Förster‐Type Energy Transfer along a Specified Axis

Abstract

Förster transfer of electronic excitation energy in 3D [1][2][3] and 2D [4,5] systems has been studied in many laboratories. Kuhn extended the Förster theory of long-range energy transfer in 3D systems to 2D and 1D systems.[6] The theory of the time dependence of this process in 1D and 2D cases was studied by Hauser et al. [7] and later extended to fractal dimensions by several groups. [8,9] Nevertheless, only little experimental evidence has been published to prove 1D energy transfer. In the strict sense, one-dimensionality can be understood as a transport along a line or at least along an isolated file. However, one-dimensionality in the 3D space of an object of, for example, cylindrical morphology can also mean that the nett transport of the individual transfer steps goes along the c axis of the cylinder, that is, along a well-defined axis. We call this quasi-1D to avoid any confusion.One way to try to realize the conditions in which quasi-1D transport of excitation energy should be favored is by using dye molecules in a crystalline host that consists of 1D channels. Panchromatic chromophore mixtures in an AlPO 4 -5 molecular sieve show interesting luminescence properties. [10] We have shown that zeolite L, with its 1D channels, is a very versatile material with which to build artificial host-guest antenna systems.[11] The channels are occupied by energy-transporting dyes (donors, D) and energy-trapping dyes (acceptors, A); strongly luminescent dyes are usually selected. The energy-transfer process that occurs when an excited donor transports its excitation energy to an unexcited acceptor proceeds with a Förster-type mechanism and its rate constant k DA can be expressed according to Equation (1), in which f D and t D are thefluorescence quantum yield and lifetime, respectively, of the donor, J DA is the spectral overlap integral between the donor emission and the acceptor absorption spectra, k DA describes the relative orientation of the electronic transition moments, and R DA is the distance between D and A. R DA has a strong effect on the energy-transfer rate constant. It can be tuned, for example, by varying the loading of the dye molecules [12] , which changes the overall dye-dye distance. Another elegant way to study the distance dependence of the transfer of excitation energy is to introduce a spacer molecule between the donors and the acceptors to separate them locally, as illustrated in Figure 1. To realize this introduction, a defined quantity of acceptor molecules was first incorporated into the channels of zeolite L. In the second step, different quantities of spacer molecules were incorporated into the channels that already contained acceptor dyes, thus forming spacer layers of different thicknesses. In the third step, the same quantity of donor dyes was always added. As the conditions are such that the dyes cannot glide past each other, the crystal is divided into compartments in which the density of one dye is dominant. By selectively exciting the donor, the behavior of the excitation energy can ...

Designing Dye–Nanochannel Antenna Hybrid Materials for Light Harvesting, Transport and Trapping

“…The loading p with HY3G, as determined by dissolving and analyzing the sample as reported in ref. [40], was 0.5, assuming that it occupies 3 u.c., and that of Ox + , which occupies 2 u.c., was 0.01. This means that we have on average about 100 HY3G molecules in each channel and on average 1.5 Ox + molecules at both ends.…”

“…The rate equation for FRET by following the arguments given in the original work of Fçrster [24] and the description of exciton coupling based on Davydov's theory [27] have been extremely useful for designing and understanding organized systems based on nanochannel materials. [15,[36][37][38][39][40] We restrict the discussion to one photon processes taking place under ambient temperature conditions. This means that processes in which two or more electronically excited molecules interact with each other-leading to phenomena such as annihilation processes, super radiance, lasing and others; but also very low temperature situations where shallow traps may be important -are not discussed.…”

“…Cross-talking between molecules located in neighboring channels is, of course, possible and has been investigated theoretically and experimentally, to some extent. [36,[39][40][41][42] We do not investigate this further here, despite of the fact that it can be important. In order to realize noncentrosymmetric filling of the channels, one side of the channel opening must be blocked while keeping the other side open.…”

Dye‐Modified Nanochannel Materials for Photoelectronic and Optical Devices

“…[2][3][4] Zeolite L consists of strictly parallel channels arranged in a hexagonal framework as shown in Figure 1. Its stoichiometry is [M] + 9 A C H T U N G T R E N N U N G (SiO 2 ) 27 ]·n H 2 O, in which M + are monovalent ions compensating the negative charge resulting from the aluminium atoms and n is 21 in fully hydrated materials, and 16 at about 22 % relative humidity.…”

Zeolithkristalle: Morphologie und Katalyse

“…[15] Bezüglich der räumlichen Auflösung ist die IR-Mikroskopie der OM wellenlängenbedingt zwar unterlegen (typischerweise 20 20 mm 2 ), doch weil Synchrotronstrahlung um 100-bis 1000-mal intensiver ist als Strahlung aus üblichen IR-Lichtquellen, wird eine räumliche Auflösung nahe der Beugungsgrenze erzielt (gewöhnlich unter 5 [17][18][19] Alles in allem sieht die Zeolithforschung einer prächtigen Zukunft entgegen.…”