Excimer formation and evolution of excited state properties in discrete dimeric stacking of an anthracene derivative: a computational investigation

Pressure-Induced Blue-Shifted and Enhanced Emission: A Cooperative Effect between Aggregation-Induced Emission and Energy-Transfer Suppression

Most organic piezochromic materials exhibit red-shifted and quenched emission as pressure increases. However, an abnormal phenomenon of pressure-induced blue-shifted and enhanced emission is observed in a 9-(3-(1,2,2-triphenylvinyl)phenyl)anthracene crystal, which is based on discrete π-π anthracene (AN) dimers stacking with tetraphenylethylene (TPE) as spacer. A blue-shifted emission appears and strengthens when the pressure is more than 1.23 GPa, and it reaches the maximum when the pressure is 4.28 GPa. This phenomenon is ascribed to the cooperative effect between the aggregation-induced emission of TPE units and energy-transfer suppression from TPE to an AN excimer. This work reports a new concept in the piezochromic field and provides a novel strategy to achieve luminescence from a high-lying excited state.

Controlling the structure and photophysics of fluorophore dimers using multiple cucurbit[8]uril clampings

A modular strategy has been employed to develop a new class of fluorescent molecules, which generates discrete, dimeric stacked fluorophores upon complexation with multiple cucurbit[8]uril macrocycles. The multiple constraints result in a “static” complex (remaining as a single entity for more than 30 ms) and facilitate fluorophore coupling in the ground state, showing a significant bathochromic shift in absorption and emission. This modular design is surprisingly applicable and flexible and has been validated through an investigation of nine different fluorophore cores ranging in size, shape, and geometric variation of their clamping modules. All fluorescent dimers evaluated can be photo-excited to atypical excimer-like states with elongated excited lifetimes (up to 37 ns) and substantially high quantum yields (up to 1). This strategy offers a straightforward preparation of discrete fluorophore dimers, providing promising model systems with explicitly stable dimeric structures and tunable photophysical features, which can be utilized to study various intermolecular processes.

Dimerisation of a wide range of fluorophores through multiple CB[8] clampings leads to constrained intracomplex motion and distinct photophysical properties.

Efficient blue light emitting materials based on m-carborane-anthracene dyads. Structure, photophysics and bioimaging studies

Efficient monosubstitution of the non-iodinated, mono-iodinated and di-iodinated m-carborane cluster at one Ccluster has led to the preparation of three single organic molecule-carborane dyads (4-6), which exhibited exceptional fluorescence properties with quantum yield values of 100% in solution, for all of them, with maxima around 415 nm, which correspond to the locally excited state (LE) emission. These results suggest that simply linking the m-carborane fragment to one anthracene unit through a CH2 spacer produces a significant enhancement of the fluorescence in the final fluorophore, probably due to the free rotation of the anthracene linked to the Ccluster. Besides, the presence of one or two iodine atoms linked to boron atoms does not cause any influence on the photophysical properties of the dyads, as it is confirmed by TD-DFT calculations. Notably, the three conjugates show good fluorescence efficiency in the aggregate state with quantum yields in the range of 19-23%, which could be ascribed to the presence of CH2, particularly for 4, and the iodine atoms in 5 and 6, which prevent π-π stacking. All these results indicate that our dyads are extremely good emitters in solution while maintaining the emission properties in the aggregate state. Crystal packing, fingerprint plot analysis, and TD-DFT calculations for the three compounds support these results. Confocal microscopy studies show that 6 is the best-internalized compound by HeLa cells via endocytosis, although 4 and 5 also presented a high fluorescence intensity emission. Moreover, due to the blue emission, this compound is an excellent candidate to be applied as a fluorescent dye in bioimaging studies.

