Glass-forming non-symmetric bis-styryl-DWK-type dyes for infra-red radiation amplification systems

A series of D-π-A type organic dyes with bulky triphenylmethyl moiety containing 2,6-bis-(4-substituted)styryl-4H-pyran-4-ylidene donor (D) fragments and different electron acceptors (A) were synthesized and investigated, mostly for potential applications in organic solid-state lasers as infra-red (IR) radiation amplification medium. Dye glass transition temperature is above 99 °C with thermal stability in the region from 173 °C to 326 °C which was slightly influenced by the electron acceptor fragment attached to the 4H-pyrane ring in 4-position. Introducing substituents in 4-position within one of the styryl-fragments with stronger electron withdrawing properties decreased ASE excitation threshold values (E_th) up to 180 μJ/cm² in dye spin-cast neat films and shifted photoluminescence and amplified spontaneous emission (ASE) processes into the infra-red (IR) region. Although more studies are required, some of the investigated non-symmetric bis-styryl-DWK-dyes show potential as a solution-processable gain medium for IR radiation amplification.