Electronic absorption and emission spectral data and fluorescence quantum yields of bridgedp-oligophenylenes, bi- to deciphenyls, and related furans and carbazoles

Abstract

Absorption and fluorescence emission spectral data, as well as fluorescence quantum yields (Φ_f), were determined for 41p-oligophenylene compounds containing 2–6, 8, and 10 benzene rings. Of 29 compounds containing carbon-bridged rings (fluorenes), 28 were dialkylated on each bridge for improved solubility and photostability. Absorption maxima for oligophenylenes were observed at wavelengths as long as 366 nm, emission maxima to 437 nm, and molar extinction coefficients (ɛ) as large as 153,000 L/mol-cm; all three exceeded predicted maximum values for the corresponding unbridged oligophenylenes. The substitution of furan for benzene or carbazole for a fluorene (two examples each) bathochromically shifted absorption and emission maxima. Dialkylated carbon bridges bathochromically shifted absorption and emission maxima, and lowered Φ_f in biphenyl and in one terphenyl analogue, but appeared to cause no diminution of Φ_f in higher oligophenylenes. Bis(2-methoxyethyl) substitution on the bridges, incorporated to provide solubility in polar solvents, lowered Φ_f in all examples. Tertiary alkyl substituents on terminal rings bathochromically shifted the absorption and emission maxima and generally increased Φ_f. The “loose bolt” effect, which lowers Φ_f in mononuclear substituted benzenes, may operate in 9,9-dialkylfluorenes, but not in 2,7-di-t-butylfluorene or in higher oligophenylenes. Cyclic ether and methoxy substituents as auxofluors on terminal rings generally bathochromically shifted absorption and emission maxima and increased ɛ and Φ_f. Cyano substituents bathochromically shifted absorption and emission maxima, and increased ɛ, but lowered Φ_f slightly.