Controlling the dimensionality of on-surface coordination polymers via endo- or exoligation.

The formation of on-surface coordination polymers is controlled by the interplay of chemical reactivity and structure of the building blocks, as well as by the orientating role of the substrate registry. Beyond the predetermined patterns of structural assembly, the chemical reactivity of the reactants involved may provide alternative pathways in their aggregation. Organic molecules, which are transformed in a surface reaction, may be subsequently trapped via coordination of homo- or heterometal adatoms, which may also play a role in the molecular transformation. The amino-functionalized perylene derivative, 4,9-diaminoperylene quinone-3,10-diimine (DPDI), undergoes specific levels of dehydrogenation (-1 H2 or -3 H2) depending on the nature of the present adatoms (Fe, Co, Ni or Cu). In this way, the molecule is converted to an endo- or an exoligand, possessing a concave or convex arrangement of ligating atoms, which is decisive for the formation of either 1D or 2D coordination polymers.

Covalent assembly of a two-dimensional molecular "sponge" on a Cu(111) surface: confined electronic surface states in open and closed pores.

We present a new class of on-surface covalent reactions, formed between diborylene-3,4,9,10-tetraaminoperylene and trimesic acid on Cu(111), which gives rise to a porous 2D-'sponge'. This aperiodic network allowed the investigation of the dependence of electron confinement effects upon pore size, shape and even in partial confinement.

Tuning redox chemistry and photophysics in core-substituted tetraazaperopyrenes (TAPPs).

Core substitution of tetraazaperopyrenes (TAPPs) has been achieved, and with it, considerable variation of their photo- and redox-chemical properties. Through Suzuki cross coupling starting from the fourfold core-brominated tetraazaperopyrene, aryl-substituted TAPPs were synthesized, which displayed very high fluorescence quantum yields (up to 100 %) in solution. Besides the Suzuki reactions, Stille and Sonogashira cross-couplings were also found to be suitable methods for core derivatization, as demonstrated in the syntheses of alkynyl-substituted tetraazaperopyrene congeners. Furthermore, TAPPs incorporating intramolecular donor-acceptor combinations of aromatic units (8, 9) were accessible by coupling the electron-poor peropyrene core with electron-rich aromatic units, which act as strong electron donors. Finally, C-heteroatom coupling (O, S, N) gave rise to novel TAPP derivatives with strongly modified redox-chemical behaviour and photophysics in the solid state as well in solution. In particular, TAPP derivatives displaying red fluorescence were obtained for the first time.

1,3,6,8-Tetraazapyrenes: synthesis, solid-state structures, and properties as redox-active materials.

A series of new tetraazapyrene (TAPy) derivatives has been synthesized by reducing 1,4,5,8-tetranitronaphthalene to its corresponding tin salt (I) and reacting it with perfluorinated alkyl or aryl anhydrides. The resulting 2,7-disubstituted TAPy molecules and the known parent compound 1,3,6,8-tetraazapyrene (II) have been further derivatized by core chlorination and bromination. The brominated compounds served as starting materials for Suzuki cross-coupling reactions with electron-poor arylboronic acids. Single-crystal X-ray analyses established polymorphism for some TAPy compounds. The ground-state geometries of all new TAPy derivatives were modeled with DFT methods [B3PW91/6-31 g(d,p) and B3PW91/6-311+g(d,p)], especially focusing on the energies of the lowest unoccupied molecular orbital (LUMO) and the electron affinities (EA) of the molecules. The results of the calculations were confirmed experimentally by cyclic voltammetry to evaluate the substitution effects at the 2 and 7 position and the core positions, respectively, and gave LUMO energy levels that range from -3.57 to -4.14 eV. Fabrication of organic field-effect transistors (OFETs) with several of these tetraazapyrenes established their potential as organic n-type semiconductors.

Tetrachlorinated tetraazaperopyrenes (TAPPs): highly fluorescent dyes and semiconductors for air-stable organic n-channel transistors and complementary circuits.

A range of 2,9-perfluoroalkyl-substituted tetraazaperopyrene (TAPP) derivatives (1-5) was synthesised by reacting 4,9-diamino-3,10-perylenequinone diimine (DPDI) with the corresponding carboxylic acid chloride or anhydride in the presence of a base. The reaction of compounds 1-4 with dichloroisocyanuric acid (DIC) in concentrated sulphuric acid resulted in the fourfold substitution of the tetraazaperopyrene core, yielding the 2,9-bisperfluoroalkyl-4,7,11,14-tetrachloro-1,3,8,10-tetraazaperopyrenes 6-9, respectively. The optical and electrochemical data demonstrate the drastic influence of the core substitution on the properties. All compounds are highly luminescent (fluorescence quantum yields of up to Φ=0.8). The LUMO energies of the tetrachlorinated TAPP derivatives (determined by cyclic voltammetry and computed by DFT calulations) were found to be below -4 eV. In the course of this work the performance of TAPP derivatives in organic thin-film transistors (TFTs) was investigated, and their n-channel characteristics with field-effect mobilities of up to 0.14 cm(2) V(-1) s(-1) and an on/off current ratio of >10(6) were confirmed. Long-term stabilities of 3-4 months under ambient conditions of the devices were established. Complementary inverters and ring oscillators with n-channel TFTs based on compound 8 and p-channel TFTs based on dinaphtho-[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) were fabricated on a glass substrate.

Substitutent effects in the periphery of 2,9-bisaryl-tetraazaperopyrene dyes.

A series of 2,9-bisaryl-1,3,8,10-tetraazaperopyrene (TAPP) derivatives has been synthesized by reacting 4,9-diamino-3,10-perylenequinone diimine with a large excess of the corresponding benzoyl chloride in refluxing nitrobenzene. Among all derivatives only ortho-substituted phenyl congeners were sufficiently soluble for studying solutions of defined concentration in organic solvents. The molecular structures of the crystallized compounds, determined by X-ray diffraction of four derivatives, are determined by the planar tetraazaperopyrene core and the interplanar angle of the phenyl rings, which depends on the size of the ortho substituent (40-70°). The intermolecular packing pattern of all compounds is characterized by parallel stacks of molecules with the substituted phenyl rings rotated out of the peropyrene plane to reduce the steric repulsion. Crystals of a TAPP derivative suitable for X-ray diffraction were grown from trifluoroacetic acid (TFA) for the first time, establishing a 2-fold protonated species. The ground-state geometries of the TAPP derivatives were calculated by DFT [B3PW91/6-31g(d,p)] and the lowest unoccupied molecular orbital (LUMO) energies of derivatives possessing electron-withdrawing groups were decreased, as were the computed electron affinities. The results of the modeling study were confirmed experimentally by cyclic voltammetry to evaluate the substituent effects on the highest occupied molecular orbital (HOMO) and the LUMO of the peropyrene core. The UV-vis absorption spectra of all compounds recorded in trifluoroacetic acid are almost superimposable and display a characteristic visible absorption band between 460 and 490 nm (log ε = 4.64-5.01) with a strong vibrational progression of 1173-1475 cm(-1). Their fluorescence spectra are characterized by bands between 490 and 530 nm that are the mirror images of the absorption spectra (Stokes shifts of 10-50 nm). The luminescence quantum yields range from <0.01 to 0.30, thereby indicating a quenching effect for some substitution patterns.