Systematic Control of the Overlapping Energy Regionfor an Efficient Intramolecular Energy Transfer: Functionalized Salen–Al/TriphenylamineGuest–Host Assemblies

A series of triphenylamine (TPA)-containing salen–Al assembly dyads, [salen(3-tBu-5-R)2Al(OC6H4-p-N(C6H5)2)] [salen = N,N′-bis(salicylidene)ethylenediamine; R = H (D1), tBu (D2), Ph (D3), OMe (D4), and NMe2 (D5)], were prepared in good yield (50–80%) and fully characterized by NMR spectroscopy and elemental analysis. Both the UV/vis absorption and photoluminescence (PL) spectra of D1–D4, except for D5, in a tetrahydrofuran solution exhibited dual patterns, which are assignable to the salen–Al-centered π–π* transition (low-energy region) and the TPA-centered π–π* transition (high-energy region). In particular, the emission spectra of the dyads displayed interesting dual-emissive patterns via a significant intramolecular energy transfer (IET) process between the salen–Al moiety and TPA group. Notably, this IET process was systematically tuned by varying the substituents and dominantly observed in the rigid state. More interestingly, compared to the salen–Al complexes (A1–A4) without the TPA group, D1–D4 exh...