Photonic antenna system for light harvesting

Table 1 Dye molecules and abbreviations
BP Py z
pTP PyGY z
DPH PyB z
PBOX Ox z
MBOXE Th z
POPOP ResH
DMPOPOP Hydroxy-TEMPO
DSC DMSI z
Fluorenone N-Ethylcarbazole
Naphthalene a
a From ref. 14.
loaded with Py z in such a way that the occupational
probability was always the same, namely p py~0.11. They
were then modified with two Ox z molecules on average at both
ends of each channel. The fluorescence of a thin layer on quartz
was measured at room temperature after specific excitation of
Py z at 460 nm. It shows a strong increase of the Ox z emission
with decreasing crystal length lcyl. The front–back trapping
efficiency increases from 0.33 up to 0.91. This means that in the
300 nm crystals, 91% of the emitted light is due to energy
migration among the Py z molecules and finally transfer to the
luminescent acceptor Ox z . Experiments with crystals in the
size range of 50 nm show a similar behaviour.
A small shift of the Py z maximum, from 525 nm for the
smallest crystals to 530 nm for the largest ones, is observed.
Anthracene a
This wavelength shift may be due to self-absorption and reemission
because the absorption depth increases with increasing
crystal size despite the constant ppy. The maximum of the
Ox z emission remains at 605 nm.
The time evolution of the excitation distribution along the
cylinder axis of this material is of great interest. 1,2,6 We report
theoretical results obtained for a crystal consisting of 90 slabs,
each of which corresponds to the thickness of a site. The
photophysical data of Py z as donor and Ox z as acceptor were
used to calculate the excitation distribution of the donors.
Immediately after excitation all slabs have the same excitation
probability. The excitation distribution is shown after 5, 10, 50
and 100 ps. We observe in Fig. 5a) that the slabs close to the
acceptor layers lose their excitation energy very quickly. The
J. Mater. Chem., 2002, 12, 1–13 3