Yulan Chen

A novel angularly fused bistetracene: facile synthesis, crystal packing and single-crystal field effect transistors

We report a facile synthesis of novel angularly fused bistetracene derivatives where two tetracene skeletons are cata-annulated at three benzene rings. Compared with previously described examples, our bistetracenes exhibit a narrower HOMO–LUMO gap but still exhibit high stability. Attempted synthesis of di-substituted bistetracene (BT-2TIPS) also led to unexpected triple (BT-3TIPS) and four-fold (BT-4TIPS) alkylsilylethynyl substitution. The photophysical, electrochemical and optical properties as well as the solid-state structure of these three bistetracene analogues are investigated. A charge carrier mobility up to 0.42 cm2 V−1 s−1 was determined based on field effect transistors.

Acid-Induced Multicolor Fluorescence of Pyridazine Derivative

Smart luminescent materials that are responsive to external stimuli have received considerable attention. Here, we report a new D-A type 1,2-pyridiazine derivative (3,4,5,6-tetrakis(4-methoxyphenyl)pyridazine (TPP)) exhibiting turn-on fluorescence upon acid exposure both in solution and in the solid state. The protonation of the 1,2-pyridiazine ring caused a variation in the emission colors of the acidification species from blue (406 nm) to orange-red (630 nm) with a huge Δλem (224 nm). As a result, a synthetic rainbow of emission in solution could be achieved from one single molecule, and white photoluminescence was readily tuned by controlled protonation. A trifluoroacetic acid (TFA)-sensor film made from TPP was demonstrated as a TFA-sensitive surface with high sensitivity and reversibility. On the basis of these findings, we constructed a solid-state TPP film with a photoacid generator and demonstrated data encryption and decryption via a cascade protonation reaction that was well controlled by UV light.

(Z)-Tetraphenylbut-2-ene-1,4-diones: facile synthesis, tunable aggregation-induced emission and fluorescence acid sensing

A facile approach to synthesize stereospecific (Z)-aryl-functionalized 1,4-enediones has been presented. The resulting molecules (TPBD-1 and TPBD-2) were demonstrated as a new type of heteroatom-containing AIE-active luminogens with multiple sites for structural modifications. Knoevenagel reaction of TPBD-1 led to a high electron affinity cyano derivative (TPBD-CN), which showed enhanced AIE performance and pronounced red-emission. More interestingly, TPBD-1 exhibited acid-induced red emission both in dilute solution and in the solid state, which is attractive due to its great potential for turn-on optical sensing. The reversible fluorescence acid sensing can be attributed to the stepwise binding effect of carbonyl groups on the 1,4-enedione core to rigidify the molecular conformation and strengthen the D–A interaction, which was systematically investigated by UV-vis, FL, FT-IR, and NMR spectroscopy and was further corroborated by DFT calculations.

Dual-responsive BN-embedded phenacenes featuring mechanochromic luminescence and ratiometric sensing of fluoride ions

A series of novel dual-responsive BN-embedded phenacenes were designed and synthesized, via N-directed borylation of donor–acceptor–donor (D–A–D) precursors as the key step. Their crystal structures, and photophysical and electrical properties were systematically studied, which were found to be highly dependent on the incorporated BN units and fused aromatic rings with varied electron density. For the first time, mechanochromic luminescent (MCL) properties of BN-embedded phenacenes were realized, which are regulated jointly by inter- and intra-molecular effects at the molecular level. In the solid state, their emission colors can be tuned reversibly by external force, and interestingly, they exhibit an unusual hypochromic shift after grinding. Furthermore, in solution, these BN-containing phenacenes enable colorimetric and fluorometric detection of fluoride ions with high selectivity and a low detection limit of down to 1.8 × 10−8 M. The dual-responsive properties of these compounds highlight the widespread applications of BN containing conjugated materials in optical sensors.

From S,N‐Heteroacene to Large Discotic Polycyclic Aromatic Hydrocarbons (PAHs): Liquid Crystal versus Plastic Crystalline Materials with Tunable Mechanochromic Fluorescence

A novel type of discotic polycyclic aromatic hydrocarbon (PAH) based on an enlarged dibenzo[a,c]phenazine core has been developed. The large conjugated mesogenic core with increased dipole moment derived from S,N heteroatoms facilitates the formation of highly ordered columnar superstructures both in solution and bulk. Columnar mesophases, including liquid crystal (LC) and plastic crystal (PC) assemblies could form unprecedentedly based on the same PAH core. The cores are delicately modulated by the peripherical alkoxy chains. Both mesogens have mechanochromic fluorescent (MCF) character, which is also structure dependent and correlated with the different mesophase formation. For the first time, MCF properties can be realized in such a large conjugated mesogenic system.