Hung-g Chen

The mediated excitation energy transfer: Effects of bridge polarizability.

The observation of bridge-mediated excitation energy transfer (EET) has raised questions on the physical origin of such an effect. In this work, we studied the effect of bridge fragments in the Coulomb coupling, the major contribution to the electronic coupling in an EET process. For a series of ortho-phenyleneethynylene oligomers spaced donor-acceptors, we found that a large influence of the bridge fragment in EET coupling is through changes in the Coulomb couplings. Both enhancement and screening effects of the bridge were observed as the EET rates were modified by a factor of 0.3-23 with an intervening bridge in our calculations. The dependency of EET couplings on the orientation of transition dipoles of the donor and acceptor from quantum mechanical computations is very similar to that of a simple classical dielectric model. Our work shows that the bridge fragments can modify the Coulomb coupling with their polarizability by providing an optical dielectric medium between the donor and acceptor. In particular, when the transition dipoles of the donor and acceptor were longitudinal to a polarizable bridge, the EET rates were enhanced by one order of magnitude, as compared to the values of through-space models. Our results offer important insights into the design of efficient energy transfer systems.

Using brachial-ankle pulse wave velocity to associate arterial stiffness with cardiovascular risks

BACKGROUND AND AIMS This study aimed to elucidate the relationship between brachial-ankle pulse wave velocity (baPWV) and conventional cardiovascular risk factors. METHODS AND RESULTS A total of 192 subjects with low to intermediate risk was enrolled in a cardiovascular evaluation program. A multiple regression model was built to find significant cardiovascular biomarkers for predicting baPWV. A logistic regression model was developed to associate baPWV and other biomarkers with the risk of cardiac diastolic dysfunction. A total of 123 men (mean age: 52.6+/-12.0) and 69 women (mean age: 51.7+/-10.4) was included. Age, blood pressure, C-reactive protein, serum homocysteine, heart rate, and blood urea nitrogen were positively predictive of increased pulse wave velocity. In turn, baPWV increased the risk (odds ratio: 1.257 for each m/s, 95% CI: 1.105 approximately 1.430, p<0.001) and high-density lipoprotein decreased the risk for cardiac diastolic dysfunction (0.962 for each mg/dl, 95% CI: 0.925 approximately 1.000, p=0.05). The correlation between baPWV and Framingham 10-year risk was moderate (men: r=0.306, p=0.002; women r=0.548, p<0.001). CONCLUSION The results suggest that baPWV is a composite risk factor for early atherosclerotic change and a predictor for the development of diastolic dysfunction and long-term cardiovascular risk.

Platinum(II)–porphyrin as a sensitizer for visible-light driven water oxidation in neutral phosphate buffer

A water-soluble Pt(II)–porphyrin with a high potential for one-electron oxidation (∼1.42 V vs. NHE) proves very suitable for visible-light driven water oxidation in neutral phosphate buffer solution in combination with a variety of water oxidation catalysts (WOCs). Two homogeneous WOCs (iridium(N-heterocyclic carbene) and Co4O4–cubane complexes) and two heterogeneous WOCs (IrOx·nH2O and Co3O4 nanoparticles) were investigated, with sodium persulfate (Na2S2O8) as a sacrificial electron acceptor. Under neutral buffer conditions, the Pt(II)–porphyrin shows higher stability than the commonly used photosensitizer [Ru(bpy)3]2+, and therefore represents a good alternative photosensitizer to be used in the evaluation of light driven WOCs.

Association of intraocular pressure with the metabolic syndrome and novel cardiometabolic risk factors

Background and aimsThis study aimed to investigate the association of intraocular pressure (IOP) with the metabolic syndrome and other emerging cardiometabolic risk factors.MethodsA total of 1112 participants undergoing a health check-up in a community hospital were recruited. All participants underwent ophthalmological examination including IOP measurement.ResultsParticipants with metabolic syndrome had significantly higher IOP than those without metabolic syndrome (mean IOP±SD: 15.07±2.74 vs14.29±2.72 mm Hg, P=2 × 10−4). Each additional component of the metabolic syndrome was associated with a mean increase in IOP of 0.33 mm Hg (95% confidence interval: 0.18–0.48, trend P<0.0001). Other insulin resistance-related features, including hepatic steatosis, increased left ventricular mass, and proteinuria, were also associated with IOP (P<0.0001, 0.002, and 0.01, respectively). However, we did not find significant association of plasma apolipoprotein A, apolipoprotein B1, homocysteine, or highly sensitive C-reactive protein levels with IOP. IOP was also not associated with measures of subclinical atherosclerosis including brachial–ankle pulse wave velocity, ankle–brachial index, and vertebral artery flow.ConclusionMetabolic syndrome and other insulin resistance-related features, including hepatic steatosis, increased left ventricular mass, and proteinuria, are strongly associated with IOP.

A noble-metal-free system for photodriven catalytic proton reduction.

Who needs the nobles? Ideally, devices to harvest solar energy into fuels would, in addition to having very high turnover numbers, make use of earth-abundant materials. In this Highlight we focus on a recent example in which a copper-based photosensitizer is used, in combination with an iron-based catalyst for light-driven proton reduction.

