title: Blue-shifted emission and enhanced quantum efficiency viaπ-bridge elongation in carbazole-carborane dyads.
abstract: Carbazole-carborane linear dyads and di(carbazole)-carborane V-shaped dyads with phenyleneethynylene-based bridges have been synthesized. The V-shaped dyads display the expected red-shifts in the location of their UV-Vis absorption maxima on bridge-lengthening, but show unusual blue-shifts in charge-transfer (CT) emission on the same π-system lengthening. These blue-shifts can be attributed to the 2n + 3 electron count within the carborane cluster in the excited state. The linear dyads luminesce via a combination of local excited (LE) and CT emission, with a red-shift in LE emission and a blue-shift in CT emission accompanying π-bridge elongation. A quantum efficiency as high as 86% in the solution state is achieved from the hybrid LE/CT emission. Time-dependent density functional theory (TD-DFT) calculations at the excited state of these compounds have clarified the photoluminescence blue-shift and suggested a typical cluster C-C bond elongation in the V-shaped dyads. Calculations on the elongated linear dyads have suggested that the electron density is localized at the phenyleneethynylene-containing bridge.
authors.affiliation: School of Chemical and Material Engineering, Jiangnan University, Wuxi 214122, Jiangsu Province, China. mark.humphrey@jiangnan.edu.cn.
authors.forename: Zhaojin
authors.initials: Z
authors.lastname: Wang
authors.forename: Peng
authors.initials: P
authors.lastname: Jiang
authors.forename: Tianyu
authors.initials: T
authors.lastname: Wang
authors.forename: Graeme J
authors.initials: GJ
authors.lastname: Moxey
authors.forename: Marie P
authors.initials: MP
authors.lastname: Cifuentes
authors.forename: Chi
authors.initials: C
authors.lastname: Zhang
authors.forename: Mark G
authors.initials: MG
authors.lastname: Humphrey