Synthesis, characterization, and optical properties of a cyano-functionalized 2,3,7,8-tetraaryl-1,6-dioxapyrene

2,7-Di(4-cyanophenyl)-3,8-di(4-methylphenyl)-1,6-dioxapyrene (CN-diox), a symmetrically substituted 2,3,7,8-tetraaryldioxapyrene, was synthesized in seven steps from 1,5-dihydroxynaphthalene. The synthetic methodology incorporated a base-catalyzed ring closure process followed by dehydration to introduce the first tetraaryl-1,6-dioxapyrene. Crystal structure and electrochemical analysis were performed to directly compare the properties of CN-diox to previously reported dioxapyrene derivatives, specifically 1,6-dioxapyrene (Diox) and 3,8-diethyl-5,10-dimethyl-1,6-dioxapyrene (Alkyl-diox). Optical spectroscopy studies were performed to evaluate the potential of the 1,6-dioxapyrenes as fluorescent probes. CN-diox revealed a broad absorption centered near 450 nm (ɛ = 31,900 M−1 cm−1) in THF with a corresponding fluorescence at 619 nm (Φf = 0.011). This was in sharp contrast to both Diox and Alkyl-diox which displayed broad absorption bands near 400 nm (ɛ ∼ 5000-10,000 M−1 cm−1) in THF with corresponding fluorescence near 500 nm (Φf = 0.059 and 0.082 for Diox and Alkyl-diox, respectively). The luminescence of CN-diox was found to be solvatochromic (λmax = 619-644 nm) with single exponential lifetimes of less than 1.3 ns and an excited state dipole moment of ∼22.81 D. Neither Diox nor Alkyl-diox showed solvatochromic properties.