An Anthracene Excimer Fluorescence Probe on Mesoporous Silica for Dual Functions of Detection and Adsorption of Mercury (II) and Copper (II) with Biological In Vivo Applications

Dual functional activity by the same organic-inorganic hybrid material toward selective metal ion detection and its adsorption has drawn more attraction in the field of sensing. However, most of the hybrid materials in the literature are either for sensing studies or adsorption studies. In this manuscript, a fluorescent active hybrid material SiO₂ @PBATPA is synthesized by covalent coupling of anthracene-based chelating ligand N,N'-(propane-1,3-diyl) bis(N-(anthracen-9-ylmethyl)-2-((3-(triethoxysilyl)propyl) amino) acetamide) (PBATPA) within the mesopores of newly synthesized cubic mesoporous silica. The synthetic strategy is designed to form an exclusively intramolecular excimer on a solid surface, which is then used as a sensory tool for selective detection of metal ions through fluorescence quenching by the destruction of excimer upon metal ion binding. The dual functions of sensing and adsorption studies show selectivity toward Hg²⁺ and Cu²⁺ among various metal ions with detection limits of 37 and 6 ppb, respectively, and adsorption capacities of 482 and 246 mg g^-1 , respectively. This material can be used as a sensory cum adsorbent material in real food samples and living organisms such as the brine shrimp Artemia salina without any toxic effects from the material.

Unorthodox Combination of Cation-π and Charge-Transfer Interactions within a Donor-Acceptor Pair

Cation-π and charge-transfer (CT) interactions are ubiquitous in nature and involved in several biological processes. Although the origin of both the interactions in isolated pairs has extensively been studied, CT interactions are more prominent in supramolecular chemistry. Involvement of cation-π interactions in the preparation of advanced functional soft materials is uncommon. Moreover, a combination of these two interactions within a pair of electron donor (D) and acceptor (A) is uncharted. Here, we present a rational design to incorporate a combination of these two interactions within a D-A pair. A pyrene-peptide conjugate exhibits a combination of cation-π and CT interactions with a cationic naphthalenediimide (NDI) molecule in water. Nuclear Overhauser effect spectroscopy NMR along with other techniques and density functional theory calculations reveal the involvement of these interactions. The π-planes of pyrene and NDI adopt an angle of 56° to satisfy both the interactions, whereas β-sheet formation by the peptide sequence facilitates self-assembly. Notably, the binary system forms a self-supporting hydrogel at a higher concentration. The hydrogel shows efficient self-healing and injectable property. The hydrogel retains its thixotropic nature even at an elevated temperature. Broadly, we demonstrate a pathway that should prove pertinent to various areas, ranging from understanding biological assembly to peptide-based functional soft materials.

Unusual temperature-sensitive excimer fluorescence from discrete π–π dimer stacking of anthracene in a crystal

An unusual blue shift in excimer fluorescence with increasing temperature was observed from a crystal with a discrete π–π anthracene dimer.

Photo-irradiated E/Z isomerization reaction of star-shaped isomers containing two cyanostilbene arms with charge transfer excited states

The E/Z isomerization reaction of the multi-cyanostilbene molecule is still not clear. Herein, we have designed and synthesized three star-shaped molecular isomers with a triphenylamine core linked to two cyanostilbene groups with E/Z isomerization, Z,Z-TPDCF, Z,E-TPDCF and E,E-TPDCF, possessing three different isomeric molecular configurations, to investigate the specific E/Z isomerization reaction of the cyanostilbene groups in the two molecular arms. The in situ UV, 1H NMR and HPLC spectra under UV-irradiation clearly showed that the E/Z isomerization reactions of both E,E-TPDCF and Z,Z-TPDCF firstly turned them into Z,E-TPDCF, and the Z,E-TPDCF was almost simultaneously turned into more E,E-TPDCF and less Z,Z-TPDCF due to the calculated lowest unoccupied molecular orbitals of Z,E-TPDCF on the cyanostilbene arm with the Z-configuration. In general, Z,E-TPDCF exhibited a relatively better configurational stability than Z,Z-TPDCF or E,E-TPDCF under the photo-irradiation conditions. Further research demonstrated that all three isomers exhibited excellent aggregation-induced emission (AIE) properties.