Near-infrared Absorbing Polymethine Dyes Terminally Substituted by 1-Benzothiopyrylium Ring

Abstract Unsymmetrical polymethine near-infrared dyes terminally containing 1-benzothiopyrylium ring and N,N-dimethylamino group were first prepared from 2-methyl-, 4-methyl-, and 2,4-dimethyl-1-benzothiopyrylium salts. It is found that the maximum wavelength of these dyes on PMMA is remarkably shifted to a shorter wavelength (60–200 nm) compared with that in solution.