Paintable Hybrids with Thermally Stable Dual Emission Composed of Tetraphenylethene-Integrated POSS and MEH-PPV for Heat-Resistant White-Light Luminophores

Thermally stable dual emission followed by white-light luminescence from hybrid materials is reported. Hybrid films were prepared with a spin-coating method with the mixture solution containing tetraphenylethene (TPE)-integrated polyhedral oligomeric silsesquioxane (POSS) and poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV). TPE-tethered POSS (TPE-POSS) showed high compatibility with MEH-PPV. Therefore, homogeneous films with variable concentrations of TPE-POSS were obtained. Owing to good dispersion of rigid silica cubes into matrices, POSS-containing films demonstrated high thermal stability toward molecular rearrangement by annealing as well as pyrolysis, similar to conventional polymer hybrids. Furthermore, it was found that TPE-POSS was able to enhance emission efficiencies, probably by suppressing chain aggregation. By modulating introduction ratios of TPE-POSS, dual-emission properties followed by white-light luminescence composed of cyan and orange emissions from TPE-POSS and MEH-PPV, respectively, were accomplished. It should be noted that these color balances can be preserved even in the high-temperature region (425 K). Finally, white-light luminescent materials with thermal durability were obtained.

Aggregation-Induced Emission and White Luminescence from a Combination of π-Conjugated Donor-Acceptor Organic Luminogens

Two new star-shaped phenyl- and triazine-core based donor-acceptor (D-A) type conjugated molecules bearing triphenylamine end-capped arms were synthesized and characterized as imminent organic optoelectronic materials. Photophysical properties of the compounds were explored systematically via spectroscopic and theoretical methods. Because of the presence of donor-acceptor interactions, these luminogens display multifunctional properties, for instance, high extinction coefficient, large stokes shift, and pronounced solvatochromic effect. The compounds also exhibited phenomenon known as aggregation-induced emission on formation of nano-aggregates in the tetrahydrofuran-water mixture. The aggregate formation was confirmed by transmission electron microscopy, scanning electron microscopy, and dynamic light scattering analyses. Moreover, by controlling the electron withdrawing ability of the acceptor, complementary emissive fluorophores (blue and yellow) were achieved. These two complementary colors together span the entire range of visible spectrum (400-800 nm) and therefore when mixed in a requisite proportion generate white light in solution phase. These findings have potential for the progress of new organic white light radiating materials for applications in lighting and display devices.

Terminal Molecular Isomer-Effect on Supramolecular Self-Assembly System Based on Naphthalimide Derivative and Its Sensing Application for Mercury(II) and Iron(III) Ions

A series of naphthalimide derivative gelators (G-o, G-m, and G-p) with three molecular isomers as their terminal groups were designed and synthesized. Only G-m and G-p could form stable organogels in some solvents including methanol, acetonitrile, n-hexane, toluene, ethanol, DMSO, DMF, and mixed solvents of acetonitrile/H₂O (1/1, v/v). The different self-assembly structures were obtained from the self-assembly process of G-o, G-m, and G-p such as structures like a Chinese chestnut formed by irregular micrometer pieces, microbelts, and microbelt structures mingled with the bird's nest structures which exhibited different surface hydrophobicity with water contact angles of 121-139° due to their different intermolecular noncovalent interactions. To our surprise, G-p acetonitrile solution emitted 492 nm light with a red-shift of 72 nm compared with that emitted from G-o and G-m acetonitrile solution under 350 nm light excitation. Three gelators showed different detection abilities toward metal ions. G-o did not have any ability for sensitive and selective detection toward any ion. In contrast, G-m and G-p could sensitively and selectively detect Hg²⁺ and Fe³⁺. The detection limits for Fe³⁺ and Hg ²⁺ by G-m were 4.76 × 10^-5 M and 7.01 × 10^-6 M with the corresponding association constants ( K) of 1.64 × 10⁴ and 3.79 × 10⁴ M^-1, respectively. The detection limits for Fe³⁺ and Hg²⁺ by G-p were 3.26 × 10^-5 and 1.77 × 10^-6 M with the corresponding K of 1.44 × 10⁵ and 1.99 × 10⁴ M^-1, respectively. More interestingly, the back-titration of SCN^- could distinguish Hg²⁺ from Fe³⁺. At the same time, xerogels G-m and G-p also exhibited responsiveness toward Fe³⁺ and Hg²⁺ through fluorescence changes. The photophysical properties, gel formation, hierarchical structures, surface wettability, and their function in this self-assembly system could be tuned through the molecular isomer effect. This work provides a new research paradigm for molecular isomer tuned supramolecular self-assembly materials from noncovalent interaction to molecular function.

