Achieving Ultra‐Narrow‐Band Deep‐Red Electroluminescence By a Soliton‐type Dye Squaraine

Due to the soliton‐like electronic structural characteristics, cyanine dyes typically exhibit spectral behaviors such as large molar extinction coefficients, narrow spectra, and high fluorescence efficiency. However, their extensive applications as emitters in electroluminescence are largely ignored due to their serious emission quenching in the aggregation state. Herein, it is reported a squaraine dye (a type of cyanine) SQPhEt. At different solution concentrations, the unusual decrease in full‐width at half‐maxima (FWHM) with increasing Stokes shift indicates the fluorescence quenching of SQPhEt in the aggregated state is because of the strong self‐absorption effect. A sensitized device structure can help to reduce the doping concentration of dye, which can effectively suppress self‐absorption. Benefitting from the large molar extinction coefficient of SQPhEt, even at low doping concentrations of 0.1 wt%, efficient Förster energy transfer can be achieved. The corresponding spin‐coating sensitized device based on SQPhEt as the dopant exhibits favorable deep‐red emission at 668 nm with a small FWHM of 0.10 eV. Squaraine dyes typically exhibit narrow emission spectra due to their soliton‐like electronic structure characteristics. An organic light‐emitting diode based on soliton‐type squaraine dye is prepared, overcoming the luminescence quenching induced by dye aggregation. The deep‐red electroluminescence peak is located at 668 nm, with a full‐width at half‐maximum (FWHM) of only 0.10 eV.