Well-defined dinuclear rhenium photocatalysts featuring an anthracene chromophore are significantly faster and more durable than their mononuclear counterparts.
Porphyrins
are attractive chromophores for application in dye-sensitized
solar cells (DSCs), as judicious tuning of donor–acceptor properties
can enable excellent near-infrared (NIR) absorption and exceptional
device performance. Here, we report a porphyrin-based dye (SM85) conjugated to the planar strong electron donor, indolizine, designed
to extend absorption further into the NIR region by inducing π–π
interactions such as head-to-tail dye aggregation. The optoelectronic
consequences of indolizine incorporation in SM85 include
raising the ground-state oxidation potential and broadening and red-shifting
ultraviolet–visible–NIR absorptions, along with increased
molar absorptivity when compared to the dye SM315. Density
functional theory (DFT) and time-dependent DFT (TD-DFT) calculations
confirm the push–pull character of SM85, which
features an overlap of frontier occupied and unoccupied orbitals.
Steady-state spectrophotometric analyses reveal the presence of solution
aggregates via absorption and emission spectroscopies. Aggregate modes
were probed by DFT and TD-DFT analyses, and plausible models are presented. SM85-based DSC devices demonstrate a 5.7% power conversion
efficiency (PCE) at full sun (7.4% PCE at 10% sun) with an exceptional
improvement to the incident photon-to-current conversion onset at
∼850 nm. Current dynamics measurements, time-correlated single
photon counting, and computational analyses are used to better understand
device performances. This study puts forward a novel intramolecular
charge-transfer porphyrin system with a dramatic shift into the NIR
region, as is needed for nonprecious metal-based sensitizers, and
provides an example of controlled, donor–acceptor-mediated
aggregation as a complementary strategy to traditional donor–acceptor
modifications to single-molecule π-systems in accessing enhancements
in long wavelength light harvesting in molecular-based optoelectronic
devices.
Re(pyNHC-PhCF 3 )(CO) 3 Br is a highly active photocatalyst for CO 2 reduction. The PhCF 3 derivative was previously empirically shown to be a robust catalyst. Here, the role of the PhCF 3 group is probed computationally and the robust nature of this catalyst is analyzed with regard to the presence of water and oxygen introduced in controlled amounts during the photocatalytic reduction of CO 2 to CO with visible light. This complex was found to work well from 0-1% water concentration reproducibly; however, trace amounts of water were required for benchmark Re(bpy)(CO) 3 Cl to give reproducible reactivity. When ambient air is added to the reaction mixture, the NHC complex was found to retain substantial performance (~50% of optimized reactivity) at up to 40% ambient atmosphere and 60% CO 2 while the Re(bpy)(CO) 3 Cl complex was found to give a dramatically reduced CO 2 reduction reactivity upon introduction of ambient atmosphere. Through the use of time-correlated single photon counting studies and prior electrochemical results, we reasoned that this enhanced catalyst resilience is due to a mechanistic difference between the NHC-and bpy-based catalysts. These results highlight an important feature of this NHC-ligated catalyst: substantially enhanced stability toward common reaction contaminates.
Desirable components for dye-sensitzed solar cell (DSC) sensitizers and fluorescent imaging dyes include strong donating building blocks coupled with well-balanced acceptor functionalities for absorption beyond the visible range. We have evaluated the effects of increasing acceptor strengths and incorporation of dye morphology controlling groups on molar absorptivity and absorption breadth with indolizine donor-based dyes. Indolizine-based D-A and D-π-A sensitizers incorporating bis-rhodanine, tricyanofuran (TCF), and cyanoacrylic acid functionalities were analyzed for performance in DSC devices. The TCF derivatives were also evaluated as near-infrared (NIR)-emissive materials with the AH25 emissions extending past 1000 nm.
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