An efficient method for the synthesis of copillar[5]arenes was developed with FeCl₃ as catalyst and different 1,4-dialkoxybenzenes and paraformaldehyde as reactants (yields: 50–85%). The host–guest property of (co)pillar[5]arenes and terminal dibromoalkanes was investigated by ¹H NMR measurements and an X-ray study. The complexation behavior of the copillar[5]arenes can be tuned by changing the substituents on the host. A complete complexation selectivity was found between pillar[5]- and pillar[6]arenes, which is an interesting aspect for sensor techniques.

Advantages of the double branched dyes: better fixing, higher loading density, lower aggregation tendency, longer S ₁ lifetime on the TiO ₂ surface

The dimerization of anthracene by a [4π + 4π] cycloaddition is one of the oldest and best known reactions in photochemistry. In the series of tethered bichromophoric arenes, this reaction type could be extended to anthracene–naphthalene, naphthalene–naphthalene and recently even to anthracene–benzene and naphthalene–benzene systems. Cyclophanes, which can be regarded as twofold or multiple tethered systems, are not discussed here. The cycloisomerizations are performed by irradiation at the long-wavelength absorption (λ > 270 nm), whereas shorter wavelengths (λ < 270 nm) lead to cycloreversions, which can be also achieved by a thermal route. The systems represent therefore a P- and T-type photochromism, which can be used for optical or chiroptical switches. An acceleration of the switch is possible by a singlet energy transfer (light harvesting antenna effect) in dendritic compounds. In the past 5 to 10 years many applications of these switches were studied in the context of photonic devices, sensor techniques, lithographic processes, imaging techniques, data processing and data storage.

In this paper, the encapsulated insulated molecular wire (EIMW) and 2′,7′-bis(hexyloxy)spiro[cyclopenta[2,1-b:3,4-b′]dithiophene-4,9′-fluorene] (SPDF) were specifically designed as efficient anti-aggregation π-bridges for two novel D–A–π–A metal-free sensitizers (IBT1 and IBT2). Compared with the reference dye IBT3 with 3,3′-dihexyl-2,2′-bithiophene (DHBT) as an anti-aggregation π-bridge, both the dyes IBT1 with EIMW and IBT2 with SPDF as π-bridges can suppress intermolecular aggregation more efficiently. The π-bridge of SPDF shows the strongest anti-aggregation ability due to the rigid ‘T’ configuration among these dyes. Meanwhile, the π-bridge of EIMW shows better anti-aggregation ability than DHBT because of the larger steric hindrance of the former. Finally, when the dyes IBT1 and IBT2 are co-sensitized with IBT3, respectively, the new devices exhibit high efficiencies of 7.85% and 7.64%, respectively, which are comparable to that of N719 (7.85%). The results demonstrate that the dyes with EIMW and SPDF as anti-aggregation π-bridges are promising candidates for efficient DSSCs and dye aggregation can be effectively inhibited by structural engineering of the π-spacer.