Researchers in the Papanikolas Group, report in Journal of Physical Chemistry A, how images of second harmonic generation (SHG) in needle-shaped ZnO rods obtained from individual structures show areas of enhanced second harmonic intensity along the longitudinal axis of the rod that are periodically distributed and symmetrically situated relative to the rod midpoint.
The spatial modulation is a direct consequence of the fundamental optical field coupling into standing wave resonator modes of the ZnO structure, leading to an enhanced backscattered second harmonic condition that cannot be achieved in bulk ZnO. A more complicated second harmonic image is observed when excitation is below the band gap, which is attributed to whispering gallery modes. This physical phenomenon, which extends beyond just ZnO to many other optical materials, could pave the way to new applications that exploit the nonlinear optical properties of individual structures.
In a collaboration between researchers in the Papanikolas Group and the Meyer Group, results of CW and lifetime emission studies have been used to demonstrate facile intra-strand energy transfer in the derivatized polystyrene polymer
[PS-4-CH2CH2NHC(O)-(RuII(4,4'-(CONEt2)2bpy)2)17
(OsII(bpy)2))3](PF6)40 in four rigid media: frozen 5:4 (v:v) propionitrile:butyronitrile solutions at 77 K, polymethyl-methacrylate (PMMA) and polyethylene glycol-dimethacrylate (PEG-DMA) films, and silica xerogel monoliths at room temperature.
Continued rapid energy transfer in rigid media is in contrast to electron transfer which is inhibited. This can be explained by energy transfer theory and is due to a decrease in the energy transfer barrier because of the frozen nature of the medium. The abbreviation used for the polymer defines the chemical link to the polystyrene backbone and gives the extent of loading out of 20 available sites. This was an important observation since one goal of the work with polymers was to use them as light absorbing antenna in artificial photosynthesis applications. As assemblies, the multi-site polymers were massive light absorbers but at isolated, electronically weakly coupled sites. In order to use the excited state energy for energy conversion at a remote site requires facile intra-strand energy migration and transfer on the lifetime of the polymer-bound excited states.