DOI: 10.1002/cplu.201200279 The Ugi Four-Component Reaction Route to Photoinducible Electron-Transfer Systems Sarah Bay, [a] Torben Villnow, [b] Gerald Ryseck, [b] Vidisha Rai-Constapel, [c] Peter Gilch, [b] and Thomas J. J. Müller* [a] Among functional organic materials, [1] donor–acceptor (D–A) conjugates have aroused preeminent interest in advanced and future technologies, such as molecular electronics and optoe- lectronics. They constitute key functional units in rectifiers, nonlinear optical materials, [2] and photovoltaic devices. [3] In particular, light-to-current conversion is founded on the princi- ples of photoinduced electron transfer (PET). [4] Besides well-es- tablished electron-donating moieties, such as porphyrins, poly- cyclic aromatic hydrocarbons, perylenediimides, [5] and (oligo)- thiophenes, [6] phenothiazine (PT) derivatives [3b, 7] have become increasingly attractive as electrophores because of their rever- sible and tunable oxidation potentials. On the other hand, full- erene [8] and 9,10-anthraquinone (AQ) derivatives [9] have found application as favorable electron-acceptor units in D–A sys- tems. For instance, PT–acceptor dyads display intramolecular PET, which can be identified readily by quenching of the PT fluorescence. [10] The formation of charge-separated states can be verified by various spectroscopic methods, such as EPR spectroscopy, flash photolysis, or ultrafast transient spectrosco- py. Although combinations of phenothiazines and anthraqui- nones as advantageous D–A pairs based upon peptide scaf- folds [11] and rigid alkynyl-bridged dyads [12] have been proposed, prepared, and studied with respect to PET, a general, facile, and diversity-oriented synthetic approach to D–A systems has remained unexplored so far. Surprisingly, the most elegant syn- thetic approach to these types of functional p-electron systems by multicomponent reactions has never been scouted prior to this work. In particular, the Ugi four-component reaction (4CR), [13] which furnishes the chemically robust a-aminoacyl amide scaffold with high level of diversity, is applied widely in biological and medicinal chemistry [14] but has never been used for the synthesis of functional D–A PET systems before. Herein, we report the first Ugi 4CR route to a PT–AQ-based PET system and its electronic characterization by cyclic voltammetry, steady-state UV/Vis and fluorescence spectroscopy, as well as femtosecond transient absorption spectroscopy for identifica- tion of the desired charge-separated state after light excita- tion. Upon performing the Ugi 4CR with phenothiazinyl methyl ammonium chloride (by liberating the base with potassium hy- droxide), [15] anthraquinone-2-carbaldehyde, acetic acid, and tert-butyl isocyanide in methanol and dichloromethane at room temperature, the PT–AQ dyad 1 is obtained in good yield (Scheme 1). Likewise and for spectroscopic comparison, the Ugi 4CR is also successfully applied to synthesize the ac- ceptor-only reference 3 upon reacting isopropylamine as amino component and the donor-only 2 with acetaldehyde (Scheme 1). For a closer inspection of the electronic properties, the D–A dyad 1 and the references 2 and 3 were studied by steady- state UV/Vis absorption and fluorescence spectroscopy and by cyclic voltammetry. For an estimation of the electron-transfer Scheme 1. Ugi 4CR synthesis of the donor–acceptor conjugate 1 and the ref- erence systems 2 and 3. [a] S. Bay, + Prof. Dr. T. J. J. Müller Institut für Organische Chemie und Makromolekulare Chemie Heinrich-Heine-Universität Düsseldorf Universitätsstraße 1, 40225 Düsseldorf (Germany) E-mail : ThomasJJ.Mueller@uni-duesseldorf.de [b] Dipl.-Chem. T. Villnow, + Dipl.-Phys. G. Ryseck, Prof. Dr. P. Gilch Institut für Physikalische Chemie Heinrich-Heine-Universität Düsseldorf (Germany) [c] Dr. V. Rai-Constapel Institut für Theoretische Chemie und Computerchemie Heinrich-Heine-Universität Düsseldorf (Germany) [ + ] These authors contributed equally to this work. Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cplu.201200279.  2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim ChemPlusChem 2013, 78, 137 – 141 137 CHEMPLUSCHEM COMMUNICATIONS