Chlorophyll (Chl) derivatives have recently been proposed as photoactive materials in next-generation bio-inspired solar cells, because of their natural abundance, environmental friendliness, excellent photoelectric performance, and biodegradability. However, the intrinsic excitation dynamics of Chl derivatives remain unclear. Here, we show sub-nanosecond pump–probe time-resolved absorption spectroscopy of Chl derivatives both in solution and solid film states. We observe the formation of triplet-excited states of Chl derivatives both in deoxygenated solutions and in film samples by adding all-trans-β-carotene as a triplet scavenger. In addition, radical species of the Chl derivatives in solution were identified by adding hydroquinone as a cation radical scavenger and/or anion radical donor. These radical species (either cations or anions) can become carriers in Chl-derivative-based solar cells. Remarkably, the introduction of hydroquinone to the film samples enhanced the carrier lifetimes and the power conversion efficiency of Chl-based solar cells by 20% (from pristine 1.29% to 1.55%). This enhancement is due to a charge recombination process of Chl-A+/Chl-D–, which is based on the natural Z-scheme process of photosynthesis.
In bacterial photosynthesis, the excitation energy transfer (EET) from carotenoids to bacteriochlorophyll a has a significant impact on the overall efficiency of the primary photosynthetic process. This efficiency can be enhanced when the involved carotenoid has intramolecular charge-transfer (ICT) character, as found in light-harvesting systems of marine alga and diatoms. Here, we provide insights into the significance of ICT excited states following the incorporation of a higher plant carotenoid, β-apo-8′-carotenal, into the carotenoidless light-harvesting 1 (LH1) complex of the purple photosynthetic bacterium Rhodospirillum rubrum strain G9+. β-apo-8′-carotenal generates the ICT excited state in the reconstituted LH1 complex, achieving an efficiency of EET of up to 79%, which exceeds that found in the wild-type LH1 complex.
Commercial silicoaluminophosphate molecular sieves (SAPO-34) received alkali treatment with either NaOH (0.2, 0.01, 0.005, or 0.001 M) or NH 4 OH (0.005 M). Treatment with NaOH (0.005 M) increased the water adsorption initial rate of SAPO-34 by 1.4-fold. The alkali treatment introduced Na + adsorption sites into the SAPO-34. The desorption ratio (adsorption at 30˚C and desorption at 100˚C) was 88.2% higher than the original rate (84.3%). On the other hand, after alkali treatment of SAPO-34 using NH 4 OH (0.005 M), calcination resulted in the highest desorption ratio at 91.3%. When combined with calcination, alkali treatment with NH 4 OH introduced H + adsorption sites into SAPO-34, H + adsorption sites feature low levels of interaction with water, which enhanced the desorption ratio, but decreased the initial adsorption rate. These results indicate that treating commercial SAPO-34 with 0.005 M NaOH enhances both the adsorption and desorption behaviors.
Mercury intrusion porosimetry test was carried out to investigate the quality of thin concrete cover. Specimens with different water-to-cement ratios were prepared and exposed to different environmental conditions. The results show that the pore structure of the cover is coarser than that of the center portion when the cover is insufficient. With thinner cover, the pore structure becomes coarser. With decreasing water-to-cement ratio, the pore structure becomes finer, and the difference in the pore structure between the cover and the center portion becomes smaller. If the cover is insufficient, not only the distance needed for substances to reach the bar becomes shorter, but also the pore structure becomes coarser. At 91 days, the pore structures of outdoor specimens are almost the same as those of indoor specimens although the exposure conditions are different. To investigate the applicability of the air permeability test and electric resistivity test to evaluate the cover quality when the cover is insufficient, specimens with different water-to-cement ratios and cover depths were prepared. A combination of the air permeability test and electric resistivity test roughly pointed out the poor quality of the insufficient concrete cover and is a useful technique to evaluate the concrete cover in real structures.
The excitation energy transfer (EET) from carotenoid to bacteriochlorophyll a (Bchl a) has a significant impact in determining the overall efficiency of utilization of the incident solar spectrum of the primary process of bacterial photosynthesis. This can be enhanced when the carotenoid has intramolecular charge-transfer (ICT) character, such as in the light-harvesting systems in marine alga and diatoms. This study provides new insights into the significance of the ICT excited states following incorporation of a higher plant carotenoid, β-apo-8'-carotenal, into the carotenoidless LH1 system from the purple photosynthetic bacterium, Rhodospirillum rubrum strain G9+. β-apo-8'-carotenal generates two types of the ICT excited state in the reconstituted LH1 complex there by achieving an efficiency of EET that exceeds that found in the wild-type LH1 complex. The present study demonstrates a strategy of how to go beyond the EET efficiency from carotenoid to Bchl a, which has evolved in the bacterial light-harvesting systems.
Cis isomers of carotenoids play important roles in light harvesting and photoprotection in photosynthetic bacteria, such as the reaction center in purple bacteria and the photosynthetic apparatus in cyanobacteria. Carotenoids containing carbonyl groups are involved in efficient energy transfer to chlorophyll in light-harvesting complexes, and their intramolecular charge–transfer (ICT) excited states are known to be important for this process. Previous studies, using ultrafast laser spectroscopy, have focused on the central-cis isomer of carbonyl-containing carotenoids, revealing that the ICT excited state is stabilized in polar environments. However, the relationship between the cis isomer structure and the ICT excited state has remained unresolved. In this study, we performed steady-state absorption and femtosecond time-resolved absorption spectroscopy on nine geometric isomers (7-cis, 9-cis, 13-cis, 15-cis, 13′-cis, 9,13′-cis, 9,13-cis, 13,13′-cis, and all-trans) of β-apo-8′-carotenal, whose structures are well-defined, and discovered correlations between the decay rate constant of the S1 excited state and the S0−S1 energy gap, as well as between the position of the cis-bend and the degree of stabilization of the ICT excited state. Our results demonstrate that the ICT excited state is stabilized in polar environments in cis isomers of carbonyl-containing carotenoids and suggest that the position of the cis-bend plays an important role in the stabilization of the excited state.
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