Synthesis and Properties of Covalently Linked AzaBODIPY-BODIPY Dyads and AzaBODIPY-(BODIPY)2 Triads

Far-Red Excitation Induced Electron Transfer in Bis Donor-AzaBODIPY Push-Pull Systems; Role of Nitrogenous Donors in Promoting Charge Separation

A far-red absorbing sensitizer, BF2 -chelated azadipyrromethane (azaBODIPY) has been employed as an electron acceptor to synthesize a series of push-pull systems linked with different nitrogenous electron donors, viz., N,N-dimethylaniline (NND), triphenylamine (TPA), and phenothiazine (PTZ) via an acetylene linker. The structural integrity of the newly synthesized push-pull systems was established by spectroscopic, electrochemical, spectroelectrochemical, and DFT computational methods. Cyclic and differential pulse voltammetry studies revealed different redox states and helped in the estimation of the energies of the charge-separated states. Further, spectroelectrochemical studies performed in a thin-layer optical cell revealed diagnostic peaks of azaBODIPY⋅- in the visible and near-IR regions. Free-energy calculations revealed the charge separation from one of the covalently linked donors to the 1 azaBODIPY* to yield Donor⋅+ -azaBODIPY⋅- to be energetically favorable in a polar solvent, benzonitrile, and the frontier orbitals generated on the optimized structures helped in assessing such a conclusion. Consequently, the steady-state emission studies revealed quenching of the azaBODIPY fluorescence in all of the investigated push-pull systems in benzonitrile and to a lesser extent in mildly polar dichlorobenzene, and nonpolar toluene. The femtosecond pump-probe studies revealed the occurrence of excited charge transfer (CT) in nonpolar toluene while a complete charge separation (CS) for all three push-pull systems in polar benzonitrile. The CT/CS products populated the low-lying 3 azaBODIPY* prior to returning to the ground state. Global target (GloTarAn) analysis of the transient data revealed the lifetime of the final charge-separated states (CSS) to be 195 ps for NND-derived, 50 ps for TPA-derived, and 85 ps for PTZ-derived push-pull systems in benzonitrile.

Galantamine-Curcumin Hybrids as Dual-Site Binding Acetylcholinesterase Inhibitors

Galantamine (GAL) and curcumin (CU) are alkaloids used to improve symptomatically neurodegenerative conditions like Alzheimer's disease (AD). GAL acts mainly as an inhibitor of the enzyme acetylcholinesterase (AChE). CU binds to amyloid-beta (Aβ) oligomers and inhibits the formation of Aβ plaques. Here, we combine GAL core with CU fragments and design a combinatorial library of GAL-CU hybrids as dual-site binding AChE inhibitors. The designed hybrids are screened for optimal ADME properties and BBB permeability and docked on AChE. The 14 best performing compounds are synthesized and tested in vitro for neurotoxicity and anti-AChE activity. Five of them are less toxic than GAL and CU and show activities between 41 and 186 times higher than GAL.

Towards Efficient and Photostable Red-Emitting Photonic Materials Based on Symmetric All-BODIPY-Triads, -Pentads, and -Hexads

The development of efficient and stable red and near-IR emitting materials under hard radiation doses and/or prolonged times is a sought-after task due to their widespread applications in optoelectronics and biophotonics. To this aim, novel symmetric all-BODIPY-triads, -pentads, and -hexads have been designed and synthesized as light-harvesting arrays. These photonic materials are spectrally active in the 655-730 nm region and display high molar absorption across UV-visible region. Furthermore, they provide, to the best of our knowledge, the highest lasing efficiency (up to 68 %) and the highest photostability (tolerance >1300 GJ mol^-1 ) in the near-IR spectral region ever recorded under drastic pumping conditions. Additionally, the modular synthetic strategy to access the cassettes allows the systematic study of their photonic behavior related to structural factors. Collectively, the outstanding behavior of these multichromophoric photonic materials provides the keystone for engineering multifunctional systems to expedite the next generation of effective red optical materials.

Monofunctionalized 1,3,5,7-TetraarylazaBODIPYs and Their Application in the Synthesis of AzaBODIPY Based Conjugates

A series of monofunctionalized 1,3,5,7-tetraarylazaBODIPYs containing functional groups such as p-hydroxymethyl phenyl, p-hydroxyphenyl, p-cyanophenyl, p-nitrophenyl, and p-formylphenyl groups at the 1-position of the azaBODIPY core were synthesized by mixed condensation of two different nitrochalcones in n-butanol in the presence of CH₃COONH₄ at reflux followed by complexation with BF₃·OEt₂. The mixed condensation of nitrochalcones resulted in the formation of three different dipyrromethenes, which was treated with BF₃·OEt₂ to afford the desired monofunctionalized tetraarylazaBODIPYs in 30-36% yields. To demonstrate the application of monofunctionalized tetraarylazaBODIPYs, we reacted monoformyl functionalized tetraarylazaBODIPY with excess pyrrole to afford mono-dipyrromethanyl-substituted tetraarylazaBODIPY, which was used as a key precursor to prepare novel covalently linked azaBODIPY-based conjugates. The mono-dipyrromethanyl azaBODIPY was in situ oxidized with 2,3-dichloro-5,6-dicyanobenzoquinone and either reacted with BF₃·OEt₂ to afford azaBODIPY-BODIPY conjugates or reacted with metal salt such as Pd(acac)₂ to afford azaBODIPY-Pd(II)dipyrrin conjugates. Alternately, dipyrromethanyl-substituted azaBODIPY was condensed with dipyrromethane dicarbinol or 16-oxatripyrrane under mild acid catalyzed conditions followed by oxidation and chromatographic purification to afford azaBODIPY-porphyrin or azaBODIPY-oxasmaragdyrin conjugates, respectively. The photophysical studies on conjugates revealed that azaBODIPY is a good energy acceptor and invoked the possibility of energy transfer from the donor to acceptor in covalently linked conjugates.

β-AlkenylBODIPY Dyes: Regioselective Synthesis via Oxidative C-H Olefination, Photophysical Properties, and Bioimaging Studies

A series of 2-alkenyl- and 2,6-dialkenylboron dipyrromethene (BODIPY) derivatives were synthesized through Pd(II)-catalyzed regioselective and stereoselective oxidative C-H olefination in one step. The 2-alkenyl BODIPY derivative further reacted with various amines regioselectively at the 5-position through direct oxidative nucleophilic substitution. The photophysical properties of the 2-alkenyl- and 2,6-dialkenyl-substituted BODIPYs were investigated, which showed great potential in fluorescent bioimaging.

Photoinduced electron transfer and unusual environmental effects in fullerene–Zn-porphyrin–BODIPY triads

Molecular arrays containing donor–acceptor sites and antenna molecules are promising candidates for organic photovoltaic devices.