2,5-difluorenyl-substituted siloles for the fabrication of high-performance yellow organic light-emitting diodes

Discs to a 'Bright' Future: Exploring Discotic Liquid Crystals in Organic Light Emitting Diodes in the Era of New-Age Smart Materials

With the advent of a new decade and the paradigm shift of every sphere of urban life to virtual platforms, it has become imperative for the global researcher community to channelize efforts into upgradation of the existing display-technology. In this context, discotic liquid crystals (DLCs) are a class of self-assembling organic materials that are recently being explored in fabricating the emissive layers of organic light emitting diodes (OLEDs). With their unique inherent structural and functional properties, they have the potential to challenge the currently prevailing OLED-emitters. Yet the applications of this promising class of materials in OLEDs have not been comprehensively reviewed in literature till now. In this account, we present an overview of the developments in the field of luminescent DLC-based emitters, supported by their associated photophysical phenomena and their performance parameters as emitters in fabricated OLED devices.

Conducting Silicone-Based Polymers and Their Application

Over the past two decades, both fundamental and applied research in conducting polymers have grown rapidly. Conducting polymers (CPs) are unique due to their ease of synthesis, environmental stability, and simple doping/dedoping chemistry. Electrically conductive silicone polymers are the current state-of-the-art for, e.g., optoelectronic materials. The combination of inorganic elements and organic polymers leads to a highly electrically conductive composite with improved thermal stability. Silicone-based materials have a set of extremely interesting properties, i.e., very low surface energy, excellent gas and moisture permeability, good heat stability, low-temperature flexibility, and biocompatibility. The most effective parameters constructing the physical properties of CPs are conjugation length, degree of crystallinity, and intra- and inter-chain interactions. Conducting polymers, owing to their ease of synthesis, remarkable environmental stability, and high conductivity in the doped form, have remained thoroughly studied due to their varied applications in fields like biological activity, drug release systems, rechargeable batteries, and sensors. For this reason, this review provides an overview of organosilicon polymers that have been reported over the past two decades.

Achieving yellow emission by varying the donor/acceptor units in rod-shaped fluorenyl-alkynyl based π-conjugated oligomers and their binuclear gold(i) alkynyl complexes

Fluorenyl-alkynyl based π-conjugated rod-shaped oligomers bearing different central aromatic moieties and functionalizable di-alkynyl termini, such as H-[triple bond, length as m-dash]-Fl-[triple bond, length as m-dash]-Fl-[triple bond, length as m-dash]-Fl-[triple bond, length as m-dash]-H (OH1), H-[triple bond, length as m-dash]-Fl-[triple bond, length as m-dash]-Btz-[triple bond, length as m-dash]-Fl-[triple bond, length as m-dash]-H (OH2) and H-[triple bond, length as m-dash]-Fl-[triple bond, length as m-dash]-Btd-[triple bond, length as m-dash]-Fl-[triple bond, length as m-dash]-H (OH3) where Fl = 9,9-dioctylfluorene, Btz = N-hexylbenzotriazole, and Btd = benzothiadiazole, were successfully synthesized by a Pd(0) catalyzed Stille coupling protocol. Electron withdrawing benzothiadiazole and benzotriazole as strong to moderate acceptors and fluorene as the donor have been incorporated to adjust the Donor-Acceptor (D-A) strength for fine-tuning the bandgap (E_g) as well as the emission wavelength. The corresponding digold(i) σ-complexes (PPh₃)Au-[triple bond, length as m-dash]-Fl-[triple bond, length as m-dash]-Fl-[triple bond, length as m-dash]-Fl-[triple bond, length as m-dash]-Au(PPh₃) (OM1), (PPh₃)Au-[triple bond, length as m-dash]-Fl-[triple bond, length as m-dash]-Btz-[triple bond, length as m-dash]-Fl-[triple bond, length as m-dash]-Au(PPh₃) (OM2) and (PPh₃)Au-[triple bond, length as m-dash]-Fl-[triple bond, length as m-dash]-Btd-[triple bond, length as m-dash]-Fl-[triple bond, length as m-dash]-Au(PPh₃) (OM3) have also been prepared by a reaction of Au(PPh₃)Cl and methanolic NaOMe in DCM with the corresponding alkynyl functionalized oligomers to take advantage of the heavy-atom effect on their emissive properties. The synthesized rod-shaped π-conjugated fluorene based oligomers and their binuclear Au(i) σ-complexes have been unambiguously characterized by various spectroscopic tools such as FTIR and multinuclear NMR as well as MALDI-TOF and CHN analyses. The absorption and emission spectral studies exhibited a progressive red shift with increasing the electron withdrawing character of the central aromatic unit. The rod-like oligomers having alkynyl termini and the corresponding digold(i) complexes are found to be blue, cyan and yellow emissive, demonstrating the fine-tuning of the emission wavelength. Most importantly, the fluorene based π-conjugated yellow light emitters OH3 and OM3 are successfully achieved by varying the donor/acceptor moiety to the fluorenyl-alkynyl backbone. The digold(i) diacetylide organometallic wires exhibit phosphorescence at 77 K in degassed CH₂Cl₂ due to the efficient intersystem crossing from the S₁ to the T₁ excited state as induced by heavy atoms.

