illustrated in Sect. 2.2. Although the observation of EET qualitatively provided
clear evidence for the formation of such complexes, more detailed studies have
revealed that Fo ¨rster theory seems to give a reasonable description of the process.
Besides QD/dye hybrids, well-defined QD oligomers have been prepared by a novel
route involving ultracentrifugation as the final separation step, paving the way
towards QD molecules. In Sect. 2.3, it is shown that rylene dyes also can serve
as energy donors and/or acceptors in hybrid constructs with light-harvesting
complexes (LHCII) from green plants. Eventually, LHCII in such constructs may
sensitize electron injection into a semiconductor layer via an acceptor dye. The use
of recombinant versions of LHCII afforded the incorporation of anchors such as
hexahistidine tags for specific interaction with QDs, in which case complex formation was again signaled by EET. Another way of arranging emitters is presented in
Sect. 2.4, which describes the use of cholesteric phases for the formation of helical
superstructures of dye molecules. Lasing was observed in free-standing cholesteric
films after introduction of the emitters. Section 3 is devoted to the visualization of
EET between individual molecules in donor–acceptor dyads. Time- and frequencyresolved single-molecule techniques have been employed to address the
mechanism of EET and have allowed quantification of deviations from a Fo ¨rster
description. Successful attempts to reverse the energy flow in individual aggregates
demonstrated how aggregate function could be modified. The turning on and off of
EET could be used to read out the spin state of a single molecule. The chapter closes
with theoretical efforts (Sect. 4) on the description of photophysical parameters
and processes. Quantum chemical ab-initio methods have been applied for the
determination of electronic transition energies, the vibronic structure of emission
spectra and electronic coupling strength between molecules. Indeed, the stringent
combination of synthetic chemistry, SMS and quantum chemistry has delivered
quantitative insights into electronic coupling in molecular assemblies.
2 Preparation and Photophysical Properties
2.1 Multichromophoric Systems Tailored for Energy
Transfer Applications
2.1.1 Linear and Kinked Donor–Acceptor Dyads
PDI–TDI Dyads
In 2004, the first work was reported directed toward single-pair electronic EET in a
dyad built from perylene diimide (PDI) as donor, terrylene diimide (TDI) as
acceptor and a p-terphenyl spacer (dyad 1, Fig. 1) as bridging group [1]. Since
then, several more single-molecule as well as computational studies on this
compound have been carried out to investigate the prevailing energy transfer
Optical Properties of Assemblies of Molecules and Nanoparticles
63
clear evidence for the formation of such complexes, more detailed studies have
revealed that Fo ¨rster theory seems to give a reasonable description of the process.
Besides QD/dye hybrids, well-defined QD oligomers have been prepared by a novel
route involving ultracentrifugation as the final separation step, paving the way
towards QD molecules. In Sect. 2.3, it is shown that rylene dyes also can serve
as energy donors and/or acceptors in hybrid constructs with light-harvesting
complexes (LHCII) from green plants. Eventually, LHCII in such constructs may
sensitize electron injection into a semiconductor layer via an acceptor dye. The use
of recombinant versions of LHCII afforded the incorporation of anchors such as
hexahistidine tags for specific interaction with QDs, in which case complex formation was again signaled by EET. Another way of arranging emitters is presented in
Sect. 2.4, which describes the use of cholesteric phases for the formation of helical
superstructures of dye molecules. Lasing was observed in free-standing cholesteric
films after introduction of the emitters. Section 3 is devoted to the visualization of
EET between individual molecules in donor–acceptor dyads. Time- and frequencyresolved single-molecule techniques have been employed to address the
mechanism of EET and have allowed quantification of deviations from a Fo ¨rster
description. Successful attempts to reverse the energy flow in individual aggregates
demonstrated how aggregate function could be modified. The turning on and off of
EET could be used to read out the spin state of a single molecule. The chapter closes
with theoretical efforts (Sect. 4) on the description of photophysical parameters
and processes. Quantum chemical ab-initio methods have been applied for the
determination of electronic transition energies, the vibronic structure of emission
spectra and electronic coupling strength between molecules. Indeed, the stringent
combination of synthetic chemistry, SMS and quantum chemistry has delivered
quantitative insights into electronic coupling in molecular assemblies.
2 Preparation and Photophysical Properties
2.1 Multichromophoric Systems Tailored for Energy
Transfer Applications
2.1.1 Linear and Kinked Donor–Acceptor Dyads
PDI–TDI Dyads
In 2004, the first work was reported directed toward single-pair electronic EET in a
dyad built from perylene diimide (PDI) as donor, terrylene diimide (TDI) as
acceptor and a p-terphenyl spacer (dyad 1, Fig. 1) as bridging group [1]. Since
then, several more single-molecule as well as computational studies on this
compound have been carried out to investigate the prevailing energy transfer
Optical Properties of Assemblies of Molecules and Nanoparticles
63