Solution‐Processable Tris(5‐substituted 8‐hydroxyquinolinato)aluminum Complexes as Active Matrix for Organic Solid‐State Laser Applications

A series of glassy 5‐substituted 8‐hydroxyquinolinato aluminum complexes with good film‐forming ability via wet‐casting methods were successfully synthesized in sufficient purity by using aluminum nitrate and investigated for applications in tris(8‐hydroxyquinolinato)aluminum (Alq 3 ): 4‐(dicyanomethylene)‐2‐methyl‐6‐(4‐dimethylaminostyryl)‐4 H ‐pyran (DCM)‐type organic solid‐state lasers systems. Synthesized glassy Alq 3 complexes form neat films from solutions and show glass transition temperatures up to 108°C with thermal stability above 156°C. The incorporation of bulky triphenyl and Boc groups through methoxy and methylpiperazine linkers in 5‐position of the 8‐hydroxyquinolinato ligands only slightly influenced absorption and emission characteristics of synthesized Alq 3 complexes in comparison to the unsubstituted Alq 3 . A twofold increase in photoluminescence quantum yield of synthesized complexes in the solid state (up to 18.8%) relative to solution (up to 9.3%) is observed. This behavior is attributed to aggregation‐induced emission arising from restricted intramolecular motions in the amorphous films, despite the presence of concentration‐dependent aggregation‐caused quenching at intermediate aggregation levels. A successful demonstration of Förster resonance energy transfer (FRET) from a bulky 2‐(4‐methylpiperazin‐1‐yl)ethyl‐3,3,3‐triphenylpropanoate‐substituted aluminum complex to a solution‐processable DCM derivative confirms the feasibility of fully solution‐processed Alq 3 :DCM‐type light‐emitting gain media, enabling wet‐casting deposition strategies for the design, investigation, and fabrication of organic solid‐state lasers.