Azobenzenophanes, in which two (2), three (3), and four (4) azobenzene units are connected cyclically by methylene linkers at the meta positions, were synthesized. The effect of ring strain on the structure and the photochemical and the thermal isomerization of azobenzene were investigated. Complex formation with guest species such as alkali metal cations and solvent molecules was observed. X-ray crystal analyses revealed the crystal structure of all three isomers of 2. Compound 2(t,c) was distorted due to the ring strain and 2(c,c) was not deformed. Both 3 and 4 formed supramolecular channel structures in which an azobenzenophane molecule holds a solvent molecule in the molecular cavity. Upon exposure to light, 2, 3, and 4 exhibited stepwise trans-cis photoisomerization in solutions. The quantum yields for all isomerization steps of 2 were determined, and these values suggested that interactions between chromophores such as energy transfer and/or steric distortion affect the isomerization process. The lifetime of 2(c,c) (19.7 days) was longer than that of 2(t,c) (6.1 days) at room temperature. The relative stability of these isomers was explained by the isokinetic (or compensation) relationship between deltaH++ and deltaS++ values and by the effect of the ring strain. The relative energies of three isomers of 2 were estimated by HF/6-31G** calculations, and these values indicated that 2(t,c) has the largest ring strain. Complexes (1:1 and 2:1) between macrocycles and alkali metal cations (Li+, Na+, K+, Rb+, Cs+) were observed by ESIMS. The cation selectivity was shifted upon photoirradiation especially in 4.

[formula: see text] [1.1](3,3')-Azobenzenophane, in which two azobenzenes are cyclically connected by -CH2- chains at the meta positions, has been synthesized. The crystal structures of all isomers have been revealed. This is the first report on the crystal structure of the cis isomer of macrocyclic azobenzenes. The trans,trans isomer was slightly distorted, the trans,cis isomer highly deformed, and the cis,cis isomer unstrained. The thermal stability of cis isomers in solutions are deducible from the crystal structures.