David Reger

Seven donor and acceptor 2,6-disubstituted 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) dyes have been synthesized and characterized. Including MPBTCA, which is a known compound, the seven BODIPY dyes have been characterized by varied physical methods, such as UV/Visible absorption spectroscopy, low energy photo-electron spectroscopy (AC-2), and HOMO-LUMO DFT/TDDFT calculation. All seven BODIPY dyes have absorption λ_max around 535–545 nm, which is significantly longer than 499 nm of 4,4-difluoro-1,3,5,7,8-pentamethyl-4-bora-3a,4a-diaza-s-indacene (PM 546). Having structural variation on donor group, acceptor group, donor π-spacer, acceptor π-spacer, and the substituent on boron, some BODIPY dyes exhibit small extinction coefficients or spectral integrals in solution (MPCtBTCA, MPBT-pyO, MPBTT-pyO, MTBTCA), broadening absorption spectral profile (MTBTCA), weak intramolecular charge transfer characteristics (MPBT-pyO, MPBTT-pyO, MTBTCA), too low LUMO energy level (PPBTCA), or insufficient dye-uptake by TiO₂ FTO (MPBT-pyO, MPBTT-pyO, MTBTCA). Two of the seven BODIPY dyes, MPBTCA and MPBTTCA, do not show the adverse properties like other BODIPY dyes. With our improved TiO₂ FTO (fluorine doped tin oxide) dyeing method, namely a solution dropping method, high performance dye-sensitized solar cells (DSCs) have been realized by MPBTCA and MPBTTCA photosensitizers. Power conversion efficiencies of 6.3 and 6.4 % have been achieved by MPBTCA and MPBTTCA DSCs, respectively. To the best of our knowledge, MPBTCA and MPBTTCA are the most efficient dyes for the donor and acceptor 2,6-disubstituted BODIPY DSCs so far.

Dyeing to meet you: A series of 2,6-disubstituted BODIPY derivatives have been synthesized and characterized, and subsequently tested for use in dye-sensitized solar cells. Theoretical calculations and spectroscopic data suggest reasons for the improved performance, including a power conversion efficiency as high as 6.4% for MPBTTCA.

The radical arylation of anilines and pyrroles can be achieved under transition-metal- and catalyst-free conditions by using aryldiazotates in strongly alkaline aqueous solutions. The aryldiazotates act as protected diazonium ions, which do not undergo azo coupling with electron-rich aromatic substrates, but can still serve as an aryl radical source at slightly elevated temperatures. Based on an improved preparation of aryldiazotates in aqueous solution, homolytic aromatic substitutions of anilines and pyrroles were conducted with good overall yields and high regioselectivity. Moreover, DFT calculations provided further mechanistic insights.

It's all in the preparation! Based on an improved preparation of aryldiazotates, the arylation of anilines and 1-substituted pyrroles could be achieved under transition-metal- and catalyst-free conditions (see scheme). By combining experimental and computational results, this study gives insights into the particular features of the underlying reaction mechanism.

Two nickel-cornered organometallic metalla-rectangles containing a pyrene-linked-di-N-heterocyclic carbene have been prepared. The dimensions of one side of the rectangle were modulated by either using pyrazine or 4,4′-bipyridine. The two molecules were tested as hosts for the recognition of seven small polycyclic aromatic hydrocarbons (PAHs) in [D₆]acetone. By using ¹H NMR spectroscopy titrations, it could be established that the host–guest stoichiometries of the inclusion complexes formed were 1:1 for the pyrazine-based host, and 1:2 for the host containing bipyridine, in accordance with the larger dimensions of the latter. The molecular structure of the inclusion complex consisting of the bipyridine-containing host and pyrene was determined by X-ray crystallography, which confirms the 1:2 host–guest stoichiometry of this species. The determination of the association constants indicate that the binding strengths are in the order: Perylene<naphthalene<phenanthrene<anthracene<pyrene<triphenylene, ranging from 130–4400 m⁻¹ in the case of the smaller host, thus indicating that larger PAHs show higher binding strengths than smaller ones, except for the case of perylene, which exceeds the size for an optimum dimensional fitting within the cavity. As a proof of concept, the pyrazine host was used as a PAH-scavenger in heptane.

