Synthesis and absorption spectral shifts of novel squarylium dyes

Two kinds of new squarylium dyes have been prepared. Aminosquarylium dyes (ASQ) (6) have been prepared by condensation of aminosquarates (3) and 1-ethyl-2,3,3-trimethylindolenium iodide (5). New aminosquarylium dye 6a absorbed at a longer wavelength (18 nm) than the corresponding squarylium dye (SQ) 7c. A new class of dithiosquarylium dyes (DTSQ 8) has also been synthesized by the reaction of squarylium dye (SQ) with Lawesson's reagent or P4S10. The lambda(max) of DTSQ dues undergoes a bathochromic shift of about 25 nm compared with corresponding SQ dyes. The visible absorption spectra of ASQ and DTSQ dyes are well accounted for by PPP-MO calculations.