Chemistry Reference
In-Depth Information
FIGURE 12.19
(a) Defocused wide-field images of the same sample area but different
emission wavelengths, showing the emission and orientation of TDI (left) and PMI chromo-
phores (right). (b) Simultaneous emission from the dendrimer chromophores: each row
represents a different molecule. On the left the acceptor emission and fitted orientational
pattern are shown, while on the right side the donor emission and fitted pattern are shown. The
patterns indicate that the donor and acceptor chromophores are oriented perpendicular to one
another. Copyright fromRef. [131]. (See the color version of this figure in Color Plates section.)
PMI annihilation or by singlet PMI-singlet TDI annihilation, which leads to the
existence of only one excited chromophore, the acceptor. After photobleaching of a
number of donors, unfavorably oriented donors can become “isolated.” When these
donors are excited, theywill not undergo FRETnorwill they annihilatewith the excited
acceptor molecule, eventually populated via other donors, but relax to the ground state
by emission of fluorescence. Thus, the simultaneous donor-acceptor emission in the
dendritic systems arisesmainly fromunfavorably oriented donormolecules and only to
a minor extent from an exciton blockade resulting from multiple excitations.
A system devised for cascade energy transfer is the third-generation globular
polyphenylene dendrimer compound
13
(see Figure 12.20) bearing a TDI