Ratiometric Indicator Based on Vibration-Induced Emission for in Situ and Real-Time Monitoring of Gelation Processes

Monitoring specific processes such as gelation in a ratiometric and visual manner is of scientific value and has practical implications but remains challenging. Herein, an innovative fluorescent low-molecular-weight gelator (DPAC-CHOL) capable of revealing and self-revealing the gelation processes in situ and in real time via the ratiometric fluorescence change from orange-red to blue has been developed. By virtue of its vibration-induced emission attribute, the gelation point, critical gelation concentration, and the internal stiffness of the gel networks of DPAC-CHOL and other gelation systems could be facilely evaluated in a ratiometric and naked-eye-observable fashion. Noteworthily, the DPAC-CHOL-doped gelation system Ph-CHOL can quantitatively identify the environmental temperature in a daily-concerned range (i.e., 20-55 °C). This work not only provides a versatile advanced material but also opens up a new avenue for the investigation of gelation systems.

A dual response organogel system based on an iridium complex and a Eu(iii) hybrid for volatile acid and organic amine vapors

A thiophene-based hybrid organogel system consisting of complex iridium (Ir) and EuCl₃·6H₂O was designed and synthesized to realize dual responses to volatile acids and organic amine vapors. The photophysical properties and self-assembly of compound 1 and the hybrid organogel were also studied. Compound 1 could gelate some organic solvents and self-assemble into 3D nanofibers in the gels. The stable hybrid organogel 1-Ir-Eu could be obtained after addition of complex Ir and EuCl₃·6H₂O. FTIR spectral results showed that the hydrogen bond still remained even upon addition of complex Ir, EuCl₃·6H₂O, NaOH and CF₃COOH to organogel 1. Interestingly, the emission properties of the hybrid organogel 1-Ir-Eu could undergo interconversion between cyan light and red light via addition of NaOH and CF₃COOH. The emission properties of xerogel film 1-Ir-Eu obtained in the presence of NaOH could also undergo fast and reversible transition in response to volatile acids such as CF₃COOH, formic acid, acetic acid, propionic acid and organic amine vapors such as ammonium hydroxide, Et₃N, tripropylamine, and ethylenediamine. The emission spectral change of Ir-Eu in the organogel or xerogel in the presence of base and acid demonstrated the formation of a new complex between complex Ir and EuCl₃·6H₂O. This dual-response process could be repeated many times. Contact angle experiment results further showed the morphology and internal components of the xerogel film surface in the process of response to gaseous CF₃COOH and Et₃N. This work provides a method for producing multifunctional supramolecular materials for sensing volatile acids and organic amine vapors.

Co-assembly of donor and acceptor towards organogels tuned by charge transfer interaction strength

Co-assembly of n-type semiconductors NDI and PDI with p-type pyrene derivatives resulted in the formation of stable organogels, which was induced by the strong charge transfer (CT) interactions between acceptors and donors in chloroform. The dimension size of the aromatic core from the acceptors was found to have a significant impact on the organogels. The width of the fibers from CT gels with NDI is about twice that from gels with PDI. It was found that the acceptor NDI preferred an alternate stacking with donors, intercalated with each other via CT interactions. In contrast, the acceptor PDI preferred to stack among themselves within the assemblies and this arose from the stronger π-π interactions because they had larger aromatic cores than the acceptor NDI. The dimension size of the aromatic core has been proved to have a significant impact on the organogels. The substituent impact of the donors was also studied.

White light emission by controlled mixing of carbon dots and rhodamine B for applications in optical thermometry and selective Fe3+detection

Controlled mixing of rhodamine B with fluorescent carbon dots derived from β-carotene resulted in a white light emitting mixture that could be used for optical thermometry and Fe³⁺ion detection in water.