Acetylene spacer

For the central violene rc-system, we chose benzene with acetylene spacers for decreasing steric hindrance between the large cationic centers. Therefore, the tetracation 254 salt was designed as a first example for a hybrid with a cyanine unit at the both termini (27). As illustrated in Figure 22, tetracation 254 exemplifies a new hybrid system, which produces another cyanine substructure 252 by two-electron transfer. In this case, overall, four electron transfer should afford a fully neutralized species such as a neutral diradical. 

The bulky end groups and thin acetylenic spacer in hosts such as 7.13 are an example of the wheel and axel concept in inclusion compound design. The dictates of crystal close packing suggest that... 

In the chromophore-quencher system (1) a ferrocenyl unit is connected to a Ru(tpy)2 + unit via a p-phenylene-acetylene spacer [141]. The weak emission of the Ru(tpy)2 chromophore is completely quenched in the dyad [142]. For this system, an EnT mechanism could be inferred by analogy with the behavior of related bimolecular systems [140], but PET followed by fast back electron transfer cannot be ruled out. This mechanistic ambiguity is common to most studies on related chro-mophore-ferrocene dyads [143-146]. 

The DGTD belongs to a group of wheel and axle host molecules. Compared to the classical representative of this group (linear acetylenic spacer coupled with bulky end groups), DGTD can be called a four wheeled system where guest molecules can be included in the space between the front wheels (and/or rear wheels). 

Ducharme and Wuest have demonstrated that an unsymmetrical bis(2-pyridone) self-assembles as a homodimer in the solid state (Fig. 3).10 The 2-pyridone units were separated by an acetylenic spacer that allowed the molecule to adopt a syn conformation, wherein the two pyridone groups are oriented along the same side of the molecule. The molecule self-assembled via four N H -O hydrogen bonds. A symmetrical analog was also shown to form a hydrogen-bonded polymer. 

To relieve some of the angle strain at the saturated vertices of the smallest pericyclynes, we decided to explore the big brother compounds with 1,3-diyne units along each side in place of the shorter alkyne linkages. In the same sense that [A pericyclynes can be thought of as exploded cycloalkanes with acetylene spacers inserted between the corners [9], the new family with 1,3-diyne spacers can be thought of as exploded pericyclynes. 

A wide range of analogous polymers (e.g., 136) with acetylenic spacers has been prepared via the Pd-catalyzed polycondensation reactions between diiodoferrocenes and diethynyl arenes and has been very well characterized. 2,322a,322b polymer 136 (R = H) was found to be only partly soluble in organic solvents, the... 

Efficient energy transfers of >99, 98, and 88% are respectively observed for 93, 94, and 95. The phenyl acetylene spacer between the imidazole and the free base porphyrin of the acceptor in 94 seems to be the ideal compromise for efficient energy transfer and a high binding constant. This motif has thus been employed in a triad (96) in which a BODIPY has been added to the ZnP donor... 

The project by Sun et al. has been extended to photochemical production of H2 by a Ru(II) photosensitizer covalently linked to a proton reduction catalyst of dinuclear Fe carbonyl complex [128,129] (Fig. 25, left). The researchers synthesized (but did not isolate) a Ru(II) terpy complex connected to an [Fe2( x - SCH2N(Ph)CH2S)(CO)6] complex by an acetylene spacer [129] (Fig. 25, right). However, the photoproduction of H2 has not yet been reported. 

That this might be of use in liquid crystals was demonstrated many years later so that, for example, Marder, Viney, and coworkers prepared a number of rigid-rod materials with arene rings linked by acetylene spacers. When brought together in two-component systems where... 

Systems in which acetylenic spacers are placed between the pyridine and the thiophene rings have been reported (LVI). In these cases, the thiophene ring contained 3-hexyl or 3,4-dinitro groups [54]. These polymers can be electrochemical y n-doped more easily than they can be p-doped. These materials are also of interest because of their large third-order nonlinear optical properties. 

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