DOI: 10.1002/chem.201402396

Two sets of o-carborane derivatives incorporating fluorene and anthracene fragments as fluorophore groups have been successfully synthesized and characterized, and their photophysical properties studied. The first set, comprising fluorene-containing carboranes6–9, was prepared by catalyzed hydrosilylation reactions of ethynylfluorene with appropriate carboranylsilanes. The compound 1-[(9,9-dioctyl-fluorene-2-yl)ethynyl]carborane (11) was synthesized by the reaction of 9,9-dioctyl-2-ethynylfluorene and decaborane (B₁₀H₁₄). Furthermore, reactions of the lithium salt of 11 with 1 equivalent of 4-(chloromethyl)styrene or 9-(chloromethyl)anthracene yielded compounds 12 and 13. Members of the second set of derivatives, comprising anthracene-containing carboranes, were synthesized by reactions of monolithium or dilithium salts of 1-Me-1,2-C₂B₁₀H₁₁, 1-Ph-1,2-C₂B₁₀H₁₁, and 1,2-C₂B₁₀H₁₂ with 1 or 2 equivalents of 9-(chloromethyl)anthracene, respectively, to produce compounds 14–16. In addition, 2 equivalents of the monolithium salts of 1-Me-1,2-C₂B₁₀H₁₁ (Me-o-carborane) and 1-Ph-1,2-C₂B₁₀H₁₁ (Ph-o-carborane) were reacted with 9,10-bis(chloromethyl)anthracene to produce compounds 17 and 18, respectively. Fluorene derivatives 6–9 exhibit moderate fluorescence quantum yields (32–44 %), whereas11–13, in which the fluorophore is bonded to the C_cluster (C_c), show very low emission intensity (6 %) or complete fluorescence quenching. The anthracenyl derivatives containing the Me-o-carborane moiety exhibit notably high fluorescence emissions, with ϕ_F=82 and 94 %, whereas their Ph-o-carborane analogues are not fluorescent at all. For these compounds, we have observed a correlation between the C_cC_c bond length and the fluorescence intensity in CH₂Cl₂ solution, comparable to that observed for previously reported styrene-containing carboranes. Thus, our hypothesis is that for systems of this type the fluorescence may be tuned and even predicted by changing the substituent on the adjacent C_c. Prof. Dr. Francesc Teixidor