Synthesis and luminescent properties of 4'-phenyl-2,2':6',2 double prime -terpyridyl compounds bearing different aryl substituents

A series of new 4'-phenyl-2,2':6',2 double prime -terpyridine compounds bearing different aryl substituents (Ar=phenyl (1a), 2,4-difluorophenyl (1b), 4-(trifluoromethyl) phenyl (1c), 4-methoxyphenyl (1d), 9-hexyl-9H-carbazolyl (1e), 9,9-dihexyl-9H-fluorenyl (1f), 4-(diphenylamino)phenyl (1g)) were synthesized and characterized. The influence of the aryl substituents on the luminescence of these compounds is systematically investigated by spectroscopic methods and simulated by density functional theory (DFT) calculations. All compounds exhibit structured absorption bands in the UV region; and broad, structureless charge-transfer bands/shoulders for 1d-1g, which systematically red-shifts when electron-donating substituents are introduced to the phenyl rings, but blue-shifts when electron-withdrawing substituents are attached on the phenyl rings. All compounds are emissive in solution at room temperature ( lambda emmax=358-489 nm, Phi sub(F)=0.16-0.92, tau sub(F)=0.77-2.24 ns), which can be attributed to super(1) pi , pi */ super(1)ICT (intramolecular charge transfer) state. Their fluorescent quantum yields increases when the electron-donating aryl substituents attached on the phenyl rings. DFT calculations on 1a-1g were also performed to gain insight into the nature of the ground electronic state. As the representative of compounds with electron-donating substituents, 1f exhibited high fluorescent quantum yields ( Phi sub(f) greater than or equal to 0.90 in solvents) while the compounds with electron-withdrawing substituents showed relative low fluorescent quantum yields. Their photophysical properties have been investigated with the aim to provide a basis for elucidating the structure-property correlations and developing new blue light-emitting materials.