Near‐IR‐Triggered,Remote‐Controlled Release of Metal Ions: A Novel Strategy for Caged Ions

A ligand incorporating a dithioethenyl moiety is cleaved into fragments which have a lower metal‐ion affinity upon irradiation with low‐energy red/near‐IR light. The cleavage is a result of singlet oxygen generation which occurs on excitation of the photosensitizer modules. The method has many tunable factors that could make it a satisfactory caging strategy for metal ions.     

Target Enzyme‐Activated Two‐Photon Fluorescent Probes: A Case Study of CYP3A4 Using a Two‐Dimensional Design Strategy

The rapid development of fluorescent probes for monitoring target enzymes is still a great challenge owing to the lack of efficient ways to optimize a specific fluorophore. Herein, a practical two‐dimensional strategy was designed for the development of an isoform‐specific probe for CYP3A4, a key cytochrome P450 isoform responsible for the oxidation of most clinical drugs. In first dimension of the design strategy, a potential two‐photon fluorescent substrate ( NN ) for CYP3A4 was effectively selected using ensemble‐based virtual screening. In the second dimension, various substituent groups were introduced into NN to optimize the isoform‐selectivity and reactivity. Finally, with ideal selectivity and sensitivity, NEN was successfully applied to the real‐time detection of CYP3A4 in living cells and zebrafish. These findings suggested that our strategy is practical for developing an isoform‐specific probe for a target enzyme.     

Two‐Photon Fluorescent Probes for Metal Ions

Two‐photon microscopy (TPM) has become an indispensible tool in biology and medicine owing to the capability of imaging the intact tissue for a long period of time. To make it a versatile tool in biology, a variety of two‐photon probes for specific applications are needed. In this context, many research groups are developing two‐photon probes for various applications. In this Focus Review, we summarize recent results on model studies and selected examples of two‐photon probes that can detect intracellular free metal ions in live cells and tissues to provide a guideline for the design of useful two‐photon probes for various in vivo imaging applications.     

Dendrimer Conjugation Enables Multiphoton Chemical Neurophysiology Studies with an Extended π‐Electron Caging Chromophore

We have developed a caged neurotransmitter using an extended π‐electron chromophore for efficient multiphoton uncaging on living neurons. Widely studied in a chemical context, such chromophores are inherently bioincompatible due to their highly lipophilic character. Attachment of two polycarboxylate dendrimers, a method we call “cloaking”, to a bisstyrylthiophene (or BIST) core effectively transformed the chromophore into a water‐soluble optical probe, whilst maintaining the high two‐photon absorption of over 500 GM. Importantly, the cloaked caged compound was biologically inert at the high concentrations required for multiphoton chemical physiology. Thus, in contrast to non‐cloaked BIST compounds, the BIST‐caged neurotransmitter can be safely delivered onto neurons in acutely isolated brain slices, thereby enabling high‐resolution two‐photon uncaging without any side effects. We expect that our cloaking method will enable the development of new classes of cell‐compatible photolabile probes using a wide variety of extended π‐electron caging chromophores.     

From One‐Photon to Two‐Photon Probes: “Caged” Compounds,Actuators, and Photoswitches

Molecular systems that can be remotely controlled by light are gaining increasing importance in cell biology, physiology, and neurosciences because of the spatial and temporal precision that is achievable with laser microscopy. Two‐photon excitation has significant advantages deep in biological tissues, but raises problems in the design of “smart” probes compatible with cell physiology. This Review discusses the chemical challenges in generating suitable two‐photon probes.     

A Theoretical Investigation of Two Typical Two‐Photon pH Fluorescent Probes

Intracellular pH plays an important role in many cellular events, such as cell growth, endocytosis, cell adhesion and so on. Some pH fluorescent probes have been reported, but most of them are one‐photon fluorescent probes, studies about two‐photon fluorescent probes are very rare. In this work, the geometrical structure, electronic structure and one‐photon properties of a series of two‐photon pH fluorescent probes have been theoretically studied by using density functional theory (DFT) method. Their two‐photon absorption (TPA) properties are calculated using the method of ZINDO/sum‐over‐states method. Two types of two‐photon pH fluorescent probes have been investigated by theoretical methods. The mechanisms of the Photoinduced Charge Transfer (PCT) probes and the Photoinduced Electron Transfer (PET) probes are verified specifically. Some designed strategies of good two‐photon pH fluorescent probes are suggested on the basis of the investigated results of two mechanisms. For the PCT probes, substituting a stronger electron‐donating group for the terminal methoxyl group is an advisable choice to increase the TPA cross section. For the PET probes, the TPA cross sections increase upon protonation.     

Two‐Photon Absorption and the Design of Two‐Photon Dyes

Two photons are better than one : This principle applies to a wide range of applications, ranging from engineering to physiology. Recent advances in our understanding of the phenomenon of two‐photon absorption (see picture) and in the design of two‐photon dyes are rapidly increasing the scope of this field.

     

Polar Diketopyrrolopyrrole‐Imidazolium Salts as Selective Probes for Staining Mitochondria in Two‐Photon Fluorescence Microscopy

Three rationally designed polar derivatives of diketopyrrolopyrrole consisting of 1,3‐dimethylimidazolium cationic units and benzene, thiophene, or furan rings as π spacers were synthesized and thoroughly studied. The obtained salts are soluble in polar organic solvents and show satisfactory solubility in water, which makes them suitable for the applications in bioimaging. Photophysical measurements revealed that the obtained derivatives are characterized by strong absorption and good fluorescence quantum yields. The corresponding two‐photon properties were also examined and showed that the synthesized salts exhibit large two‐photon absorption cross‐sections reaching 4000 GM (GM=Goeppert‐Mayer unit, 1 GM=10^?50 cm⁴ s photon^?1) and very high two‐photon brightness values exceeding 2000 GM. It was demonstrated that these salts can be safely applied in two‐photon fluorescence microscopy for selective staining of mitochondria in living cells.