ABSTRACT
Three new cationic cyclometalated iridium(III) complexes equipped with differently substituted benzo[b]thiophen-2-ylquinoline cyclometalating ligands and with a sterically demanding tert-butyl-substituted 2,2'-bipyridine ancillary ligand were synthesized and structurally characterized by NMR and X-ray diffraction techniques. To tune the electronic properties of such complexes, the quinoline moiety of the cyclometalating ligands was kept pristine or equipped with electron-withdrawing phenyl and -CF3 substituents, leading to complexes 1, 2, and 3, respectively. A complete electrochemical and photophysical investigation, supported by density functional theory calculations, permits a deep understanding of their electronic properties. The emission of all complexes arises from ligand-centered triplet states in the spectral range between 625 and 950 nm, with excited-state lifetimes between 2.10 and 6.32 µs at 298 K. The unsubstituted complex (1) exhibits the most blue-shifted emission in polymeric matrix at 298 K (λmax = 667 nm, photoluminescence quantum yield (PLQY) = 0.25 and τ = 5.32 µs). The phenyl-substituted complex (2) displays the highest photoluminescent quantum yields (up to 0.30 in polymeric matrix), while the CF3-substituted counterpart (3) shows the most red-shifted emission, peaking at approx. 720 nm, but with lower quantum yields (e.g., 0.10 in polymeric matrix at 298 K). Complexes 1 and 2 were tested in single-layer nondoped light-emitting electrochemical cells (LEECs), using a nozzle-printing technique; both devices display deep-red electroluminescence with an external quantum efficiency close to 20%.
ABSTRACT
Toward the development of the smart biosensing drug carrier, integration of dye molecules with polymeric chain has been an emerging method in recent years. In this perspective, dipyridamole (Dip)-based branched poly(l-lactide) (PLLA) and branched polycaprolactone (PCL) have been synthesized by ring-opening polymerization. After polymerization, the influence of the polyester chains on the Dip emission behavior has been studied systematically in this work. Dip-PLLA has undergone C=O···N=C interaction in ground stage, leading to intramolecular charge transfer in the excited state. Limited availability of the C=O in PCL chains resists such interactions with Dip molecule. So, this structural availability of the C=O group in the polymeric chains influences the color change between Dip-PLLA (green fluorescence) and Dip-PCL (blue fluorescence). To visualize the biosensing ability of Dip-PLLA and Dip-PCL, hollow microspheres have been prepared by the double-emulsion solvent evaporation method, and the prepared microspheres cells uptake has been visualized by fluorescence imaging.
ABSTRACT
In this study, we report a synthetically simple donor-acceptor (D-A)-type organic solid-state emitter 1 that displays unique fluorescence switching under mechanical stimuli. Orange and yellow emissive crystals of 1 (1O, 1Y) exhibit an unusual "back and forth" fluorescence response to mechanical force. Gentle crushing (mild pressure) of the orange or yellow emissive crystal results in hypsochromic shift to cyan emissive fragments (λem = 498-501 nm) with a large wavelength shift Δλem = -71 to -96 nm, while further grinding results in bathochromic swing to green emissive powder λem = 540-550 nm, Δλem = +40 to 58 nm. Single-crystal X-ray diffraction study reveals that molecules are packed by weak interactions, such as C-H···π, C-H···N, and C-H···F, which facilitate intermolecular charge transfer in the crystal. With the aid of structural, spectroscopic, and morphological studies, we established the interplay between intermolecular and intramolecular charge-transfer interaction that is responsible for this elusive mechanochromic luminescence. Moreover, we have also demonstrated the application of this organic material for chlorine gas sensing in solid state.
