title: Fluorescence of new o-carborane compounds with different fluorophores: can it be tuned?
abstract: 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 carboranes 6-9, 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 %), whereas 11-13, in which the fluorophore is bonded to the Ccluster (Cc), 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 ϕF = 82 and 94 %, whereas their Ph-o-carborane analogues are not fluorescent at all. For these compounds, we have observed a correlation between the Cc-Cc 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 Cc.
authors: Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus U.A.B., 08193 Bellaterra, Barcelona (Spain).
authors: Albert
authors: A
authors: Ferrer-Ugalde
authors: Arántzazu
authors: A
authors: González-Campo
authors: Clara
authors: C
authors: Viñas
authors: Jesús
authors: J
authors: Rodríguez-Romero
authors: Rosa
authors: R
authors: Santillan
authors: Norberto
authors: N
authors: Farfán
authors: Reijo
authors: R
authors: Sillanpää
authors: Antonio
authors: A
authors: Sousa-Pedrares
authors: Rosario
authors: R
authors: Núñez
authors: Francesc
authors: F
authors: Teixidor
keywords: anthracene; carboranes; fluorene; fluorescence; photoluminescence