Contemporary percutaneous treatment of unprotected left main coronary stenoses: initial results from a multicenter registry analysis 1994-1996.

BACKGROUND: Coronary artery bypass surgery (CABG) has been considered the therapy of choice for patients with unprotected left main (ULMT) coronary stenoses. Selected single-center reports suggest that the results of percutaneous intervention may now approach those of CABG. METHODS AND RESULTS: To assess the results of percutaneous ULMT treatment from a wide variety of experienced interventional centers, we requested data on consecutive patients treated after January 1, 1994, from 25 centers. One hundred seven patients were identified who were treated either electively (n=91) or for acute myocardial infarction (n=16). Of patients treated electively, 25% were considered inoperable, and 27% were considered high risk for bypass surgery. Primary treatment included stents (50%), directional atherectomy (24%), and balloon angioplasty (20%). Follow-up was 98.8% complete at 15+/-8 months. Results varied considerably, depending on presentation and treatment. For patient

Exciton Diffusion in Conjugated Polymers: From Fundamental Understanding to Improvement in Photovoltaic Conversion Efficiency

Singlet exciton diffusion plays a central role in the photovoltaic conversion in organic photovoltaics (OPVs). Upon light absorption, singlet excitons are promptly generated in organic materials instead of charge carriers because the dielectric constant (εr) is small (∼3-4), which is in sharp contrast to inorganic and perovskite solar cells. In order to convert to charge carriers, excitons need to diffuse into an interface between electron donor and acceptor materials before deactivating to the ground state. Therefore, fundamental understanding of exciton diffusion dynamics is one of the most important issues to further improve OPVs. We highlight recent leading studies in this field and describe several approaches for efficient exciton harvesting at the interface in OPVs

One-Dimensional Singlet Exciton Diffusion in Poly(3-hexylthiophene) Crystalline Domains

Singlet exciton dynamics in crystalline domains of regioregular poly­(3-hexylthiophene) (P3HT) films was studied by transient absorption spectroscopy. Upon the selective excitation of crystalline P3HT at the absorption edge, no red shift of the singlet exciton band was observed with an elapse of time, suggesting singlet exciton dynamics in relatively homogeneous P3HT crystalline domains without downhill relaxation in the energetic disorder. Even under such selective excitation conditions, the annihilation rate coefficient γ­(<i>t</i>) was still dependent on time, γ­(<i>t</i>) ∝ <i>t</i>^–1/2, which is attributed to anisotropic exciton diffusion in P3HT crystalline domains. From the annihilation rate coefficient, the singlet exciton diffusion coefficient <i>D</i> and exciton diffusion length <i>L</i>_D in the crystalline domains were evaluated to be 7.9 × 10^–3 cm² s^–1 and 20 nm, respectively. The origin of the time-dependent exciton dynamics is discussed in terms of dimensionality

Singlet Fission in Poly(9,9′-di- n

The dynamics of singlet fission in poly(9, 9′-di-n-octylfluorene) (PFO) films was studied by transient absorption spectroscopy. Under a high excitation intensity, triplet excitons were rapidly interconverted from singlet excitons on a picosecond time stage. From the excitation intensity dependence of the generation yield, the rapid triplet exciton formation is attributed to the singlet fission from a higher singlet excited state Sn formed by the singlet–singlet annihilation (singlet fusion followed by singlet fission). The singlet fission from the Sn state was about 2 times more efficient in amorphous PFO films than in ordered β-PFO films, in which the conjugated main chains are planarly extended and aligned. On the other hand, about a half of triplet pairs were deactivated in the amorphous PFO film through the triplet–triplet annihilation with a time constant of 1.7 ns, while no triplet pair decay was observed in the β-PFO film. As a result, the overall triplet generation yield was comparable in these films. The decrease in the fission efficiency in the β-PFO is discussed in terms of the presence of another relaxation pathway from the Sn state. The efficiency of triplet pair dissociation is discussed in terms of the triplet exciton diffusion