poly(silafluorene-phenylenedivinylene)s and poly((tetraphenyl)-silole-phenylenedivinylene)s are promising materials for use in explosives detection. Monomers and dimers of silafluorene- and silole-containing polymers for the detection of nitro-containing explosives are modeled with M062X/6-31G(d). The geometric features of silafluorene- and silole-containing dimers optimized with M062X/6-31G(d) agree well with experimental findings. The binding properties of explosive and nonexplosive materials have been differentiated by comparing the relative stabilities of their complexes with silafluorene- and silole-containing dimers. The interactions that promote binding in the complexation of silafluorene- and silole-containing polymers with explosives are studied with a small model to shed light on the origin of the stability of the complexes. The topology of the electron density was analyzed using the quantum theory of atoms in molecules (QTAIM) methodology to understand the nature of the noncovalent interactions that are responsible for analyte-polymer binding. The carbon and germanium analogues of silafluorene-containing dimers are modeled to better understand the role of silicon in these polymeric systems. The calculated HOMO-LUMO energy differences of the complexes of dimers with explosives correlate well with the stability of the complexes; both (HOMO-LUMO and stability) support the selectivities of silafluorene- and silole-containing polymers. The stabilities of the complexes have shown that silafluorene-containing polymer detects the analytes in the order of 2,4,6-trinitrotoluene (TNT) similar to picric acid (PA) > 2,6-dinitrotoluene (DNT) > cyclotrimethylenetrinitramine (RDX) > nitrobenzene (NB), while the silole-containing polymer is able to detect the aromatic TNT but is not responsive to the nonaromatic RDX.