Synthesis and properties of 3,6-bis(dimethylamino)fluorenylium dye ethynologues: new highly bathochromic π-electron system

A series of acetylenic analogues of 3,6-bis(dimethylamino)fluorenylium dye, which absorb near-IR light (up to 1096 nm in CH2Cl2), have been systematically prepared and their characteristic lightabsorption spectroscopic properties, as well as their pKR+-values, are discussed with the aid of PPP-SCF-MO calculations, and compared with data for the corresponding unbridged triphenylmethane dye ethynologues.