Triphenylmethane dye ethynologues with absorption bands in the near infrared

Abstract

The first examples of triphenylmethane dye ethynologues (9)[4-(dimethylamino)phenylethynylxanthenylium,-thioxanthenylium, and -selenoxanthenylium perchlorates] absorbing in the near i.r. (up to 802 nm in CH₂Cl₂) have been synthesized by treatment of the corresponding alcohols (8) with acids, and their absorption spectral properties and chemical structures have been investigated and compared with the results of Pariser–Parr–Pople MO calculations. It has been shown that contribution of positive-charge-delocalized structures [resonance hybrids (9), (9′), and (9″)] is effective and independent of the counter ions.