Be there or be square:Two nickel-cornered organometallic metalla-rectangles with a pyrene-linked di-N-heterocyclic carbene have been used for the selective recognition of small polycyclic aromatic hydrocarbons.

The synthesis of alternating donor–acceptor [12] and [16]cycloparaphenylenes (CPPs) has been achieved by the rhodium-catalyzed intermolecular cross-cyclotrimerization followed by imidation and/or aromatization. These alternating donor–acceptor CPPs showed positive solvatofluorochromic properties and smaller HOMO–LUMO gaps compared with nonfunctionalized CPPs, which was confirmed by the theoretical study.

Catherine wheels: The synthesis of alternating donor–acceptor [12] and [16]cycloparaphenylenes (CPPs) has been achieved by the rhodium-catalyzed intermolecular cross-cyclotrimerization followed by imidation and/or aromatization. The alternating donor–acceptor CPPs showed positive solvatofluorochromic properties and smaller HOMO–LUMO gaps compared with nonfunctionalized CPPs, which was confirmed by the theoretical study.

Because cellular uptake of anticancer Pt^II and Pt^IV drugs occurs by different mechanisms, the latter ones can exhibit substantial activity towards cells, which have either intrinsic or acquired resistance towards Pt^II drugs. However, this positive effect is diminished due to reductive activation of Pt^IV drugs in extracellular space that can be one of the reasons why they have not yet been approved for clinical use despite over 60 clinical trials conducted worldwide. Herein, we suggest a solution to this problem by achieving highly specific intracellular versus extracellular prodrug reduction. In particular, we prepared a hybrid Pt^IV prodrug containing two pro-reductants. This hybrid was uptaken by cells, the pro-reductants were activated in the cancer-specific microenvironment (high H₂O₂), and reduced Pt^IV by two one-electron transfers. The drug formed in this way induced cell death both in cisplatin-sensitive and resistant cell lines, but remained nontoxic to normal cells.

Reductive activation under oxidative conditions: A prodrug consisting of one Pt^IV center and two protected aminoferrocene-based pro-reductants was prepared. It was uptaken by cells, activated in the cancer-specific microenvironment (high H₂O₂) with reduction of Pt^IV via two intramolecular one-electron transfers. The drug formed in this way induced cell death both in cisplatin-sensitive and resistant cell lines (see scheme).

We report on a series of electron donor–acceptor conjugates incorporating a Zn^II–porphyrin-based electron donor and a variety of non-conjugated rigid linkers connecting to push–pull chromophores as electron acceptors. The electron acceptors comprize multicyanobutadienes or extended tetracyanoquinodimethane analogues with first reduction potentials ranging from −1.67 to −0.23 V vs. Fc⁺/Fc in CH₂Cl₂, which are accessible through a final-step cycloaddition–retroelectrocyclization (CA-RE) reaction. Characterization of the conjugates includes electrochemistry, spectroelectrochemistry, DFT calculations, and photophysical measurements in a range of solvents. The collected data allows for the construction of multiple Marcus curves that consider electron-acceptor strength, linker length, and solvent, with data points extending well into the inverted region. The enhancement of electron–vibration couplings, resulting from the rigid spacers and, in particular, multicyano-groups in the conformationally highly fixed push–pull acceptor chromophores affects the charge-recombination kinetics in the inverted region drastically.

Molecular photovoltaics: A series of electron donor–acceptor conjugates incorporating a Zn^II–porphyrin-based electron donor and multicyanobutadienes or extended tetracyanoquinodimethane analogues as electron acceptors with first reduction potentials ranging from −1.67 to −0.23 V vs. Fc⁺/Fc. As such, the rich redox chemistry, broad absorption in the visible and near infrared region, and electron-transfer behavior upon photoexcitation with charge recombination kinetics in the inverted region render these systems promising materials for applications in the field of molecular photovoltaics.