Synthesis, Characterization, and Optical Properties of a Cyano-Functionalized 4,5,9,10-tetraaryl-l,6-dioxapyrene

Abstract

5,10-Di(4-cyanophenyl)-4,9-di(4-methylphenyl)-1,6-dioxapyrene ( CN-diox), a symmetrically substituted 4,5,9,10-tetraaryldioxapyrene, was synthesized in seven steps from 1,4-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 4,9-diethyl-2,7-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 (epsilon = 31,900/M/cm) in THF with a corresponding fluorescence at 619 nm (Phi(sub f) = 0.011). This was in sharp contrast to both Diox and Alkyl-diox which displayed broad absorption bands near 400 nm (epsilon approx. 5,000-10,000/M/cm) in THF with corresponding fluorescence near 500 nm (Phi(sub f) = 0.059 and 0.082 for Diox and Alkyl-diox, respectively). The luminescence of CN-diox was found to be solvatochromic (lambda(sub max) = 619 nm-644 nm) with single exponential lifetimes of less than 1.3 ns. Neither Diox nor Alkyl-diox showed solvatochromic properties