Retention of Intrinsic Photophysical Properties of Porphyrin Building Blocks in 3D Organic Frameworks through Magic Angle Alignment.

Construction of three-dimensional (3D) frameworks maintaining intrinsic photophysical properties of monomeric building blocks is difficult and challenging due to the existence of various molecular interactions, such as metal-organic and π-π interactions. A 3D hydrogen-bonded organic framework (YSH-1Zn) with permanent porosity was constructed using a porphyrin having six carboxylic acid groups (1Zn). Brunauer-Emmett-Teller surface area measurement indicated that YSH-1Zn has a porous structure with a surface area of 392 m2/g. Single-crystal X-ray diffraction analysis revealed that 1Zn creates a 5-fold interwoven 3D network structure adopting a monoclinic system with a space group of P21/c. Each 1Zn within a single crystal exhibits parallel alignment with a slip-stack angle of 54.6°, in good agreement with the magic angle. Although the center-to-center distance of the nearest zinc atoms in YSH-1Zn is only 5.181 Å, the UV/vis absorption and fluorescence emission of YSH-1Zn are not different from those of 1Zn, indicating the absence of an interaction between excitons. Due to the magic angle alignment of 1Zn, the fluorescence lifetime, decay profiles, and quantum yield remained uniform even in the solid state.

High-Performance Near-Infrared Absorbing n-Type Porphyrin Acceptor for Organic Solar Cells.

While the outstanding charge transport and sunlight-harvesting properties of porphyrin molecules are highly attractive as active materials for organic photovoltaic (OPV) devices, the development of n-type porphyrin-based electron acceptors has been challenging. In this work, we developed a high-performance porphyrin-based electron acceptor for OPVs by substitution of four naphthalene diimide (NDI) units at the perimeter of a Zn-porphyrin (PZn) core using ethyne linkage. Effective π-conjugation between four NDI wings and the PZn core significantly broadened Q-band absorption to the near infrared region, thereby achieving the narrow band gap of 1.33 eV. Employing a windmill-structured tetra-NDI substituted PZn-based acceptor ( PZn-TNDI) and mid-band gap polymer donor (PTB7-Th), the bulk heterojunction OPV devices achieved a power conversion efficiency (PCE) of 8.15% with an energy loss of 0.61 eV. The PCE of our PZn-TNDI-based device was the highest among the reported OPVs using porphyrin-based acceptors. Notably, the amorphous characteristic of PZn-TNDI enabled optimization of the device performance without using any additive, which should make industrial fabrication simpler and cheaper.

Artificial light-harvesting n-type porphyrin for panchromatic organic photovoltaic devices.

A near-infrared-harvesting n-type porphyrin-based acceptor for organic photovoltaics (OPVs) was developed. The n-type acceptor, PDI-PZn-PDI, was designed by connecting a zinc porphyrin (PZn) core to two perylenediimide (PDI) wings through ethyne bridges. A narrow bandgap of 1.27 eV was achieved through the extended π-conjugation and intramolecular charge transfer between the strongly electron-donating PZn core and the electron-accepting PDI wings. A bulk heterojunction (BHJ) structured photovoltaic device fabricated from PDI-PZn-PDI with PTB7-Th exhibited panchromatic photon-to-current conversion from 350 to 900 nm. A power conversion efficiency of 5.25% with a remarkably low Eloss of 0.54 eV was achieved by optimizing the nanomorphology of the BHJ films by adding pyridine and by controlling the ZnO/BHJ interfacial properties.

Guest-Induced Modulation of the Energy Transfer Process in Porphyrin-Based Artificial Light Harvesting Dendrimers.

A series of dendritic multiporphyrin arrays (PZnTz-nPFB; n = 2, 4, 8) comprising a triazole-bearing focal zinc porphyrin (PZn) with a different number of freebase porphyrin (PFB) wings has been synthesized, and their photoinduced energy transfer process has been evaluated. UV/vis absorption, emission, and time-resolved fluorescence measurements indicated that efficient excitation energy transfer takes place from the focal PZn to PFB wings in PZnTz-nPFB's. The triazole-bearing PZn effectively formed host-guest complexes with anionic species by means of axial coordination with the aid of multiple C-H hydrogen bonds. By addition of various anionic guests to PZnTz and PZnTz-nPFB's, strong bathochromic shifts of PZn absorption were observed, indicating the HOMO-LUMO gap (ΔEHOMO-LUMO) of PZn decreased by anion binding. Time-resolved fluorescence measurements revealed that the fluorescence emission predominantly takes place from PZn in PZnTz-nPFB's after the addition of CN-. This change was reversible because a treatment with a silver strip to remove CN- fully recovered the original energy transfer process from the focal PZn to PFB wings.

Recent progress in the design and applications of fluorescence probes containing crown ethers.

Crown ethers, discovered by the winner of the Nobel Prize Charles Pedersen, are cyclic chemical compounds that consist of a ring or multiple rings containing several ether groups that are capable of binding alkali ions. A smart fluorescent probe containing a crown ether moiety could be developed as a sensor for metal ions, anions and other bio-molecules and be further applied to monitor the relevant biological process in vivo. This review highlights recent advances which can be divided into seven parts: (i) fluorescent probes containing a simple crown ether or an aza-crown ether structure; (ii) fluorescent probes containing an azathia crown ether; (iii) fluorescent probes containing a cryptand; (iv) fluorescent probes containing two or more binding sites; (v) crown ether derivatives-metal complex assisted chemosensing of bioactive species; (vi) crown ether-based chemosensors for bioactive molecular detection; and (vii) efforts to improve biological relevance.

Thermo-responsive poly(2-isopropyl-2-oxazoline) and tetraphenylethene hybrids for stimuli-responsive photoluminescence control.

Poly(2-isopropyl-2-oxazoline) (POx), a typical thermo-responsive polymer, was conjugated with a tetraphenylethene derivative, having aggregation induced emission behavior, towards the thermal control of their fluorescence emission. The poly(2-isopropyl-2-oxazoline)-tetraphenylethene hybrids selectively formed a host-guest complex with γ-cyclodextrin. The poly(2-isopropyl-2-oxazoline)-tetraphenylethene hybrids and its host-guest complex with γ-cyclodextrin showed opposite on-off switching of fluorescence emission upon temperature change.

Light-driven Au(III)-promoted cleavage of triazole-bearing amine derivatives and its application in the detection of ionic gold.

Light-driven Au(III)-promoted oxidative cleavage of triazole-bearing amine derivatives is utilized for the detection of ionic gold in aqueous media. A bistriazole-bearing boron dipyrromethane (1(BODIPY)) exhibited selective and sensitive fluorescence enhancement by the addition of Au(3+) and subsequent UV irradiation.

Photofunctional hollow nanocapsules for biomedical applications.

Among the various nano-objects, hollow nanocapsule systems offer fascinating formulations for biomedical applications. The hollow nanocapsule structures in this paper are divided into five different categories depending on their formation mechanism and structural components: (1) liposomes, (2) polymersomes and other polymeric hollow nanocapsules, (3) template-based hollow micro- and nanocapsules, (4) metallic hollow nanocapsules, and (5) other types of hollow nanocapsules. This feature article discusses the overall research trends in the design and applications of photofunctional hollow nanocapsules typically related to photodynamic therapy and photo-induced drug delivery.