Excited‐State Intramolecular Proton‐Transfer Properties of Three Tris(N‐Salicylideneaniline)‐Based Chromophores with Extended Conjugation

• Published in: Chemistry : a European journal 2017-01, Vol.23 (4), p.917-925
• Main Authors: Jagadesan, Pradeepkumar, Whittemore, Tyler, Beirl, Toni, Turro, Claudia, McGrier, Psaras L.
• Format: Article
• Language: English
• Subjects: Chemistry; Conjugation; Copper; Excitation spectra; Femtosecond; fluorescence; Metal ions; metal sensing; Olefins; photochemistry; proton transfer; Solid state; Synthesis
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201604315

The synthesis and photophysical properties of three tris(N‐salicylideneaniline) (TSA) compounds containing 1,3,5‐triarylbenzene, ‐tristyrylbenzene, and ‐tris(arylethynyl)benzene core units are reported. The TSA compounds underwent efficient excited‐state intramolecular proton transfer (ESIPT) in solution and in solid state due to the preformed C=N⋅⋅⋅H−O hydrogen‐bonded motifs of the structures. Steady‐state fluorescence emission spectra of the TSA molecules revealed dual bands only in DMSO, and large Stokes shifts in other polar aprotic and protic solvents. Femtosecond transient absorption spectroscopic measurements in THF revealed lifetime values in the range of 14–16 ps for the excited‐state keto‐tautomer. The TSA compounds are also responsive to metal ions (Cu2+ and Zn2+) in DMSO, exhibit enhanced aggregate‐induced emission (AIE) properties in DMSO/water mixtures, and are highly luminescent in the solid state. Excited‐State Properties: Three C3‐symmetric tris(N‐salicylideneaniline) (TSA) compounds containing 1,3,5‐triarylbenzene, ‐tristyrylbenzene, and ‐tris(arylethynyl)benzene core units were synthesized, and their excited‐state intramolecular proton‐transfer (ESIPT) properties were evaluated. The introduction of alkene and alkyne linker units between the central benzene and the SA units has a considerable effect on their absorbance spectra, but a minimal effect on their ESIPT properties in solution (see scheme). The TSA compounds are responsive to metal ions (Cu2+ and Zn2+) in DMSO and highly luminescent in the solid state.