Controlled assembly of a bicyclic porphyrinoid and its 3-dimensional boron difluoride arrays

A fully conjugated cryptand-like bicyclic porphyrinoid ligand 4, incorporating three carbazole linkages and four dipyrrin moieties, was prepared via the acid-catalysed condensation of an extended 2,2′-bipyrrole analogue containing a central carbazole moiety and 3,4-diethyl-2,5-diformylpyrrole in 79% isolated yield. This new cryptand-like system acts as an effective ligand and allows for complexation of BF₂ (boron difluoride) subunits. Three BODIPY arrays, containing two, three, and four BF₂ subunits, namely 4·2BF₂, 4·3BF₂ and 4·4BF₂, could thus be isolated from the reaction of 4 with BF₃·Et₂O in the presence of triethylamine at 110 °C, albeit in relatively low yield. As prepared, bicycle 4 is characterized by a rigid C₂ symmetric structure as inferred from VT NMR spectroscopic analyses. In contrast, the three BODIPY-like arrays produced as the result of BF₂ complexation are conformationally flexible and unsymmetric in nature as deduced from similar analyses. All four products, namely 4, 4·2BF₂, 4·3BF₂ and 4·4BF₂, were characterized by means of single crystal X-ray diffraction analyses. Tetramer 4·4BF₂ gives rise to a higher extinction coefficient (by 2.5 times) relative to the bis- and tris-BODIPY arrays 4·2BF₂ and 4·3BF₂. This was taken as evidence for stronger excitonic coupling in the case of 4·4BF₂. All three BODIPY-like arrays proved nearly non-fluorescent, as expected given their conformationally mobile nature. The efficiency of reactive oxygen species (ROS) generation was also determined for the new BODIPY arrays of this study.

A cryptand-like bicyclic porphyrinoid was obtained in preference over the monocyclic porphyrinoid by controlling the reaction stoichiometry and condensation conditions. The cryptand-like species supports formation of multiple 3D BODIPY-like arrays.

Meso-Free Boron(III)subchlorin and Its μ-Oxo Dimer with Interacting Chromophores

Meso-free B(III)subchlorin 1 has been realized exclusively for the first time from meso-ethoxycarbonyl-substituted tripyrrane along with the first subchlorin dimer 2 as its μ-oxo analogue via a facile one-pot approach. The subchlorin is highly stable toward oxidation; hence, it was not contaminated with the corresponding subporphyrin analogue 3. The subchlorin (56%) and its dimer (30%) exhibit singlet oxygen generation ability for the first time. The B-O-B dimer displays strong exciton coupling between the two macrocycles.

Modulating the Optical Properties of BODIPY Dyes by Noncovalent Dimerization within a Flexible Coordination Cage

Aggregation of organic molecules can drastically affect their physicochemical properties. For instance, the optical properties of BODIPY dyes are inherently related to the degree of aggregation and the mutual orientation of BODIPY units within these aggregates. Whereas the noncovalent aggregation of various BODIPY dyes has been studied in diverse media, the ill-defined nature of these aggregates has made it difficult to elucidate the structure-property relationships. Here, we studied the encapsulation of three structurally simple BODIPY derivatives within the hydrophobic cavity of a water-soluble, flexible PdII6L4 coordination cage. The cavity size allowed for the selective encapsulation of two dye molecules, irrespective of the substitution pattern on the BODIPY core. Working with a model, a pentamethyl-substituted derivative, we found that the mutual orientation of two BODIPY units in the cage's cavity was remarkably similar to that in the crystalline state of the free dye, allowing us to isolate and characterize the smallest possible noncovalent H-type BODIPY aggregate, namely, an H-dimer. Interestingly, a CF3-substituted BODIPY, known for forming J-type aggregates, was also encapsulated as an H-dimer. Taking advantage of the dynamic nature of encapsulation, we developed a system in which reversible switching between H- and J-aggregates can be induced for multiple cycles simply by addition and subsequent destruction of the cage. We expect that the ability to rapidly and reversibly manipulate the optical properties of supramolecular inclusion complexes in aqueous media will open up avenues for developing detection systems that operate within biological environments.

Synthesis and Functions of Oligomeric and Multidentate Dipyrrin Derivatives and their Complexes

The dipyrrin–metal complexes and especially the boron complex 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) have recently attracted considerable attention because of their interesting properties and possible applications. We have developed two unique and useful ways to extend versatility and usefulness of the dipyrrin complexes. The first one is the linear and macrocyclic oligomerization of the BODIPY units. These arrangements of the B–F moieties of the oligomerized BODIPY units provide sophisticated functions, such as unique recognition ability toward cationic guest, associated with changes in the photophysical properties by utilizing unprecedented interactions between the B–F and a cationic species. The second one is introduction of additional ligating moieties into the dipyrrin skeleton. The multidentate N2Ox dipyrrin ligands thus obtained form a variety of complexes with 13 and 14 group elements, which are difficult to synthesize using the original N2 dipyrrin derivatives. Interestingly, these unique complexes exhibit novel structures, properties, and functions such as guest recognition, stimuli-responsive structural conversion, switching of the optical properties, excellent stability of the neutral radicals, etc. We believe that these multifunctional dipyrrin complexes will advance the basic chemistry of the dipyrrin complexes and develop their applications in the materials and medicinal chemistry fields.

