Hierarchical Interactions by Light-Induced Generation of Heterogeneous Templates – HI-LIGHT

The in-situ modification of monolayers grafted onto metal or semiconductor surfaces with sub-micron resolution represents a formidable challenge that is central for the development of surface-bound molecular nanotechnology. Thanks to huge efforts by several world-leading research laboratories, the first molecular "print boards" in which chemical recognition can be spatially addressed have recently emerged. We believe it is now possible to construct the next generation of such devices, capable of read – write – erase functionality. Furthermore, through control of molecular recognition events, the assembly of advanced, precisely defined architectures can be directed by molecular interactions that are hierarchically ordered. The system we propose is based on a photoactive receptor for barbiturate derivatives recently developed by Partner 1, in which the photoinduced dimerization of pendant anthracenes covalently locks the receptor in a "closed" geometry. The deposition of these receptors on a variety of conducting, semi-conducting or insulating surfaces will be readily achieved via the synthesis of a common intermediate. The dynamic range in binding affinity of the open vs. closed form (1000-fold) is unprecedented and, combined with the high selectivity of the multi-point hydrogen binding motif of the receptor, opens new perspectives for the reversible control of molecular recognition. Once the receptor is immobilized on a surface, it will be possible to use 365 nm light (uniform or through a mask) to induce intramolecular photodimerization and conversion of the open receptor to the closed form. We will then be able to use scanning electrochemical microscopy (SECM), conductive-AFM, or STM to locally reduce (or oxidize) the anthracene dimer in the closed receptors and trigger its conversion to the open form. This form of electrochemical "writing" will allow us to pattern the surface with much greater precision and freedom than would be possible using a mask. At any moment, irradiation with long-wavelength light can be used to convert the open receptors back to the closed form, thus providing a mechanism for "erasing" the molecular information previously stored This interdisciplinary project brings together photochemists, electrochemists, and solid-state physicists to not only prepare and demonstrate recognition-based read – write – erase molecular print boards, but also their use for the construction of organic field-effect transistors (OFET) and also in the design of experiments aimed at probing energy and electron transfer processes at the single molecule level using time-resolved confocal fluorescence microscopy. All of the instrumentation required for the project, including SECM, AFM, STM and the confocal microscopy setup, is available in the proposed consortium. Additionally, a wide variety of electro- and photo-active molecules, including fullerenes, Au and CdS nanoparticles, and oligothiophenes and oligophenylenevinylenes possessing a barbituric acid molecular recognition site are available from previous work. These compounds will bind the open receptors and allow us to fabricate and study new OFET-based devices for molecular electronics. The consortium will use available knowledge to jump-start the project by leveraging existing collaborations between three of the partners. Thanks to substantial participation by all the participants and the recruitment of one pre-doc and two post-doc positions, rapid progress will be made on the synthesis of the modified receptors and their deposition on silicon, gold, and silicon oxide surfaces (Partner 1). Using methodology currently available to Partner 2, patterning via scanning probe microscopy will be used to modify the immobilized receptors immobilized on substrates suitable for the construction of OFETs (Partner 3) or confocal microscopy experiments (Partner1).