Theoretical characterization of photoinduced electron transfer in rigidly linked donor–acceptor molecules: the fragment charge difference and the generalized Mulliken–Hush schemes

We calculate the electron transfer (ET) rates for a series of heptacyclo[6.6.0.02,6.03,13.014,11.05,9.010,14]-tetradecane (HCTD) linked donor–acceptor molecules. The electronic coupling factor was calculated by the fragment charge difference (FCD) [19] and the generalized Mulliken–Hush (GMH) schemes [20]. We found that the FCD is less prone to problems commonly seen in the GMH scheme, especially when the coupling values are small. For a 3-state case where the charge transfer (CT) state is coupled with two different locally excited (LE) states, we tested with the 3-state approach for the GMH scheme [30], and found that it works well with the FCD scheme. A simplified direct diagonalization based on Rusts 3-state scheme was also proposed and tested. This simplified scheme does not require a manual assignment of the states, and it yields coupling values that are largely similar to those from the full Rusts approach. The overall electron transfer (ET) coupling rates were also calculated.

Robust Benzo[g, h, i ]perylenetriimide Dye-Sensitized Electrodes in Air-Saturated Aqueous Buffer Solution

Highly electron deficient benzo[ghi]perylenetriimide (BPTI) chromophores were persistently anchored to a metal oxide electrode surface and reversible formation of their radical anions was shown in air-saturated aqueous buffer solution. Our results show a very low reaction-rate constant of BPTI(.-) with O2 (k=1.92 ± 0.05 × 10(-2) s(-1)). BPTI is a robust chromophore that can be used as the electron acceptor in molecule-based artificial photosynthetic devices for direct water splitting in aqueous phase.

Highly soluble benzo[ghi]perylenetriimide derivatives: stable and air-insensitive electron acceptors for artificial photosynthesis

A series of new benzo[ghi]perylenetriimide (BPTI) derivatives has been synthesized and characterized. These remarkably soluble BPTI derivatives show strong optical absorption in the range of λ=300–500 nm and have a high triplet-state energy of 1.67 eV. A cyanophenyl substituent renders BPTI such a strong electron acceptor (Ered=−0.11 V vs. the normal hydrogen electrode) that electron-trapping reactions with O2 and H2O do not occur. The BPTI radical anion on a fluorine-doped tin oxide|TiO2 electrode is persistent up to tens of seconds (t1/2=39 s) in air-saturated buffer solution. As a result of favorable packing, theoretical electron mobilities (10−2∼10−1 cm2 V−1 s−1) are high and similar to the experimental values observed for perylene diimide and C60 derivatives. Our studies show the potential of the cyanophenyl-modified BPTI compounds as electron acceptors in devices for artificial photosynthesis in water splitting that are also very promising nonfullerene electron-transport materials for organic solar cells.

Ultrafast Charge and Triplet State Formation in Diketopyrrolopyrrole Low Band Gap Polymer/Fullerene Blends: Influence of Nanoscale Morphology of Organic Photovoltaic Materials on Charge Recombination to the Triplet State

Femtosecond transient absorption spectroscopy of thin films of two types of morphologies of diketopyrrolopyrrole low band gap polymer/fullerene-adduct blends is presented and indicates triplet state formation by charge recombination, an important loss channel in organic photovoltaic materials. At low laser fluence (approaching solar intensity) charge formation characterized by a 1350 nm band (in ~250 fs) dominates in the two PDPP-PCBM blends with different nanoscale morphologies and these charges recombine to form a local polymer-based triplet state on the sub-ns timescale (in ~300 and ~900 ps) indicated by an 1100 nm absorption band. The rate of triplet state formation is influenced by the morphology. The slower rate of charge recombination to the triplet state (in ~900 ps) belongs to a morphology that results in a higher power conversion efficiency in the corresponding device. Nanoscale morphology not only influences interfacial area and conduction of holes and electrons but also influences the mechanism of intersystem crossing (ISC). We present a model that correlates morphology to the exchange integral and fast and slow mechanisms for ISC (SOCT-ISC and H-HFI-ISC). For the pristine polymer, a flat and unstructured singlet-singlet absorption spectrum (between 900 and 1400 nm) and a very minor triplet state formation (5%) are observed at low laser fluence.

The 3 D Structure of Twisted Benzo[ghi]perylene-Triimide Dimer as a Non-Fullerene Acceptor for Inverted Perovskite Solar Cells

Here, we introduced benzo[ghi]perylenetriimide (BPTI) derivatives including monomer and twisted dimer (t-BPTI) as an alternative electron-transport layer (ETL) material to replace the commonly used PC61 BM in inverted planar heterojunction perovskite solar cells (PSCs). Moreover, the double ETL was applied in our PSCs with structure of glass/ITO/PEDOT:PSS/perovskite/BPTI/C60 or PDI-C4/BCP/Al. The use of a double ETL structure can effectively eliminate the leakage current. The devices with the t-BPTI/C60 double ETL yield an average power conversion efficiency of 10.73 % and a maximum efficiency of 11.63 %. The device based on the complete non-fullerene electron acceptors of t-BPTI/PDI-C4 as double ETL achieved maximum efficiency of 10.0 %. Moreover, it was found that the utilization of alloy t-BPTI+BPTI as ETL can effectively reduce the hysteresis effect of PSCs. The results suggest that BPTI-based electron-transport materials are potential alternatives for widely used fullerene acceptors in PSCs.