This review presents a robust strategy to design photosensitizers (PSs) for various species. Photodynamic therapy (PDT) is a photochemical-based treatment approach that involves the use of light combined with a light-activated chemical, referred to as a PS. Attractively, PDT is one of the alternatives to conventional cancer treatment due to its noninvasive nature, high cure rates, and low side effects. PSs play an important factor in photoinduced reactive oxygen species (ROS) generation. Although the concept of photosensitizer-based photodynamic therapy has been widely adopted for clinical trials and bioimaging, until now, to our surprise, there has been no relevant review article on rational designs of organic PSs for PDT. Furthermore, most of published review articles in PDT focused on nanomaterials and nanotechnology based on traditional PSs. Therefore, this review aimed at reporting recent strategies to develop innovative organic photosensitizers for enhanced photodynamic therapy, with each example described in detail instead of providing only a general overview, as is typically done in previous reviews of PDT, to provide intuitive, vivid, and specific insights to the readers.

Recent Strategies to Develop Innovative Photosensitizers for Enhanced Photodynamic Therapy.

Glucose Sensing in Supramolecular Chemistry

A novel approach toward the construction of multicomponent two-dimensional (2-D) and three-dimensional (3-D) metallosupramolecules is reported. Simply by mixing carboxylate and pyridyl ligands with cis-Pt(PEt3)2(OTf)2 in a proper ratio, coordination-driven self-assembly occurs, allowing for the selective generation of discrete multicomponent structures via charge separation on the metal centers. Using this method, a variety of 2-D rectangles and 3-D prisms were prepared under mild conditions. Moreover, multicomponent self-assembly can also be achieved by supramolecule-to-supramolecule transformations. The products were characterized by 31P and 1H multinuclear NMR spectroscopy, electrospray ionization mass spectrometry, and pulsed-field-gradient spin echo NMR techniques together with computational simulations.

A facile approach toward multicomponent supramolecular structures: selective self-assembly via charge separation.

A novel strategy was demonstrated to fabricate a luminescent lanthanide functionalized MOF by encapsulating Eu3+ cations in the pores of MIL-53–COOH (Al) nanocrystals. The Eu3+ incorporated sample shows excellent luminescence and good fluorescence stability in water due to the sensitization and protection provided by the parented framework. Subsequently, Eu3+ incorporated nanocrystals were developed as a highly selective and sensitive probe for detection of Fe3+ in aqueous solutions. In addition, the possible sensing mechanism based on cation exchange between Fe3+ and the framework Al3+ in MIL-53–COOH (Al) was discussed in detail. This is the first example for detecting Fe3+ in aqueous solutions based on a lanthanide functionalized nanoscale MOF. The good fluorescence stability in an aqueous environment, the low detection limit and the broad linear range, together with the nanoscale nature of this probe suggest it has potential for intracellular sensing and imaging of Fe3+.

An Eu3+ post-functionalized nanosized metal–organic framework for cation exchange-based

Herein some examples of the use of lanthanide ions (f-metal ions) to direct the synthesis of luminescent self-assembly systems (architectures) will be discussed. This area of lanthanide supramolecular chemistry is fast growing, thanks to the unique physical (magnetic and luminescent) and coordination properties of the lanthanides, which are often transferred to the resulting supermolecule. The emphasis herein will be on systems that are luminescent, and hence, generated by using either visibly emitting ions (such as EuIII, TbIII and SmIII) or near infrared emitting ions (like NdIII, YbIII and ErIII), formed through the use of templating chemistry, by employing structurally simple ligands, possessing oxygen and nitrogen coordinating moieties. As the lanthanides have high coordination requirements, their use often allows for the formation of coordination compounds and supramolecular systems such as bundles, grids, helicates and interlocked molecules that are not synthetically accessible through the use of other commonly used templating ions such as transition metal ions. Hence, the use of the rare-earth metal ions can lead to the formation of unique and stable species in both solution and in the solid state, as well as functional and responsive structures.

Lanthanide-directed synthesis of luminescent self-assembly supramolecular structures and mechanically bonded systems from acyclic coordinating organic ligands

A novel rhodamine B-based “off-on’’ fluorescent sensor for selective recognition of copper (II) ions

Self-assembly of cerium-based metal–organic tetrahedrons for size-selectively luminescent sensing natural saccharides

The development of DNA-targeted photodynamic therapy (PDT) agents for cancer treatment has drawn substantial attention. Herein, the design and synthesis of dinuclear IrIII -containing luminescent metallohelices with tunable PDT efficacy that target mitochondrial DNA in cancer cells are reported. The metallohelices are fabricated using dynamic imine-coupling chemistry between aldehyde end-capped fac-Ir(ppy)3 handles and linear alkanediamine spacers, followed by reduction of the imine linkages. The length and odd-even character of the diamine alkyl linker determined the stereochemistry (helicates vs. mesocates). Compared to the helicates, the mesocates exhibit improved apoptosis-induction upon white-light irradiation. Molecular docking studies indicate that the mesocate with a proper length of diamine spacers shows stronger affinity for the minor groove of DNA. This study highlights the potential of DNA-targeting IrIII -containing metallohelices as PDT agents.

Yang Jiao

Papers

A novel rhodamine B-based “off-on’’ fluorescent sensor for selective recognition of copper (II) ions

Self-assembly of cerium-based metal–organic tetrahedrons for size-selectively luminescent sensing natural saccharides

Mitochondrial-DNA-Targeted Ir III -Containing Metallohelices with Tunable Photodynamic Therapy Efficacy in Cancer Cells

A new fluorescent chemosensor for recognition of Hg2+ ions based on a coumarin derivative.

Fluorescent sensor for copper(II) ions based on coumarin derivative and its application in cell imaging