Controlling the efficiency of an artificial light-harvesting complex.

Adaptive femtosecond pulse shaping in an evolutionary learning loop is applied to a bioinspired dyad molecule that closely mimics the early-time photophysics of the light-harvesting complex 2 (LH2) photosynthetic antenna complex. Control over the branching ratio between the two competing pathways for energy flow, internal conversion (IC) and energy transfer (ET), is realized. We show that by pulse shaping it is possible to increase independently the relative yield of both channels, ET and IC.

Ultrafast energy transfer dynamics of a bioinspired dyad molecule.

A caroteno-purpurin dyad molecule was studied by steady-state and pump-probe spectroscopies to resolve the excited-state deactivation dynamics of the different energy levels as well as the connecting energy flow pathways and corresponding rate constants. The data were analyzed with a two-step multi-parameter global fitting procedure that makes use of an evolutionary algorithm. We found that following ultrafast excitation of the donor (carotenoid) chromophore to its S2 state, the energy flows via two channels: energy transfer (70%) and internal conversion (30%) with time constants of 54 and 110 fs, respectively.

Low-noise rotating sample holder for ultrafast transient spectroscopy at cryogenic temperatures.

We present the design and testing of a rotating device that fits within a commercial helium cryostat and is capable of providing at 4 K a fresh sample surface for subsequent shots of a 1-10 kHz amplified pulsed laser. We benchmark this rotator in a transient-absorption experiment on molecular switches. After showing that the device introduces only a small amount of additional noise, we demonstrate how the effect of signal degradation due to high fluence is completely resolved.

Effects of digoxin, placebo and ibopamine on exercise tolerance and cardiac rhythm of patients with chronic post-infarct left ventricular failure.

This study compares the effects of digoxin, placebo and ibopamine (SB-7505), the orally active 3,4-diisobutyryl ester of N-methyl-dopamine, on exercise tolerance and cardiac rhythm of 14 patients whose left ventricular heart failure (end-diastolic pressure, 26.3 +/- 5.9 mmHg; ejection fraction, 0.