Synthesis and emitting properties of the blue-light fluorophores indolizino[3,4,5-ab]isoindole derivatives

Article abstract of DOI:10.1002/ejoc.200700250

Indolizino[3,4,5-ab]isoindoles 3a-3k have been synthesized by [8+2] cycloaddition reactions of the corresponding indolizines 2a-2k with benzyne in moderate yields. Cycloadditions of pyrrolo[2,1-a]isoquinolines 4a-4c with benzyne gave the benzo[6,7]pyrrolizino[3,4,5-ab]isoquinolines 5a-5c. Compounds 7 and 9 were similarly prepared by the reactions of 6H-[1]benzopyrano[3,4-a] indolizine-6-one (6) and 6H-[1]benzopyrano[3′,4′:3,4]pyrrolo[2,1-a] isoquinolin-6-one (8) with benzyne in 93 and 62 % yields, respectively. The electronic structures of these compounds have been calculated by the DFT method at the B3LYP/6-31G level. Compounds 3a-3j fluoresce in the blue region (λ_max^F = 439-475 nm) with high quantum yields (Φ_F = 0.49-0.77 in ethanol). Compounds 5a-5c and 9 are fluorescent in the green region with quantum yields of 0.44-0.77 in ethanol and compound 7 emits blue light with a quantum yield of 0.59. The electrochemical properties of these compounds have been investigated by cyclic voltammetry. Indolizino[3,4,5-ab]isoindoles without a substituent at C-2 (compounds 3a, 3c, 3d) or with an alkyl substituent in the framework (31, 3k) undergo irreversible anodic oxidations and reversible cathodic reductions. Compounds 3e and 3g with an electron-withdrawing group at C-2, on the other hand, undergo quasi-reversible oxidations at 1.2-1.3 V (SCE) and reversible reductions at -1.5 to -1.9 V (SCE). Therefore, compounds 3e and 3g may be promising candidates to serve as blue-light emitters with both hole- and electron-transporting ability in monolayer OLED devices, while the other indolizino[3,4,5-ab]isoindoles (3a-3d, 3f, 3h-3i) are potential blue-light emitters with electron-transporting ability. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.