Near‐Infrared Emission by Tuned Aggregation of a Porphyrin Compound in a Host–Guest Light‐Emitting Electrochemical Cell

Abstract The synthesis of 5,10,15,20‐tetrakis((5,10‐bis((2‐hexyldecyl)oxy)dithieno[3,2‐c:3′,2′‐h][1,5]naphthyridin‐2‐yl)ethynyl)porphyrin zinc(II) (Por4NT), a near‐infrared (NIR) emitting compound, comprising a zinc porphyrin core linked with triple bonds through its meso positions to four 5,10‐bis((2‐hexyldecyl)oxy)dithieno[3,2‐c:3′,2′‐h][1,5]naphthyridine (NT) arms is reported. Por4NT featured high solubility in common non‐polar solvents, which is ideal for easy processing through solution techniques, and high photoluminescence (PL) efficiency of ≈30% in dilute toluene solution. It also exhibited a strong tendency for aggregation because of its flat conformation, and this aggregation resulted in a strong redshifted emission and a drop in PL efficiency. A well‐matched PBDTSi‐BDD‐Py “host” terpolymer is therefore designed, which is capable of mitigating the aggregation of the Por4NT “guest”. An optimized blend of the host, guest, and an ionic‐liquid electrolyte is utilized as the active material in a light‐emitting electrochemical cell (LEC), which delivered strong NIR radiance of 134 µW cm^‐2 with a long wavelength maximum at 810 nm at a low drive voltage of 5.0 V. The attainment of the strong NIR emission from the host–guest LEC is attributed to a tuned aggregation of the Por4NT emitter, which resulted in the desired aggregation‐induced redshift of the emission at a reasonably retained efficiency.