Ultrafast Energy Transfer in Artificial Antenna Molecule Measured by Transient Fluorescence Spectroscopy

We have reported previously the ultrafast energy transfer process with a time constant of 0.8 ps from a monomeric to a dimeric subunit within a perylenetetracarboxylic diimide trimer, which was derived indirectly from a model fitting into the transient absorption experimental data. Here we present a direct ultrafast fluorescence quenching measurement by employing fs time-resolved transient fluorescence spectroscopy based on noncollinear optical parametric amplification technique. The rapid decay of the monomer＇s emission due to energy transfer was observed directly with a time constant of about 0.82 ps, in good agreement with the previous result.

Solvent-Induced Symmetry-Breaking Charge Transfer in an Octupolar Triphenylamine Derivative Resolved with Transient Fluorescence Spectroscopy

The excited-state symmetry-breaking charge transfer (SBCT) dynamics in quadrupolar or octupolar molecules without clear infrared markers is usually hard to be tracked directly. In this work, on the basis of the evolution of instantaneous emission dipole moment obtained by femtosecond transient fluorescence spectroscopy, we presented a real-time characterization of the solvent-induced SBCT dynamics in an octupolar triphenylamine derivative. While the emission dipole moment of the octupolar trimer in weakly polar toluene changes little during the excited-state relaxation, it exhibits a fast reduction in a few picoseconds in strongly polar tetrahydrofuran. In comparison with the uorescence dynamics of dipolar monomer, we deduced that the emitting state of the octupolar trimer in strongly polar solvent, which undergoes solvent-induced structural uctuation, changes from exciton-coupled octupolar to excitation localized dipolar symmetry. In weakly polar solvent, the octupolar symmetry of the trimer is largely preserved during the solvation stabilization.

Spectrum Correction in Study of Solvation Dynamics by Fluorescence Non-collinear Optical Parametric Amplification Spectroscopy

Femtosecond time-resolved fluorescence non-collinear optical parametric amplification spec- troscopy can extract the curve of spectral gain from its parametric superfluorescence. This unique spectrum correction method enables fluorescence non-collinear optical parametric amplification spectroscopy acquiring the genuine transient fluorescence spectrum of the studied system. In this work we employ fluorescence non-collinear optical parametric amplification spectroscopy technique to study the solvation dynamics of DCM dye in ethanol solution, and confirm that genuine solvation correlation function and shift of peak frequency can be derived from transient fluorescence spectra after the spectral gain correction. It demonstrates that fluorescence non-collinear optical parametric amplification spectroscopy can benefit the research fields, which focuses on both fluorescence intensity dynamics and fluorescence spectral shape evolution.

Systemic regulation of photosynthetic function in maize plants at graining stage under a vertically heterogeneous light environment

To cope with a highly heterogeneous light environment,photosynthesis in plants can be regulated systemically.Currently,the majority of studies are carried out with various plants during the vegetative growth period.As the reproductive sink improves photosynthesis,we wondered how photosynthesis is systemically regulated at the reproductive stage under a vertically heterogeneous light environment in the field.Therefore,changes of light intensity within canopy,chlorophyll content,gas exchange,and chlorophyll a fluorescence transient were carefully investigated at the graining stage of maize under various planting densities.In this study,a high planting density of maize drastically reduced the light intensities in the lower canopy,and increased the difference in vertical light distribution within the canopy.With the increase of vertical heterogeneity,chlorophyll content,light-saturated photosynthetic rate and the quantum yield of electron transport in the ear leaf(EL) and the fourth leaf below the ear(FLBE) were decreased gradually,and the ranges of declines in these parameters were larger at FLBE than those at EL.Leaves in the lower canopy were shaded artificially to further test these results.Partial shading(PS) resulted in a vertically heterogeneous light environment and enhanced the differences in photosynthetic characteristics between EL and FLBE.Removing the tassel and top leaves(RTL) not only improved the vertical light distribution within the canopy,but also reduced the differences in photosynthetic characteristics between the two leaves.Taken together,these results demonstrated that maize plants could enhance the vertical heterogeneity of their photosynthetic function to adapt to their light environment;slight changes of the photosynthetic function in EL at the graining stage under a vertically heterogeneous light environment indicated that the systemic regulation of photosynthesis is weak at the graining stage.