A family of planar oligothiophene/imidazole/1,10-phenanthroline (OTIP)-based heterocyclic, aromatic, semiconducting, and fluorescent compounds with N-substituted alkyl chains (allyl, n-butyl, n-octyl, n-dodecyl, and n-cetyl) have been designed and synthesized. They all have specific N-coordination sites, various donor–acceptor spacers, good molecular planarity, suitable solubility, and high thermal stability. In comparison with conventional double β-alkylation of the thiophene ring, our results reveal that the single imidazole N-alkylation strategy for OTIPs has the advantage of maintaining the planarity of the whole molecule, in addition to improving the solubility, which can be clearly verified by the small dihedral angles between adjacent thiophene/imidazole/1,10-phenanthroline (TIP) rings in eight X-ray single-crystal structures. In particular, n-dodecyl- and n-cetyl-substituted OTIPs (7 and 8) with the same molecular length of 2.37 nm (M_W=939 and 1052), show good molecular planarity with the aforementioned dihedral angles of 8.9(5) and 10.4(5)°. Furthermore, special attention has been paid to the physicochemical properties of seven symmetrical OTIPs (6–8, 13–15, and 19), including two to six thiophene rings in the middle of their molecular structures. To the best of our knowledge, this is the first synthetic, structural, and spectral investigation into the N-alkylation of OTIP-based compounds.

A series of T- and H-shaped donor–acceptor (D–A) types of dipyrido[3,2-a:2′,3′-c]phenazine (DPPZ)-based molecules, extended by thienyl and triphenylamino chromophores at the 2,7-(bottom) and/or 10,13-positions (top), have been designed and prepared successfully. Synthetic, structural, thermal, spectral, and computational comparisons have been carried out for related compounds because of their adjustable intramolecular charge-transfer properties. It is noted that a pair of structural isomers (5 and 6) has been obtained, respectively, where distinguishable UV/Vis and fluorescence spectra, electrochemical activity, thermal stability, and bandgaps are observed. Furthermore, compounds 6, 8, 10, 11, 13, and 15 exhibit excellent thermal stability, and the Td₁₀ values for them are found to range from 524 to 646 °C, which can be regarded as one of the best groups of thermally stable compounds among organic small molecules. In addition, theoretical calculations were performed, and the structure–property relationships were examined to reveal the effects of the position and number of donor arms on the DPPZ acceptor core.

Two new flexible extended dialdehydes (H₂hpdd and H₂pdd) with different functional pendant arms (CH₂CH₂PhOH and CH₂CH₂Ph) have been synthesized and reacted with 1,2-bis(2-aminoethoxy)ethane to prepare Schiff-base macrocyclic complexes in the presence of a Zn^II-ion template. As a result, two preorganized dinuclear Zn^II intermediates (1 and 2), as well as two 42-membered folded [2+2] macrocyclic dinuclear Zn^II complexes (3 and 4), were produced. The central zinc ions in compounds 1–4 showed distinguishable coordination patterns with the dialdehydes and the [2+2] macrocyclic ligands, in which a subtle pH-adjustment function of the two pendant arms (with or without the phenolic hydroxy group) was believed to play a vital role. Furthermore, cation- and anion-recognition experiments for complexes 3 and 4 revealed that they could selectively recognize acetate ions by the formation of 1:1 stoichiometric complexes, as verified by changes in their UV/Vis and MS (ESI) spectra and even by the naked eye.

A new 1,10-phenanthroline (Phen) derivative, 3,8-bis(5-methylthiophen-2-yl)-1,10-phenanthroline (PHT1), has been synthesized and fully characterized including by single-crystal X-ray structure analysis. The electron-donating effects of the two 5-methylthiophene groups lead to distinctive fluorescence emission enhancement on complexation with Zn²⁺ compared with non-emissive Phen. However, PHT1 shows stronger Zn²⁺-sensing ability than 3,8-bis(thiophen-2-yl)-1,10-phenanthroline (PHT0) or 3,8-bis(3-methylthiophen-2-yl)-1,10-phenanthroline (PHT2) and longer-wavelength fluorescence emission (λ_em = 461 nm), which is vital for studies of living systems, mainly because of the lower steric hindrance and the electron-donating effects of the 5-methyl groups on the thiophene rings. More interestingly, PHT1 displays high selectivity towards Zn²⁺ over a broad range of pH and has an extremely low detection limit (5 ppb). An approximately 51-fold Zn²⁺-selective CHEF response has been attributed to the formation of a 1:2 metal–ligand complex, and the association equilibrium constant (K_ass⁰) of [Zn(PHT1)₂](ClO₄)₂ was determined to be 3.4 × 10¹². Anionic effects and variations in the ¹H NMR spectra before and after zinc(II) ion complextion were observed. Moreover, the ability of probe PHT1 to sense Zn²⁺ within living HL-60, yeast, and HepG-2 cells has been explored, and the Zn²⁺-probing process in living cells was found to be reversible with a zinc chelator solution of N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN).

The synthesis and spectral and structural characterization of a new family of ruthenium(II) complexes containing 3-bromo-, 3,8-dibromo-, 3-(thiophen-2′,2″-yl)-, and 3,8-(thiophen-2′,2″-yl)-1,10-phenanthroline (phen) ligands is described. UV/Vis spectroscopy is used to compare the differences between the conjugated π systems in these ligands and their respective [Ru(bpy)₂]²⁺ (bpy = 2,2′-bipyridine) analogs. Density functional theory (DFT) computations have been carried out to compare the energy differences between the single-crystal and the energy-minimized structures for different conformations (trans/trans, trans/cis and cis/cis) of the thiophene rings and their bonded phen ring. The formation of an oligothiophene semiconductor polymer bridging gold electrodes with a gap of around 25 nm gap from Ru^II complex 7 by in situ electropolymerization, and its removal, is monitored by scanning electron microscopy (SEM). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)