Layer-by-layer assembly of two palladium coordination-based multilayers on silicon and glass substrates is presented. The new assemblies consist of rigid-rod chromophores connected by terminal pyridine moieties to palladium centers. Both colloidal palladium and PdCl2(PhCN)2 were used in order to determine the effect of the metal complex precursor on multilayer structure and optical properties. The multilayers were formed by an iterative wet-chemical deposition process at room temperature in air on a siloxane-based template layer. Twelve consecutive deposition steps have been demonstrated resulting in structurally regular assemblies with an equal amount of chromophore and palladium added in each molecular bilayer. The optical intensity characteristics of the metal-organic films are clearly a function of the palladium precursor employed. The colloid-based system has a UV-vis absorption maximum an order of magnitude stronger than that of the PdCl2-based multilayer. The absorption maximum of the PdCl2-based film exhibits a significant red shift of 23 nm with the addition of 12 layers. Remarkably, the structure and physiochemical properties of the submicron scale PdCl2-based structures are determined by the configuration of the approximately 15 angstroms thick template layer. The refractive index of the PdCl2-based film was determined by spectroscopic ellipsometry. Well-defined three-dimensional structures, with a dimension of 5 microm, were obtained using photopatterned template monolayers. The properties and microstructure of the films were studied by UV-vis spectroscopy, spectroscopic ellipsometry, atomic force microscopy (AFM), X-ray reflectivity (XRR), scanning electron microscopy (SEM), and aqueous contact angle measurements (CA).

A new partially fluorinated stilbazole represents the first example of a halogen bonding based donor-acceptor system which exhibits an intriguing solid-state structure consisting of infinite parallel helices.The use of halogen bonding (XB) interactions in co-crystallization and solid-state reactivity is of much current interest as well as exploratory studies in areas as different as materials science and biology. 1 Despite several theoretical/experimental investigations supporting XB as a chemical tool, 1a the design/realization of molecular structures for XB driven formation of supramolecular assemblies is considerably limited compared to that based on hydrogen bonding (HB). 1e The majority of XB-based networks consist of a separate halogen bond donor (D) and an acceptor (A) molecules (e.g., … D-D … A-A … D-D … A-A … ). Examples of bifunctional compounds including both halogen bond D and A sites are relatively rare. 2 For instance, recently we reported the synthesis, solution optical (UV/vis) properties, and crystal structure of a partially fluorinated stilbazole (1) combining both D-A sites for XB. 3 This D-A arrangement and p-p stacking combined with the rod-like structure of the stilbazole (1) indeed led to a linear chain type motif in the crystal structure. It is known that variation of the positions of D and/or A sites results in the formation of zigzag type patterns. 4 When multiple D and/or A sites are available, the resulted network may exhibit ''secondary'' structures such as helices. HB and metal coordination have been widely exploited to self-assemble helical architectures. 5 In contrast, examples of XB as a directing tool for the construction of helical suprastructures are rare. 4a,6 Moreover, the use of bifunctional molecules combining both the D and A sites for XB to obtain unimolecular helical systems is unknown.We introduce here a multiple D-A system (2) that provides a new entry in the design and formation of unimolecular halogen bonded networks that can form sophisticated 3-D motifs with a high degree of complexity. This new fluorinated stilbazole derivative (2) combines one hydrocarbon (HC) XB acceptor with two perfluorocarbon (PFC) multifunctional XB donor/acceptor sites in one conjugated molecule. In addition, the solid-state

Trimethoxy-[11-(2-nitrobenzyloxy)undecyl]silane (1) and trimethoxy-[17-(2-nitrobenzyloxy)heptadecyl]silane (2) have been used for the covalent assembly of siloxane-based photopatternable monolayers. Exposing the monolayers to UV light (312 +/- 10 nm) results in the generation of reactive hydroxyl-terminated monolayers without affecting the film quality. The new monolayers, deprotection chemistry, and the effect of photoinduced headgroup lift-off on the monolayer microstructure have been studied in detail by a full complement of physicochemical techniques, including optical (UV-vis) spectroscopy, ellipsometry, aqueous contact angle (CA) measurements, X-ray photoelectron spectroscopy (XPS), synchrotron X-ray reflectivity (XRR), and atomic force microscopy (AFM and AFM-force spectroscopy). AFM-force spectroscopy was used to analyze hydrogen-bond interactions as a function of the nature of the solid-liquid interface. AFM-force spectroscopy indicates a hydrogen-bond energy for photodeprotected monolayers of 8.2 kJ mol(-1) (approximately 2 kcal mol(-1)). Scanning electron microscopy (SEM) revealed that treatment of photopatterned monolayers with ZnEt2 solutions resulted in well-defined approximately 2 microm x 2 microm features of 10 A thick ZnO layers.