Five new chromophore–tetrapyrrole arrays bearing an ethynyl linker have been synthesized to explore the effects of chromophore nature and tetrapyrrole attachment site on panchromatic spectral properties.
Three sets of tetrapyrrole-chromophore arrays have been examined that exhibit panchromatic absorption across large portions of the near-ultraviolet (NUV) to near-infrared (NIR) spectrum along with favorable excited-state properties for use in solar-energy conversion. The arrays vary the tetrapyrrole (porphyrin, chlorin, bacteriochlorin), chromophore (boron-dipyrrin, perylene, terrylene), and attachment sites (meso-position, β-pyrrole position). In all, seven dyads, one triad, and nine benchmarks in toluene and benzonitrile were studied using steady-state and time-resolved absorption and fluorescence spectroscopy. The results were analyzed with the aid of density functional theory (DFT) and time-dependent DFT calculations. Natural transition orbitals (NTOs) were constructed to assess the net change in electron density associated with each NUV-NIR absorption transition. The porphyrin-perylene dyad P-PMI displays the most even spectral coverage from 400 to 700 nm, with an average ε ∼ 43 000 M cm. A significant contributor is a chromophore-induced reduction in the configuration interaction involving the four frontier molecular orbitals of benchmark porphyrins and associated constructive/destructive transition-dipole interference that results in intense (ε ∼ 400 000 M cm) NUV and weak (<20 000 M cm) visible features. P-PMI has an S lifetime (τ) of 4.7 ns in toluene and 1.3 ns in benzonitrile. Bacteriochlorin analogue BC-PMI has more extended spectral coverage (350-750 nm) and τ = 2.8 ns in toluene and 30 ps in benzonitrile. Terrylene analogue P-TMI has intermediate optical characteristics with τ = 310 ps in toluene and 150 ps in benzonitrile. The NTOs for most arrays show that S → S primarily involves the tetrapyrrole, but for P-TMI the NTOs have electron density delocalized over the two units as a result of extensive orbital mixing. Collectively, the insights obtained should aid the design of tetrapyrrole-based architectures for panchromatic light-harvesting systems for solar-energy conversion.
While
metal–organic frameworks (MOFs) have been under thorough
investigation over the past two decades, photoconductive MOFs
are an emerging class of materials with promising applications in
light harvesting and photocatalysis. To date, there is not a general
method to investigate the photoconductivity of polycrystalline MOF
samples as-prepared. Herein, we utilize time-resolved terahertz spectroscopy
along with a new sample preparation method to determine the photoconductivity
of Zn2TTFTB, an archetypical conductive MOF, in a noncontact
manner. Using this technique, we were able to gain insight into MOF
photoconductivity dynamics with subpicosecond resolution, revealing
two distinct carrier lifetimes of 0.6 and 31 ps and a long-lived component
of several ns. Additionally, we determined the frequency dependent
photoconductivity of Zn2TTFTB which was shown to follow
Drude–Smith behavior. Such insights are crucially important
with regard to developing the next generation of functional photoconductive
MOF materials.
Electrocatalytic ammonia oxidation
at room temperature and pressure
allows energy-economical and environmentally friendly production of
nitrites and nitrates. Few molecular catalysts, however, have been
developed for this six- or eight-electron oxidation process. We now
report [Cu(bipyalk)]+, a homogeneous electrocatalyst that
realizes the title reaction in water at 94% Faradaic efficiency. The
catalyst exhibits high selectivity against water oxidation in aqueous
media, as [Cu(bipyalk)]+ is not competent for water oxidation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.