& Chromophores Light-Harvesting Three-Chromophore Systems Based on Biphenyl- Bridged Periodic Mesoporous Organosilica Lyubov Grçsch, Young Joo Lee, Frank Hoffmann, and Michael Frçba* [a] Abstract: Three-chromophore systems with light-harvesting behavior were prepared, which are based on periodic meso- porous organosilica (PMO) with crystal-like ordered structure. The organic bridges of biphenyl-PMO in the pore walls act as donors and two types of dye are incorporated in the one-dimensional channels. Consecutive two-step-Fçrster res- onance energy transfer is observed from the biphenyl moiet- ies to mediators (diethyl-aminocoumarin or aminoacridone), followed by energy transfer from mediators to acceptors (dibenzothiacarbocyanine, indodicarbocyanine, sulforhod- amine G). High energy-transfer efficiencies ranging from 70 to 80% are obtained for two-step-FRET, indicating that the mesochannel structure with one-dimensional ordering pro- vides spatial arrangement of chromophore pairs for an effi- cient direct energy transfer. The emission wavelength can be tuned by a choice of acceptor dye: 477 nm (diethylamino- coumarin), 519 nm (aminoacridone), 567 nm (sulforhod- amine G), 630 nm (dibenzothiacarbocyanine), and 692 nm (indodicarbocyanine). Introduction Light harvesting, the absorption of the incident light by chro- mophores, has attracted increasing attention for applications as photovoltaic devices, photocatalysts and light-emitting devi- ces. Most of the research up to now has been focused on de- veloping materials that absorb as many photons as possible at the broadest range of wavelength as possible. In recent years, utilization of Fçrster resonance energy transfer (FRET) [1–3] in complex arrays of molecules [4–10] has become a topic of studies because light energy absorbed by donor chromophores can be transferred to acceptor chromophores through FRET, result- ing in shift of emission wavelength. FRET plays a decisive role in light harvesting in various photosystems of algae, land plants, and of bacteria with photosynthetic ability. In spite of the tremendous variety of protein structure and diversity of pigments existing in nature, their light-harvesting antenna ex- hibit high energy-transfer efficiency by adapting various schemes. The association of different pigments, which absorbs light at a broad range of wavelength and channels, collect energy together to one reaction center and enhance the effi- ciency of light absorption. The incorporation of a large amount of the absorbing pigments in one protein unity enhance the efficiency of energy transfer. [4] Different alignment of devices in the light-harvesting complexes cause an alteration in the absorption wavelength range and consequently in the energy transfer. [4] Traditional optoelectronic materials are based on inorganic semiconductors. The biomimetic materials including organic polymers, [11, 12] dendrimers, [13–15] clays, [16–18] hybrid organic–inor- ganic materials [19, 20] and organic–inorganic nanostructured semiconductor materials [21, 22] with light-harvesting behaviors have great potential to find an application in the optoelectron- ics. The photoactive porous materials, such as mesoporous silica materials, periodic mesoporous organosilicas (PMOs), [23–33] metal–organic frameworks (MOFs), [34–36] and zeolites [37–39] provide promising approaches as efficient light-harvesting antenna due to their versatile macroscopic organization. In particular, PMOs [40] exhibit several advantages, which make these materials especially attractive. The silica framework of PMOs provides thermal, mechanical, and chemical stability. A steric separation between donor and acceptor pigments found in the nature can be achieved by designing the structural or- ganization. [18] Donors, which absorb the light energy, can be placed in the pore walls as organic bridges, whereas acceptors, which collect the energy from donors, can be placed in the pores. The high surface area of these materials offers a possibili- ty to insert a large amount of chromophores inside the pores without aggregation. The pore size of PMOs (typically 2.0– 8.0 nm) are in the range of the optimal distance for efficient FRET (up to 8.0 nm). In addition, the emission wavelength of the materials can be tuned by incorporating a variety of chro- mophores into the pores. PMOs with crystal-like pore walls [40] are especially interesting because of the large amount of the densely packed photoactive organic bridges in the pore walls. The alignment of the photoactive moieties enhances the light absorption and the transfer of the excitation energy. The classical two-chromophore–FRET systems, which consist of one type of donor and one type of acceptor, can be extend- ed to the systems containing three or more chromophores, [a] Dr. L. Grçsch, Dr. Y. J. Lee, Dr. F. Hoffmann, Prof. Dr. M. Frçba University of Hamburg, Institute of Inorganic Chemistry Martin-Luther-King-Platz 6, 20146 Hamburg (Germany) E-mail : froeba@chemie.uni-hamburg.de Supporting information for this article is available on the WWW under http ://dx.doi.org/10.1002/chem.201403393. Chem. Eur. J. 2014, 20, 1 – 17  2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1 && These are not the final page numbers! ÞÞ Full Paper DOI: 10.1002/chem.201403393