Self-Assembled Monolayers of Photo- Electroactive Organic Molecules: Photoinduced Electron Transfer as Sensing Mechanism Nikolai V. Tkachenko, Alexander Efimov, Helge Lemmetyinen Department of Chemistry and Bioengineering Tampere University of Technology PO Box 541, 33101 Tampere, Finland Email: nikolai.tkachenko@tut.fi Abstract—In this paper, the photoinduced electron transfer in the monomolecular layers of porphyrin-fullerene and phthalocyanine-fullerene dyads self-assembled on an ITO electrode have been presented. The photocurrent and photovoltage responses can be manipulated by chemical engineering of the layer, e.g. changing the order of the donor and acceptor units. Since the efficiency of the photoinduced electron transfer depends strongly on the layer environment, such structures can be used for sensor applications. I.INTRODUCTION A great variety of organic donor-acceptor (DA) dyads have been developed and thoroughly studied recently [1]. The photo-excitation of such molecules results in a charge transfer from the donor to the acceptor in a process similar to the electron transfer in natural photosynthetic reaction centers. The most widely discussed application areas of the DA compounds are photovoltaic devices and solar cells [2]. However, sensor applications of the organized DA molecular structures are feasible too. A DA dyad, consisting of a porphyrinoid donor and a fullerene acceptor moieties can form a monolayer with uniform molecular orientation on an semiconductor electrode, and under light illumination an electron transfer (ET) takes place in direction to or from the electrode depending on the orientation of the dyads [3,4]. The ET efficiency changes when the environment changes, and can be measured by detecting photocurrent or photovoltage responses of the samples. That is, a DA monolayer can sens surrounding medium and generate electric signal accordingly. II.RESULTS AND DISCUSSION A. Donor-Acceptor Compounds Two main goals for the chemical engineering of new DA compounds were (1) an efficient photoinduced charge transfer, and (2) a suitability to form a well ordered molecular films. The first goal was achieved by using well known donor and acceptor molecules as building blocks for new compounds. A few examples are presented in Fig. 1 [5-7]. Fullerene C60 was used as the electron acceptor for all these dyads. The donor units were porphyrin and phthalocyanine derivatives. To solve the second problem the dyads were decorated by peripheral groups enforcing monolayer self-assembling under certain conditions. PaF PbF DHD6ee O O O O O O O O O N H N NH N O Ph(tBu) 2 OH O H O O O O O O O O N H N N N NH N N N O O TBD6th PcF Fig. 1. Structures of donor-acceptor compounds and their notations. B. Photochemistry in Liquide Phase Photoinduced electron transfer properties of new compounds are first studied in solution. The photoreactions N N H N NH N O O O N N H N NH N O OH O O O O O N H N NH N O O PhOC 2 H 4 OH O O O O O OH 1-4244-2581-5/08/$20.00 ©2008 IEEE 1509 IEEE SENSORS 2008 Conference