High solid-state fluorescence in ring-shaped AEE-active tetraphenylsilole derivatives

Abstract

Three ring-shaped AEE-active silole-containing compounds were synthesized by mild condensation reactions. Cyclotrisiloxane compound 1 displays high solid-state quantum yield (Φfl = 0.86) with the fluorescence maximum at 512 nm. This high fluorescence efficiency results mainly from decreased vibrational pathways to fluorescence decay due to the intramolecular C-H···π interactions.

Understanding and Tailoring Excited State Properties in Solution-Processable Oligo(p-phenyleneethynylene)s: Highly Fluorescent Hybridized Local and Charge Transfer Character via Experiment and Theory

“…The solid-state quantum efficiencies for both neat thin-film and single-crystal were measured to be very high (Φ PL‑solid state ∼ 0.78 and 0.81, respectively) using an integrating sphere method. The observed high solid-state quantum yield in the single-crystal is consistent with the presence of multiple strong C–H···π interactions and the absence of π–π interactions in the crystal lattice ( vide supra ), both of which prevents unfavorable fluorescence decays via exciton-vibronic/phonon couplings . Here, we note that similar short-range interactions were also evident in the XRD characterization (a broad peak with 2θ = 16–29° in Figure S14) of the spin-coated neat thin-film, which apparently contributes to the observed high fluorescence efficiency in thin-film phase even though long-range ordering is not present.…”

“…The observed high solid-state quantum yield in the single-crystal is consistent with the presence of multiple strong C−H•••π interactions and the absence of π−π interactions in the crystal lattice (vide supra), both of which prevents unfavorable fluorescence decays via exciton-vibronic/phonon couplings. 53 Here, we note that similar short-range interactions were also evident in the XRD characterization (a broad peak with 2θ = 16−29°in Figure S14) of the spin-coated neat thin-film, which apparently contributes to the observed high fluorescence efficiency in thin-film phase even though long-range ordering is not present. As shown in Figure 7b, 2EHO-TPA-PE-doped PS and PMMA thin-films showed very similar decay profiles to those observed in the medium-polarity solvents with major prompt decays (0.85 ns (99.75%) and 0.81 ns (98.39%), respectively) followed by minor delayed decay channels (4.09 ns (0.25%) and 2.57 ns (1.61%), respectively).…”

“…As shown in Figure c, these interactions are indeed enabled by the presence of intramolecular twists that directs each ( phenylene )­C–H bond into a favorable position to interact with the phenylene/ethynylene unit of the adjacent molecule, which also helps to extend one-dimensional slipped stack π-network into a 3D crystal structure. The observed solid-state microstructure for the new molecule with multiple (14 interactions in the dimeric form) strong C–H···π interactions makes the π-structures and the crystal lattice very rigid and precludes possible vibronic pathways to fluorescence decay in the solid-state by reducing exciton-vibronic couplings. , On the other hand, short π–π interactions are typically linked to increased exciton–phonon couplings, resulting in unfavorable fluorescence decays in the solid-state. , Therefore, the absence of π–π interactions in our case, along with the presence of multiple strong C–H···π interactions, are expected to lead to high quantum efficiencies in the solid-state (Φ PL‑solid state = 0.80, vide infra ) . When the solid-state packing and the photoluminescence quantum efficiency of the new molecule is compared with those of our previously reported 2EHO-CNPE , we see that 2EHO-CNPE shows a much reduced Φ PL‑solid state of 0.50 associated with a significantly reduced degree of intermolecular C–H···π interactions …”

“…The observed solid-state microstructure for the new molecule with multiple (14 interactions in the dimeric form) strong C−H•••π interactions makes the π-structures and the crystal lattice very rigid and precludes possible vibronic pathways to fluorescence decay in the solid-state by reducing exciton-vibronic couplings. 53,54 On the other hand, short π−π interactions are typically linked to increased exciton−phonon couplings, resulting in unfavorable fluorescence decays in the solid-state. 55,56 Therefore, the absence of π−π interactions in our case, along with the presence of multiple strong C−H•••π interactions, are expected to lead to high quantum efficiencies in the solid-state (Φ PL-solid state = 0.80, vide infra).…”

Synthesis and High Solid-State Fluorescence of Cyclic Silole Derivatives

“…Siloles–a class of silicon-containing compounds analogous to cyclopentadiene with a remarkably small HOMO–LUMO gap, intrinsically high electron mobility, favorable photophysical properties (near UV to blue light emission peak range: 350–520 nm), and high fluorescence efficienciesare nowadays among the most popular and promising structural building blocks in molecular and polymer-based materials used for manufacturing high-performance electro- and photoluminescent devices. , Given the high degree of their structural variability, their electronic and optical properties can be tuned through a multitude of methods such as polymerization, , attaching conjugating substituents or highly fluorescent groups to the silicon atom, and structural modification of peripheral phenyl moieties . Previously, we demonstrated that well-known silole derivatives combined with highly fluorescent bis(diquinaldinatoalumino) ligands yield compounds displaying a 4- to 6-fold increase in solid-state fluorescence efficiency. − Against the backdrop of our latest discovery that highly fluorescent ring-shaped siloxanes containing exclusively silole-based fluorophorstetraphenylsilole (Scheme a) or silafluorene (Scheme b)are easily accessible through a simple cohydrolysis reaction between corresponding dichlorosilole derivatives and dichlorosilane under ambient conditions, , it appeared of interest to us to test if combining different fluorogenic units in this structural framework would have a similar effect on the fluorescence efficiencies of their derivatives. We thus set out to extend our studies of ring-shaped silole derivatives and their photophysical properties by synthesizing a series of near-UV or blue-light-emitting compounds containing well-known fluorogenic units such as phenyl, 1,3-diphenyl-9-silafluorene (Scheme c), 9-silafluorene, and tetraphenylsilole in the siloxane framework.…”