Phosphorescence Control Mediated by Molecular Rotation and Aurophilic Interactions in Amphidynamic Crystals of 1,4-Bis[tri-(p-fluorophenyl)phosphane-gold(I)-ethynyl]benzene

Fluorescence and Rotational Dynamics of a Crystalline Molecular Rotor Featuring an Aggregation-Induced Emission Fluorophore

Recent studies have shown that "crystal fluidity" in the form of fast conformational motions is critical for large-amplitude rotational motion in crystals. To explore this concept, we designed a crystalline assembly featuring two diethynylbenzene (DEB) molecular rotators linked to tetraphenylethylene (TPE), a fluorophore known to emit with intensities that depend on the rigidity of the medium. We envisioned that an increase in crystal fluidity as a function of increasing temperature would facilitate rotational motion of the DEB while diminishing the fluorescence intensity of the TPE. The aggregation-induced emission of the TPE moiety was confirmed when its fluorescence intensity increased by the addition of water to a THF solution. While bulk solids showed a relatively strong TPE emission with a lifetime of 4 ± 1 ns, no significant changes were observed between measurements carried out from 77 to 298 K, indicating that the crystal environment has limited motion within the excited-state lifetime. This conclusion was confirmed by the quadrupolar echo ²H NMR line-shape analysis of a deuterium-labeled sample between 198 and 298 K, which revealed rotational correlation times in the microsecond regime, suggesting that rotational fluidity is 3 orders of magnitude too slow to affect fluorescence emission.

Non-aromatic annulene-based aggregation-induced emission system via aromaticity reversal process

Aggregation-induced emission (AIE) is a photophysical phenomenon correlated closely with the excited-state intramolecular motions. Although AIE has attracted increasing attention due to the significant applications in biomedical and optoelectronics, an in-depth understanding of the excited-state intramolecular motion has yet to be fully developed. Here we found the non-aromatic annulene derivative of cyclooctatetrathiophene shows typical AIE phenomenon in spite of its rotor-free structure. The underlying mechanism is investigated through photoluminescence spectra, time-resolved absorption spectra, theoretical calculations, circular dichroism as well as by pressure-dependent fluorescent spectra etc., which indicate that the aromaticity reversal from ground state to the excited state serves as a driving force for inducing the excited-state intramolecular vibration, leading to the AIE phenomenon. Therefore, aromaticity reversal is demonstrated as a reliable strategy to develop vibrational AIE systems. This work also provides a new viewpoint to understand the excited-state intramolecular motion behavior of lumiongens.

Origin of the isotropic motion in crystalline molecular rotors with carbazole stators

Herein we report two crystalline molecular rotors 1 and 4 that show extremely narrow signals in deuterium solid-state NMR spectroscopy. Although this line shape is typically associated with fast-moving molecular components, our VT 2H NMR experiments, along with X-ray diffraction analyses and periodic DFT computations show that this spectroscopic feature can also be originated from low-frequency intramolecular rotations of the central phenylene with a cone angle of 54.7° that is attained by the cooperative motion of the entire structure that distorts the molecular axis to rotation. In contrast, two isomeric structures (2 and 3) do not show a noticeable intramolecular rotation, because their crystallographic arrays showed very restricting close contacts. Our findings clearly indicate that the multiple components and phase transitions in crystalline molecular machines can work in concert to achieve the desired motion.

Soft Crystals: Flexible Response Systems with High Structural Order

A new material concept of soft crystals is proposed. Soft crystals respond to gentle stimuli such as vapor exposure and rubbing but maintain their structural order and exhibit remarkable visual changes in their shape, color, and luminescence. Various interesting examples of soft crystals are introduced in the article. By exploring the interesting formation and phase-transition phenomena of soft crystals through interdisciplinary collaboration, new materials having both the characteristics of ordered hard crystals and those of flexible soft matter are expected.

Highly efficient photothermal nanoagent achieved by harvesting energy via excited-state intramolecular motion within nanoparticles

The exciting applications of molecular motion are still limited and are in urgent pursuit, although some fascinating concepts such as molecular motors and molecular machines have been proposed for years. Utilizing molecular motion in a nanoplatform for practical application has been scarcely explored due to some unconquered challenges such as how to achieve effective molecular motion in the aggregate state within nanoparticles. Here, we introduce a class of near infrared-absorbing organic molecules with intramolecular motion-induced photothermy inside nanoparticles, which enables most absorbed light energy to dissipate as heat. Such a property makes the nanoparticles a superior photoacoustic imaging agent compared to widely used methylene blue and semiconducting polymer nanoparticles and allow them for high-contrast photoacoustic imaging of tumours in live mice. This study not only provides a strategy for developing advanced photothermal/photoacoustic imaging nanoagents, but also enables molecular motion in a nanoplatform to find a way for practical application.

The effect of amorphization on the molecular motion of the 2-methylimidazolate linkers in ZIF-8

We investigated the effect of amorphization on the mobility of the organic linkers in a metal–organic framework.

Dielectric Relaxation of Powdered Molecular Gyrotops Having a Thiophene Dioxide-diyl as a Dipolar Rotor

The dielectric properties of powdered molecular gyrotops with a thiophenedioxide-diyl are reported. Crystals without a solvent molecule show usual dielectric relaxation spectra due to orientation polarization of the dipolar rotor, while a crystal having ethanol as the crystalline solvent molecule showed novel temperature-dependent dielectric relaxation switching by crystal-to-crystal phase transition, which is induced by hydrogen-bonding interactions between thiophene dioxide and ethanol.

Rise of Conjugated Poly-ynes and Poly(Metalla-ynes): From Design Through Synthesis to Structure-Property Relationships and Applications

Conjugated poly-ynes and poly(metalla-ynes) constitute an important class of new materials with potential application in various domains of science. The key factors responsible for the diverse usage of these materials is their intriguing and tunable chemical and photophysical properties. This review highlights fascinating advances made in the field of conjugated organic poly-ynes and poly(metalla-ynes) incorporating group 4-11 metals. This includes several important aspects of conjugated poly-ynes viz. synthetic protocols, bonding, electronic structure, nature of luminescence, structure-property relationships, diverse applications, and concluding remarks. Furthermore, we delineated the future directions and challenges in this particular area of research.

Dimesitylboryl-functionalised cyanostilbene derivatives of phenothiazine: distinctive polymorphism-dependent emission and mechanofluorochromism

Dimesitylborane-functionalized cyanostilbene derivatives of phenothiazine exhibit polymorphism with distinct solid-state emissions.

Exploiting rotational motion in molecular crystals

Rotational motion within molecular crystals is a prototypical concept to build future functional materials and solid-state molecular machines.

Correlating thermochromic and mechanochromic phosphorescence with polymorphs of a complex gold(i) double salt with infinite aurophilicity

Something learnt from a golden trio: polymorphs of a [Au(NHC)₂][Au(CN)₂] double salt allow an understanding of the thermochromic and mechanochromic phosphorescence of the gold(i) complexes with extended aurophilicity.