Syn th esis a n d Op tica l P r op er ties of Un sym m etr ica l Con ju ga ted
Den d r im er s F oca lly An ch or ed w ith P er ylen es in Differ en t
Geom etr ies
Yongchun Pan,† Meng Lu,† Zhonghua Peng,*,† and J oseph S. Melinger‡
Department of Chemistry, University of Missouri-Kansas City, Kansas City, Missouri 64110, and
Naval Research Laboratory, Electronics Science and Technology Division, Code 6812,
Washington, D.C. 20375
pengz@umkc.edu
Received May 21, 2003
Two sets of light-harvesting monodendrons with unsymmetrical conjugated phenylacetylene
branches and perylene cores, one with π-conjugation from the branches to the core and one without,
were synthesized and their photophysical properties were studied by steady-state and time-resolved
spectroscopic methods. These monodendrons show comparably high fluorescence quantum yields
and efficient energy-transfer properties.
In tr od u ction
coefficients. Further, the convergent surface-to-core
branching structure offers the opportunity for fine-tuning
of the electronic state of each segment so that an intrinsic
energy gradient may be built into the dendritic structure,
which serves as the driving force for the directional
energy flow from the branches to the core.9 Such den-
drimers have found applications as light-emitting diodes5
and fluorescence sensors,6 and in other photonic de-
vices.7,8
We have recently reported unsymmetrical conjugated
phenylacetylene (PA) monodendrons.4 The unique branch-
ing structure results in broad absorptions and an intrin-
sic energy gradient toward the core. To evaluate quan-
titatively the energy-transfer efficiency and kinetics, and
to establish structure-property relationship regarding
energy transfer and π-conjugation, a perylene unit serv-
ing as an energy trap has been attached to the focal point
of the monodendrons. Two types of linkages are adopted,
one with perylene directly attached to the monodendrons
so that there is an extended π-conjugation between the
PA dendron and the perylene units, the other with
perylene and the PA monodendrons linked by a benzene
ring at meta positions, which disrupts the conjugation
and thus provides an extra degree of isolation between
the monodendron and the perylene trap. Herein, we
present the detailed synthesis of such perylene-anchored
monodendrons and the comparison of their optical prop-
erties.
Conjugated dendrimers have been extensively studied
in recent years.1 Not only have synthetic methodologies
been well-developed and a number of conjugated den-
drimers been prepared,1-4 their applications as new
molecular electronic and photonic materials have also
been explored.5-8 In particular, conjugated dendrimers
have some unique features which make them attractive
candidates as new synthetic light-harvesting materi-
als.4,9-10 For example, the high density of light-absorbing
dendritic branches results in high molar extinction
* Corresponding author. Phone: 816-235-2288.
† University of Missouri-Kansas City.
‡ Naval Research Laboratory.
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Syn th esis of P er ylen e-An ch or ed Mon od en d r on s.
Chart 1 shows the structures of the unsymmetrical PA
monodendrons anchored with perylenes in direct π-con-
jugation (Gn P er ), while Chart 2 shows the structures
of compounds with two PA dendrons and one perylene
unit linked through the meta positions of a phenyl ring
(2Gn P er ). The labels (a, a′, b, c, etc.) are for 1H NMR
assignments.
10.1021/jo0346858 CCC: $25.00 © 2003 American Chemical Society
Published on Web 08/02/2003
6952
J . Org. Chem. 2003, 68, 6952-6958