A fluorescent cross-linked supramolecular network formed by orthogonal metal-coordination and host–guest interactions for multiple ratiometric sensing

A supramolecular network can be used for the ratiometric sensing of pH, cyclen and Cl⁻ due to the incorporation of two fluorophores and two non-covalent interactions.

Highly Efficient Nondoped OLEDs with Negligible Efficiency Roll-Off Fabricated from Aggregation-Induced Delayed Fluorescence Luminogens

Purely organic emitters that can efficiently utilize triplet excitons are highly desired to cut the cost of organic light-emitting diodes (OLEDs), but most of them require complicated doping techniques for their fabrication and suffer from severe efficiency roll-off. Herein, we developed novel luminogens with weak emission and negligible delayed fluorescence in solution but strong emission with prominent delayed components upon aggregate formation, giving rise to aggregation-induced delayed fluorescence (AIDF). The concentration-caused emission quenching and exciton annihilation are well-suppressed, which leads to high emission efficiencies and efficient exciton utilization in neat films. Their nondoped OLEDs provide excellent electroluminescence efficiencies of 59.1 cd A^-1 , 65.7 lm W^-1 , and 18.4 %, and a negligible current efficiency roll-off of 1.2 % at 1000 cd m^-2 . Exploring AIDF luminogens for the construction of nondoped OLEDs could be a promising strategy to advance device efficiency and stability.

Synthesis of 9,9'-Spirobifluorenes and 4,5-Diaza-9,9'-spirobifluorenes and Their Application as Affinity Materials for Quartz Crystal Microbalances

Two different classes of aza analogues of 9,9'-spirobifluorenes have been synthesized. These were obtained by either furnishing the spirobifluorene with additional pyridyl moieties or by installing the aza function directly into the spirobifluorene core. These structurally rigid compounds were then evaluated as affinity materials for quartz crystal microbalances and proved to be highly potent for the detection of volatile organic compounds.

Introductory lecture: recent research progress on aggregation-induced emission

Since the discovery of the aggregation-induced emission (AIE) phenomenon in 2001, research on AIE molecules has drawn much attention, and this area has been expanding tremendously. This brief review will focus on recent advances in the science and application of AIE molecules, including new mechanistic understanding, new AIE molecules for sensing and imaging, stimuli-responsive AIE molecules and applications of AIE molecules for OLEDs. Moreover, this review will give a perspective on the possible opportunities and challenges that exist in the future for this area.

A Significantly Twisted Spirocyclic Phosphine Oxide as a Universal Host for High-Efficiency Full-Color Thermally Activated Delayed Fluorescence Diodes

A universal thermally activated delayed fluorescence (TADF) host, 4'-diphenylphosphinoylspiro[fluorene-9,9'-xanthene] (SFXSPO), is constructed with a highly distorted and asymmetric configuration and disordered molecular packing in its solid state. SFXSPO successfully endows its full-color TADF diodes with state-of-the-art performance, e.g., the record external quantum efficiency of 22.5% and 19.1% and internal quantum efficiency of ≈100% for its yellow TADF diodes and single-host full-TADF nearly-white-emitting devices, respectively.

Silole-Based Red Fluorescent Organic Dots for Bright Two-Photon Fluorescence In vitro Cell and In vivo Blood Vessel Imaging

Robust luminescent dyes with efficient two-photon fluorescence are highly desirable for biological imaging applications, but those suitable for organic dots fabrication are still rare because of aggregation-caused quenching. In this work, a red fluorescent silole, 2,5-bis[5-(dimesitylboranyl)thiophen-2-yl]-1-methyl-1,3,4-triphenylsilole ((MesB)2 DTTPS), is synthesized and characterized. (MesB)2 DTTPS exhibits enhanced fluorescence efficiency in nanoaggregates, indicative of aggregation-enhanced emission (AEE). The organic dots fabricated by encapsulating (MesB)2 DTTPS within lipid-PEG show red fluorescence peaking at 598 nm and a high fluorescence quantum yield of 32%. Upon excitation at 820 nm, the dots show a large two-photon absorption cross section of 3.43 × 10(5) GM, which yields a two-photon action cross section of 1.09 × 10(5) GM. These (MesB)2 DTTPS dots show good biocompatibility and are successfully applied to one-photon and two-photon fluorescence imaging of MCF-7 cells and two-photon in vivo visualization of the blood vascular of mouse muscle in a high-contrast and noninvasive manner. Moreover, the 3D blood vasculature located at the mouse ear skin with a depth of over 100 μm can also be visualized clearly, providing the spatiotemporal information about the whole blood vascular network.

