3,6-Bis(dimethylamino)fluorenylium dye ethynologues: new highly coloured π-electron systems

Abstract
Acetylenic analogues (3) of 3,6-bis(dimethylamino)fluorenylium dyes, which absorb near-IR light (up to 1056 nm in CH2Cl2), have been prepared; their characteristic absorption properties are discussed on the basis of PPP–Cl–MO calculations.