Development of thermally-stable NIR absorbing films based on heptamethine cyanine dyes with bistriflimide anion

Development of benzo[cd]indolenyl cyanine dyes for NIR-absorbing films and elucidation of molecular structure–spectroscopic relationship

“…Because the cyanine dyes were well dissolved in the dichloromethane solvent, the substitution of anions did not affect the λ max of the dyes. 11 Cy-5(B) showed a bathochromic shift of 26 nm and higher ε than the other dyes. In addition, a slight hypsochromic shift of 4 nm was observed in Cy-p6 compared with Cy-6 and Cy- t 6 .…”

“…The HOMO and LUMO orbitals are delocalized throughout the polymethine chain and the benzo[ cd ]indole ring, which is clearly different from the indolium- and benzo[ e ]indolium-based cyanines reported in previous studies, in which the heteroaryl makes only a small contribution to the frontier molecular orbitals. 11,13,32 The heavy participation of the benzo[ cd ]indole ring in the FMOs resulted in a strong bathochromic shift, making the λ max value to be above 1000 nm.…”

“…65–67 Because NIR absorption originates from the delocalized π-conjugation of the polymethine chain, deterioration in NIR absorbance may occur even before any observable thermal weight loss. 11…”

“…Heptamethine cyanine dyes are highly promising candidates for optical filter applications because of their excellent visible light transmittance and strong NIR absorption. 10–12 Among them, benzo[ cd ]indolenyl substituted heptamethine cyanine dyes exhibit a maximum absorption wavelength ( λ max ) greater than 1000 nm, making them suitable for NIR filter applications that require long-wavelength absorption. 13 However, despite their remarkable optical properties, they encounter limitations when applied to films due to inherent drawbacks resulting from their structural properties.…”