Aggregation-induced emission of siloles

Aggregation-induced emission (AIE) is a unique and significant photophysical phenomenon that differs greatly from the commonly acknowledged aggregation-caused emission quenching observed for many π-conjugated planar chromophores. The mechanistic decipherment of the AIE phenomenon is of high importance for the advance of new AIE systems and exploitation of their potential applications. Propeller-like 2,3,4,5-tetraphenylsiloles are archetypal AIE-active luminogens, and have been adopted as a core part in the design of numerous luminescent materials with diverse functionalities. In this review article, we elucidate the impacts of substituents on the AIE activity and shed light on the structure-property relationship of siloles, with the aim of promoting the judicious design of AIE-active functional materials in the future. Recent representative advances of new silole-based functional materials and their potential applications are reviewed as well.

Influences of Conjugation Extent on the Aggregation-Induced Emission Quantum Efficiency in Silole Derivatives: A Computational Study

The photophysical properties of a series of silole derivatives, with hydrogen (TPS), bromine (BrTPS), and conjugated phenyl (HPS), triphenylsilyethynyl (BTPES), and dimethylfluorene (BFTPS) substituents at 2,5-positions in both gas and aggregate phases have been investigated computationally by employing the correlation function rate formalism coupled with a hybrid quantum/molecular mechanics (QM/MM) approach. It is found that the solid-state fluorescence quantum efficiency first increases sharply with the degree of π-conjugation of the 2,5-substituents, then levels off, and finally starts to decrease slightly. This is because the side-group conjugation tends to enhance the radiative decay rate in both gas and solid phases. However, a further increase in conjugation leads to saturation in the radiative decay rate but increases the non-raditiave decay rate due to the decreased energy gap.

Modulation of aggregation-induced emission and electroluminescence of silole derivatives by a covalent bonding pattern

The deciphering of structure-property relationships is of high importance to rational design of functional molecules and to explore their potential applications. In this work, a series of silole derivatives substituted with benzo[b]thiophene (BT) at the 2,5-positions of the silole ring are synthesized and characterized. The experimental investigation reveals that the covalent bonding through the 2-position of BT (2-BT) with silole ring allows a better conjugation of the backbone than that achieved though the 5-position of BT (5-BT), and results in totally different emission behaviors. The silole derivatives with 5-BT groups are weakly fluorescent in solutions, but are induced to emit intensely in aggregates, presenting excellent aggregation-induced emission (AIE) characteristics. Those with 2-BT groups can fluoresce more strongly in solutions, but no obvious emission enhancements are found in aggregates, suggesting they are not AIE-active. Theoretical calculations disclose that the good conjugation lowers the rotational motions of BT groups, which enables the molecules to emit more efficiently in solutions. But the well-conjugated planar backbone is prone to form strong intermoelcular interactions in aggregates, which decreases the emission efficiency. Non-doped organic light-emitting diodes (OLEDs) are fabricated by using these siloles as emitters. AIE-active silole derivatives show much better elecroluminescence properties than those without the AIE characterisic, demonstrating the advantage of AIE-active emitters in OLED applications.

Aggregation-induced emission of a star-shape luminogen based on cyclohexanehexone substituted with AIE active tetraphenylethene functionality

A rigid star-shaped luminogen (HTCA) exhibits aggregation-induced emission (AIE) characteristics.

Di(naphthalen-2-yl)-1,2-diphenylethene-based conjugated polymers: aggregation-enhanced emission and explosive detection

Conjugated polymers with rotatable naphthalen-2-yl pendants show aggregation-enhanced emission characteristics and explosive detection potential.

Synthesis, structure, photoluminescence, and electroluminescence of siloles that contain planar fluorescent chromophores

Herein, a new series of siloles that were 2,5-substituted with planar fluorescent chromophores (PFCs), including fluorene, fluoranthene, naphthalene, pyrene, and anthracene, were synthesized and characterized. These compounds showed weak emission in the solution state, owing to active intramolecular rotation (IMR), but the synergistic effect from electronic coupling between the PFC and the silole ring compensated for the emission quenching by the IMR process to some extent, thereby affording higher emission efficiencies than those of 2,3,4,5-tetraphenylsiloles in solution. These new siloles showed enhanced emission efficiencies in the aggregated state. The electroluminescence (EL) color and efficiency of new siloles were sensitive towards the PFC. Siloles containing naphthalene moieties showed green EL emission, whilst those containing anthracene moieties showed orange EL emission. The siloles containing pyrene moieties exhibited yellow EL emission at 546 nm, with a peak luminance of 49000 cd cm(-2) and a high current efficiency of 9.1 cd A(-1).

Conjugation versus rotation: good conjugation weakens the aggregation-induced emission effect of siloles

Incorporation of polycyclic aromatic hydrocarbons into siloles enhances their light emission in solutions but lowers emission efficiency in the aggregated state. The competitive interaction between conjugation and rotation is thus studied.