Chun-Lin Sun

Understanding the Unconventional Effects of Halogenation on the Luminescent Properties of Oligo(Phenylene Vinylene) Molecules

It is commonly known that halogenation tends to decrease the luminescence quantum yield of an organic dye, owing to the high electronegativity and heavy-atom effect of the halogen atom. However, based on an investigation of the effects of halogenation on the luminescence of the oligo(phenylene vinylene) (OPV) framework, we demonstrate that halogenation can have positive impact on the solid-state fluorescence and electrochemiluminescence (ECL) properties of OPV derivatives. The chlorinated OPV exhibits a very high solid-state fluorescence quantum yield (91%), whilst the brominated analogue gives the highest ECL emission intensity. Time-dependent density functional theory calculations, natural bond orbital analysis, and natural transition orbital analysis were performed to assist the understanding of the origin of these positive halogenation effects, which provide insight into the rational design of highly luminescent halogenated organic materials for solid-state devices and ECL applications.

Squaraines as light-capturing materials in photovoltaic cells

Photovoltaic cells are considered to be one of the most promising renewable energy sources of the 21st century. In particular, dye-sensitized solar cells (DSSCs) and organic photovoltaic devices (OPVs) are potentially the most economical and environmentally friendly ones. Squaraine (SQ) has intense absorption at 600–850 nm, exactly where sun flux is the most abundant. Furthermore, various substituents on SQ cores provide great possibilities for different molecular-design strategies. These characters make SQs ideal candidates for new DSSCs and OPVs. In response to the rapid development of SQ-based solar cells, a panorama of these ongoing studies is presented here, including the general synthetic routes of SQs and the various SQs used in DSSCs and OPVs. Our discussions are focused on the diverse molecular designs of SQs used in DSSCs and OPVs. The design strategies to acquire better light-harvesting abilities are also provided here, as well as the principles behind these strategies.

New molecular probe for the selective detection of zinc ion

A new multisignaling molecular probe DFDB was designed for the selective detection of Zn(2+). DFDB can be synthesized by a simple one-step reaction in high yield. Theoretical calculation suggests a novel sandwich structure of the DFDB·Zn(2+) complex.

An Electrochemically Switched Smart Surface for Peptide Immobilization and Conformation Control

We report an electrochemically switched smart surface for controlled peptide immobilization and conformation control. This dynamic surface is based on self-assembled monolayers (SAMs) containing surface-bound trimethoxybenzene moieties, which can undergo electrochemically modulated surface activation to be stepwisely converted to two catechol derivatives. This new smart surface can be used to realize stepwise immobilization of a peptide, and more importantly, to control peptide conformation on a surface. We demonstrate herein that with one electrochemical activation step, a linear peptide containing an RGD sequence can be attached onto the SAMs. With the subsequence activation step, the attached linear RGD peptide can be converted into cyclic conformation. The SAMs bounded with linear and cyclic RGD exhibit different adhesion behaviors to fibroblasts cells. The reaction procedure can be well-monitored by cyclic voltammetry (CV), electrochemical surface enhanced Raman microscopy (EC-SERS), and X-ray photoelectron spectroscopy (XPS). It is believed this robust smart surface can find wide applications in surface immobilization of bioactive moieties.

4,5,9,10-Pyrene Diimides: A Family of Aromatic Diimides Exhibiting High Electron Mobility and Two-Photon Excited Emission

The design and synthesis of high-performance n-type organic semiconductors are important for the development of future organic optoelectronics. Facile synthetic routes to reach the K-region of pyrene and produce 4,5,9,10-pyrene diimide (PyDI) derivatives are reported. The PyDI derivatives exhibited efficient electron transport properties, with the highest electron mobility of up to 3.08 cm2  V-1  s-1 . The tert-butyl-substituted compounds (t-PyDI) also showed good one- and two-photon excited fluorescence properties. The PyDI derivatives are a new family of aromatic diimides that may exhibit both high electron mobility and good light-emitting properties, thus making them excellent candidates for future optoelectronics.

Investigation of an Electrochemically Switched Heterocyclization Reaction on Gold Surface

We report an investigation of an electrochemically switched heterocyclization reaction on hydroquinone-terminated self-assembled monolayers (SAMs). This reaction involves an electrochemically modulated hydroquinone/benzoquinone transformation step in the SAMs and a subsequent heterocyclization step taking place between the electrochemically generated benzoquinone moieties in SAMs and l-cysteine in solution. The reaction process was monitored by XPS and electrochemical surface-enhanced Raman spectroscopy (EC-SERS). The surface reaction proceeds as a two-step reaction to give a benzothiazine product, which is in contrast to the much more complicated multiple step reactions in solution. This result suggests that the tight molecular packing in the SAMs does not hinder the intramolecular heterocylization reaction, but prevents the intermolecular coupling reaction from happening. This work provides insights to the control and detection of biomolecule related multistep reactions occurring at solid-liquid interface.

Surgery on Trichalcogenasumanenes: from π-Bowl to Planar, Invertible Curvature, and Chiral Polycycles

The buckybowl trichalcogenasumanenes show cleavage of flanking benzene ring upon oxidation, which leads their dissection by fusing various amidine moieties onto peripheral region. By gradually increasing the ring size of amidine from five- to six- and seven-membered, the molecule engineering results in the [7-5-6]-, [7-6-6]-, and [7-7-6]-fused polycycles. Three systems are distinct in the molecular geometries, packing motifs, and optoelectronic properties. The [7-5-6]-fused case adopts the flat backbone, displays strong emission with the fluorescence quantum yield up to 52.3 %, and undergoes a two-photon absorption process. The [7-6-6]-fused one is of a curvature with molecular geometry inversion, forms a tight stack of curved π-system, shows broad absorption extended to 700 nm, and exhibits the p-type semiconducting behavior with hole mobility of 4.4×10-3  cm2  V-1  s-1 . The [7-7-6]-fused one possesses the highly twisted skeleton to show stable chirality, and exhibits red emission in both solution and solid state. The surgery on trichalcogenasumanene is a promising approach to create polycycles with diverse functionalities.

Ultrabright organic fluorescent microparticles for in vivo tracing applications

We report the in vivo distribution, toxicity and metabolism of micro-sized fluorescent organic particles and their applications in cerebral blood flow tracing. The fluorescent microparticles exhibit bright fluorescence, good photo-stability and low toxicity; therefore, they are ideal for long-term non-invasive in vivo tracing. In contrast to conventional fluorescent labeling agents, which stain the entire blood vessel, the tracer microparticles can be easily tracked individually and provide vital information about blood flow behavior. Furthermore, we observed stimulated emission from these microparticles in living animals. These microparticles can provide unprecedented contrast for simultaneous observation of the distribution of blood vessels and the dynamics of microcirculation. Pathological examination revealed that the injected microparticles eventually collected in the spleen and liver. We found no observable toxicity of the microparticles to cells or mouse organs. We demonstrate that these fluorescent microparticles are suitable for applications in the field of non-intrusive blood flow tracing and could play a complementary role to traditional imaging agents.