title: Enhanced π-conjugation and emission via icosahedral carboranes: synthetic and spectroscopic investigation.
abstract: The ability of ortho-, meta- and para-carboranes to enhance the emission intensity has been compared. For this purpose a series of carborane-appended 1,3,5-triphenylbenzene (TB) and 1,3,5- tris(biphenyl-4-yl)benzene (TBB) containing three ortho-, meta- and para-carborane clusters directly attached to the conjugated cores have been synthesized employing Suzuki, Heck, and trimerization reactions. The incorporation of the icosahedral carboranes was associated with a red shift in the UV absorption spectrum of up to 13 nm as well as enhancements of the emission intensities of up to 154%. The presence of ortho-carboranes showed the maximum red shift in the UV spectrum whereas the maximum enhancement of the emission intensity was observed in the presence of meta-carborane clusters. The order of π-conjugation extension is found to be ortho > meta ≈ para. A comparative thermal analysis indicated o-carborane-appended trimers to be the most thermally stable in the series. Proton NMR spectra of reported carborane-appended trimers indicated that ortho- and meta-carborane cages have benzenelike characteristics.
authors: Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, Illinois 60115-2862, USA.
authors: Barada Prasanna
authors: BP
authors: Dash
authors: Rashmirekha
authors: R
authors: Satapathy
authors: Elizabeth R
authors: ER
authors: Gaillard
authors: Kathleen M
authors: KM
authors: Norton
authors: John A
authors: JA
authors: Maguire
authors: Neha
authors: N
authors: Chug
authors: Narayan S
authors: NS
authors: Hosmane