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.