No abstract

Here, we report the effects of electron donor and acceptor units attached with benzoselenadiazole for the change in optoelectronic and packing patterns in solid states. We have synthesized 4-methoxybenzene, naphthalene, and 4-nitrobenzene capped benzoselenadiazoles (compounds 1–3 respectively) and studied their photophysical as well as electrochemical properties. All three molecules show two absorption bands (π–π transition band and CT-band). Three molecules (1–3) show orange, yellow-green, and green colors in dichloromethane solutions upon irradiation of UV light at 365 nm. Benzoselenadiazole-based compounds 1–2 form head to head dimers via Se···N interactions in the solid states. Compounds 1 and 2 show interlock type packing via Se···N interaction in their solid state structures. Se···π interaction takes a major role to form interlocked sheet type structures in crystal packing of compound 1, whereas Se···N, N···N, and CH···π interactions help to form a supramolecular sheet type of structure in the crystal packing of compound 2. Band gaps of these compounds were tuned by changing the electron donating to electron withdrawing units attached with a benzoselenadiazole core.

A new bis-heteroleptic RuII complex (1­[PF 6 ] 2 ) with iodotriazole as the anion binding group along with the attached pyrene moiety is developed to investigate anion sensing properties and the origin of its selectivity toward a particular class of anions. Selective sensing of phosphates over other anions in both the solution and solid states by 1­[PF 6 ] 2 is clearly evident from the perturbation of the absorption band and a large degree of amplification of 3MLCT emission band in the presence of phosphates. Importantly, macroscopic investigation such as Scanning Electron Microscopy (SEM) and Dynamic Light Scattering (DLS) indicated the formation of supramolecular architecture in the presence of dihydrogen phosphate via halogen bonding interaction and π–π stacking of pyrene moieties. Such macroscopic property is further corroborated by solution and solid state spectroscopic studies, e.g., 1H-DOSY NMR, single crystal X-ray crystallography, and solid state photoluminescence (PL) spectroscopy.

An integrated urea and halogen bond donor based receptor is utilized for selective and superior sensing of phosphates.

A new molecular donor−acceptor−donor (D−A−D) triad, comprised of an electron deficient 1,4,5,8-naphthalene tetracarboxylic diimide (NDI) unit covalently connected to two flanking photosensitizers, i.e., a bis-heteroleptic Ru(II) complex of 1,10-phenanthroline and pyridine triazole hybrid ligand, is described. The single crystal X-ray structure of the perchlorate salt of the triad demonstrates that the electron deficient NDI unit can act as a host for anions via anion−π interaction. Detailed solutionstate studies indicate that fluoride selectively interacts with the D−A−D triad to form a dianionic NDI, NDI 2− , via a radical anion, NDI •− . On the contrary, cyanide reduces the NDI moiety to NDI •− , as confirmed by UV− vis, NMR, and EPR spectroscopy. Further, femtosecond transient absorption spectroscopic studies reveal a low luminescence quantum yield of the D−A−D triad attributable to the photoinduced electron transfer (PET) process from the photoactive Ru(II) center to the NDI unit. Interestingly, the triad displays "OFF−ON" luminescence behavior in the presence of fluoride by restoring the Ru(II) to phenanthroline/pyridine-triazole-based MLCT emission, whereas cyanide fails to show a similar property due to a different redox process operational in the latter. The reduction of NDI in the presence of fluoride and cyanide in different polar solvents indicates that involvement of such deprotonated solvents in the electron transfer mechanism may not be operative in our present system. Lowtemperature kinetic studies support the formation of a charge transfer associative transient species, which likely allows overcoming the thermodynamically uphill barrier for the direct electron transfer mechanism.