Synthesis, optical properties and crystal structure of (E,E)-1,3-(3,4:9,10-dibenzododeca-1,11-diene-5,7-diyne-1,12-di-yl)benzene.

The de-hydro-benzannulene (E,E)-1,3-(3,4:9,10-dibenzododeca-1,11-diene-5,7-diyne-1,12-di-yl)benzene, C(26)H(16), was successfully synthesized via photocatalyst-assisted stereoselective reductive de-sulfonyl-ation of 1,3-bis-{1-phenyl-sulfonyl-2-[2-(tri-methyl-silylethyn-yl)phen-yl]ethen-yl}benzene, C(44)H(42)O(4)S(2)Si(2), and subsequent desilylative cyclization of the resulting (E,E)-bis-silyl-protected dienyne, C(32)H(34)Si(2). The structure of the de-hydro-benzannulene thus obtained was confirmed by single-crystal X-ray analysis; three benzene rings are connected to one another by a 1,3-butadiynylene and a pair of ethenylene arrays. Although the π-system expanded efficiently in the de-hydro-benzannulene, it was observed that the butadiynylene and ethenylene arrays were strained, showing smaller [171.3†(2)-172.6†(2) °] and larger bond angles [122.5†(2)-131.9†(2)°] than the conventional bond angles, respectively. In CHCl(3), the de-hydro-benzannulene showed the longest absorption band at 377†nm. When irradiated by UV light, it emitted fluorescence at 468†nm (Φ(F) = 0.26) and 504†nm (Φ(F) = 0.24) in CHCl(3) and in the powdered state, respectively.