This current project focuses on synthetic functional systems that are relevant for the materials sciences.  The general objective is to develop synthetic methods to build functional architectures of highest possible sophistication.  This is important because in nature, significant function is achieved by exceptionally complex architectures, and no one really knows what organic materials we would get if we could construct complex functional systems with similar precision.  This question is open because the synthetic methods to construct multicomponent architectures with high precision are simply missing.  In this project, we hope to help changing this situation and make sophisticated multicomponent architectures as accessible for the synthetic organic chemist as small molecules are today.

With regard to function, we decided to focus on multicomponent architectures that convert photonic energy into chemical or electrical energy because this is of interest with regard to basic science as well as applications toward optoelectronic devices.  Naturally, our emphasis is on conceptual innovation (rather than on device engineering).  One motif of current interest are co-axial molecular-level charge-transporting channels with oriented multicomponent redox gradients in each channel to drive holes and electrons away from each other before they can recombine (so-called OMARG SHJs).  This is as in biological photosystems, requires sophisticated architectures and has thus never been made before.

Our current method of choice to build complex systems is SOSIP (self-organizing surface-initiated polymerization.  The approach applies lessons from nature to address unresolved challenges with polymer chemistry.  Essential for success are molecular recognition within functional π-stacks and surrounding hydrogen-bonded networks as well as surface-initiated ring-opening disulfide-exchange polymerization.  Original initiators, propagators and strategies to create gradients and channels are highlighted on the JACS cover shown above. 

For synthetic access to multicomponent architectures, we are now expanding the SOSIP methodology to include templated self-sorting (TSS) and templated stack exchange (TSE).  Current projects focus on methods development to create multicomponent architectures with multiple channels and multiple gradients (SOSIP-TSE, SOSIP-TSE-TSS).  Triple-channel photosystems composed of naphthalenediimides, squaraines and fullerenes are among the most sophisticated surface architectures realized to date.

Other series of ongoing projects focus on the application of SOSIP to new chromophores (oligothiophenes, fullerenes, perylenediimides, phthalocyanines, porphyrins, squaraines), to new orthogonal dynamic covalent chemistry beyond disulfide and hydrazone exchange, and to charge-directing counterions or macrodipoles.

Methods:  This project is ideal for students who really like multistep organic synthesis (retrosynthetic analysis, modern synthetic methods (organometallics, µW, etc), purification techniques (TLC, flash, HPLC, RP-HPLC, SEC, etc), compound characterization (NMR, ESI, MALDI, HRMS, UV, IR, CD, mp, optical rotation, etc)).  SOSIP-TSE provides expertise in surface-initiated polymerization and dynamic covalent chemistry.  Photosystem characterization involves photocurrent generation (action spectra, current-voltage analysis, charge recombination efficiencies), cyclic voltammetry, absorption, fluorescence and circular dichroism spectroscopy, AFM, microcontact printing, etc.

Collaborations:  Ultrafast photophysics (Vauthey group), surface analytics (Borkovec group), computational simulation (Mareda).

Some recent references:  J. Am. Chem. Soc. 2013, 135, 12082; Chem. Sci. 2013, 4, 1847; Nature Chem. 2012, 4, 746; Chem. Sci. 2012, 3, 1492; J. Am. Chem. Soc. 2011, 133, 18542; J. Am. Chem. Soc. 2011, 133, 15228; J. Am. Chem. Soc. 2011, 133, 15224.