1 Introduction

2 Linear Oligomers of Boron–Dipyrrin Complexes

3 Cyclic Oligomers of Boron–Dipyrrin Complexes

4 A Cyclic Oligomer of Zinc–Dipyrrin Complexes

5 Group 13 Element Complexes of N2Ox Dipyrrins

6 Chiral N2 and N2Ox Dipyrrin Complexes

7 Group 14 Element Complexes of N2O2 Dipyrrins

8 Other N2O2 Dipyrrin Complexes with Unique Properties and Functions

9 Conclusion

BODIPY-based macrocycles

During the past few years, the construction of BODIPY-based macrocycles has attracted extensive interest due to the widespread applications of these materials in sensing, bioimaging, molecular machines, and photodynamic therapy (PDT). Since significant progress has been made in this field, it is time to summarize the recent developments involving BODIPY-based macrocycles. In this review, we will briefly introduce the synthesis routes of BODIPY-based macrocycles, including a covalent synthetic protocol and a noncovalent self-assembly protocol. In addition, we will discuss the photophysical and photochemical properties and the applications of these BODIPY-based macrocycles in the areas of sensing, bioimaging, photodynamic therapy, etc.

Tuning the Photonic Behavior of Symmetrical bis-BODIPY Architectures: The Key Role of the Spacer Moiety

Herein we describe the synthesis, computationally assisted spectroscopy, and lasing properties of a new library of symmetric bridged bis-BODIPYs that differ in the nature of the spacer. Access to a series of BODIPY dimers is straightforward through synthetic modifications of the pending ortho-hydroxymethyl group of readily available C-8 (meso) ortho-hydroxymethyl phenyl BODIPYs. In this way, we have carried out the first systematic study of the photonic behavior of symmetric bridged bis-BODIPYs, which is effectively modulated by the length and/or stereoelectronic properties of the spacer unit. The designed bis-BODIPYs display bright fluorescence and laser emission in non-polar media. The fluorescence response is governed by the induction of a non-emissive intramolecular charge transfer (ICT) process, which is significantly enhanced in polar media. The effectiveness of the fluorescence quenching and also the prevailing charge transfer mechanism (from the spacer itself or between the BODIPY units) rely directly on the electron-releasing ability of the spacer. Moreover, the linker moiety can also promote intramolecular excitonic interactions, leading to excimer-like emission characterized by new spectral bands and the lengthening of lifetimes. The substantial influence of the bridging moiety on the emission behavior of these BODIPY dyads and their solvent-sensitivity highlight the intricate molecular dynamics upon excitation in multichromophoric systems. In this regard, the present work represents a breakthrough in the complex relationship between the molecular structure of the chromophores and their photophysical signatures, thus providing key guidelines for rationalizing the design of tailored bis-BODIPYs with potential advanced applications.

Switch-ON Near IR Fluorescent Dye Upon Protonation: Helically Twisted Bis(Boron Difluoride) Complex of π-Extended Corrorin

A novel helically twisted π-extended corrorin derivative having two boron dipyrrin (BODIPY) moieties at the periphery, a BODIPY DYEmer (6-BF₂ ) cross-bridged with π-conjugated dipyrrinylidene unit, was synthesized and characterized. The neutral 6-BF₂ is nonfluorescent due to the internal photoinduced charge transfer (CT) character in the excited state as inferred from the femtosecond transient absorption spectroscopy. However, upon protonation, the CT process is suppressed and the species H6-BF₂⁺ becomes near infrared (IR) emissive. With the aid of rigid helical conformations in 6-BF₂ , the helical isomers (P- and M-forms) were resolved and their chiroptical property was investigated. The distinct circular dichroism (CD) spectral changes of the enantiomers were observed in the presence of acids, which demonstrates that 6-BF₂ can be utilized for potential acid-responsive chiroptical materials.

Solvent-Sensitive Emitting Urea-Bridged bis-BODIPYs: Ready Access by a One-Pot Tandem Staudinger/Aza-Wittig Ureation

Herein we describe the synthesis, and computationally aided photophysical characterization of a new set of urea-bridged bis-BODIPY derivatives. These new dyads are efficiently obtained by a one-pot tandem Staudinger/aza-Wittig ureation protocol, from easily accessible meso-phenyl ortho-azidomethyl BODIPYs. These symmetric bis-BODIPYs outstand by a high absorption probability and excellent fluorescence and laser emission in less polar media. Nevertheless, this emission ability decreases in more polar media, which is ascribed to a light-induced charge-transfer from the urea spacer to the dipyrrin core, a process that can be modulated by appropriate changes in the substitution pattern of the BODIPY core. Furthermore, this ureation protocol can also be employed for the direct conjugation of our BODIPY-azides to amine-containing compounds, thus providing access to fluorescent non-symmetric ureas.

BODIPY dyes with thienyl- and dithienylthio-substituents – synthesis, redox and fluorescent properties

Novel thienyl- and dithienylthio-BODIPYs were synthesized, which displayed unusual crystal packing and luminescence.

Push–pull flexibly-bridged bis(haloBODIPYs): solvent and spacer switchable red emission

Uncommon flexibly-bridged bis(BODIPYs) displaying switchable red emission are described.