Suqian Ma

Highly Efficient Far Red/Near‐Infrared Solid Fluorophores: Aggregation‐Induced Emission, Intramolecular Charge Transfer, Twisted Molecular Conformation, and Bioimaging Applications

The development of organic fluorophores with efficient solid-state emissions or aggregated-state emissions in the red to near-infrared region is still challenging. Reported herein are fluorophores having aggregation-induced emission ranging from the orange to far red/near-infrared (FR/NIR) region. The bioimaging performance of the designed fluorophore is shown to have potential as FR/NIR fluorescent probes for biological applications.

An Organic Luminescent Molecule: What Will Happen When the “Butterflies” Come Together?

Cross dipole stacking based on a novel fluorescent molecule, 9,10-bis (2,2-diphenylvinyl) anthracene (BDPVA), is presented. The butterfly-like structure of BDPVA is the key feature to form the unique aggregation structure and such a stacking mode is highly beneficial for fluorescence emission, resulting in high-performance amplified spontaneous emission and electroluminescence of BDPVA.

Remarkable fluorescence change based on the protonation–deprotonation control in organic crystals

Insights into the origin of the fluorescence responsive to protonation-deprotonation stimuli were provided through the study on the crystals of a new stimuli-responsive molecule BP3VA. And the transformation between microcrystals demonstrated the varying emissions of the BP3VA powder.

Reversible Multistimuli-Response Fluorescent Switch Based on Tetraphenylethene–Spiropyran Molecules

Two tetraphenylethene (TPE)-functionalized spiropyran (SP) molecules with very similar structure were designed and synthesized. The two molecules exhibit aggregation-induced emission (AIE) properties, as well as multistimuli-responsive color-changing properties, such as photochromism and acidchromism. The investigation of their different photochromic and acidchromic characteristics and dual-response fluorescent switch during isomerization indicated that the different link position between TPE and SP will significantly affect the extended π-conjugated system, resulting in completely different photochromic and acidchromic properties.

Aggregation induced enhanced emission of conjugated dendrimers with a large intrinsic two-photon absorption cross-section

Organic nonlinear optical materials combining high luminescence quantum yields and large two-photon absorption cross-sections are attractive for both fundamental research and practical applications, such as up-converted lasers and two-photon fluorescence microscopy. Herein, we reported a series of conjugated dendrimers (AnG0, AnG1, and AnG2) which showed weak emissions in dilute solution due to the twisted intramolecular charge transfer (TICT) and free intramolecular rotational motion. On the contrary, high luminescence quantum yields (up to 0.85) have been observed in the nanoaggregated and solid-state because of the restriction of intramolecular rotation (RIR) and the more planar conformation, which has been demonstrated by experimental and theoretical investigations. These dendrimers possess an obviously large intrinsic two-photon absorption cross-section (up to 5180 GM), which is enhanced with the increase of the generation number. Due to the high solid-state luminescence quantum yields, an intense two-photon excited fluorescence with a larger Stokes shift can be obtained from these dendrimers as nanoaggregates and thin films. Thus, these dendrimers successfully provide large two-photon action cross-sections in the nanoaggregated or solid-state and have the potential for nonlinear optical applications.

Highly efficient near-infrared organic dots based on novel AEE fluorogen for specific cancer cell imaging

Near-infrared emissive organic dots with a high fluorescence quantum efficiency (AEE dots) are prepared by using an amphiphilic polymer poly(styrene-co-maleic anhydride) (PSMA) as the co-encapsulation matrix and a novel small molecule fluorogen (DPPBPA) with high near-infrared emission as the core. The PSMA dots show small particle size of about 20 nm, a large Stokes shift of 304 nm and really high fluorescence quantum efficiency of 20%. The streptavidin-dots are obtained by conjugating streptavidin to carboxyl groups on the surface of PSMA dots. These streptavidin-dots can effectively and specifically label the target cell without any nonspecific binding, such as MCF-7 cells. Together with the negligible cytotoxicity, the near-infrared emissive AEE dots are promising red fluorescent probes for future bioimaging applications.

Insights into the origin of aggregation enhanced emission of 9,10-distyrylanthracene derivatives

9,10-Distyrylanthracene (DSA) and its four derivatives are investigated by both steady state and ultrafast spectroscopy to reveal the intrinsic photophysical process upon excitation. Intramolecular rotation around the vinyl moiety plays an important role in the whole photophysical process in addition to the electronic properties of the peripheral substituents. In dilute solutions, DSA derivatives possess a twisted structure in the ground state that eventually relaxes to a planar structure within picoseconds. The fluorescence process is dominated by the relaxed excited state, and the quantum yield is affected by competition between the nonradiative and radiative deactivations. The enhanced fluorescence of the molecular aggregates originates from the optically allowed S1–S0 transition together with the suppressed nonradiative deactivation via molecular stacking. These findings provide an in-depth understanding of the origin of the aggregation enhanced emission process, and may be applicable for the fine design of DSA based molecules with enhanced fluorescence and novel structures beyond DSA.

Direct Observation of the Symmetrical and Asymmetrical Protonation States in Molecular Crystals

The symmetrical and asymmetrical protonation states are realized via the formation of intermolecular hydrogen bonds inside 9,10-bis((E)-2-(pyridin-4-yl)vinyl)anthracene (BP4VA) molecular crystals. With the protonation of H2SO4, BP4VA molecules are protonated symmetrically, while the molecules are asymmetrically protonated by introducing HCl. The different protonation states of BP4VA crystals result in various supramolecular interactions, aggregation states, and even tunable optical properties. It provides a fundamental principle to understand the effect of protonation in organic conjugated molecules and an approach to expanding the scope of organic functional materials.