From Donor–Donor Exciplex-Forming Interfaces to Detection of an Explosive Compound with Phenylethenyl Derivatives Redefining OLED Efficiency and Extremely High Sensitivity to Picric Acid

In this study, three derivatives of phenylethenyl-substituted phenoxazine and phenothiazine are synthesized via Buchwald-Hartwig cross-coupling, targeting multifunctionality as exciplex-forming materials and efficient cyan emitters for organic light-emitting diodes (OLEDs) and sensitive dectectors of picric acid. Advanced density functional theory (DFT) calculations at the mPW1PW91/6–31G(d,p) level unveil the intricate electronic architectures of these compounds, emphasizing their spatial molecular orbitals and the charge-transfer dynamics governing excited-state properties. Reorganization energy calculations indicate superior hole mobility, particularly for derivatives with tetraphenylethenyl groups. Photophysical investigations reveal aggregation-induced emission enhancement (AIEE) in water-THF mixtures, with cyan fluorescence intensifying at high water fractions (fw% = 99) due to the formation of emissive aggregates. Photoluminescence quantum yields (PLQYs) are significantly higher of solid films (13.5–53%) compared to those of dilute toluene solutions (3–26%). This observation is attributed to enhanced intermolecular interactions and aggregate formation. The emissive aggregates of the compounds exhibit extremely high sensitivity to electron-deficient picric acid via noncovalent interactions with Stern–Volmer constants up to 2.96 × 104 M–1. This is attributed to their strong donor–acceptor charge-transfer mechanisms. OLEDs employing these materials as emitters display bluish-cyan electroluminescence (λmax≈500 nm), with brightness surpassing 1000 cd/m2 and external quantum efficiencies (EQEs) ranging from 2.5 to 6%. The relatively high EQEs are explained by triplet harvesting from interface donor–donor exciplexes.