Comparison of luminescent properties of helicene-like bibenzothiophenes with o-carborane and 5,6-dicarba-nidodecaborane

This article describes comparison of the anchoring effect on electronic properties of the helicene-like bibenzothiophene between o-carborane and 5,6-dicarba-nido-decaborane. The o-carborane and nido-decaborane-fused bibenzothiophenes were simultaneously obtained in the same reaction and successfully isolated. Initially, the X-ray single crystal analysis revealed that the helicene-like distorted structure was realized in the nido-decaborane-fused bibenzothiophene. From optical measurements in the solution state, distinct different characteristics depending on the type of anchors were observed. It was summarized that the absorption and luminescent properties originated from weak π-conjugation at the bibenzothiophene moiety in the o-carboranefused compound were obtained, whereas robust π-conjugation and significant emission from the intramolecular charge transfer state were detected from the nido-decaborane-fused compound. These data can be explained by the theoretical results that π-conjugation was restrictedly developed within the bibenzothiophene moiety in frontier orbitals of the o-carborane-fused compound. In contrast, π-conjugation can be constructed even through the distorted bibenzothiophene because of the nido-decaborane unit. Moreover, the intramolecular charge transfer state should be realized because of electronic interaction involving the nido-decaborane unit in the excited state. Furthermore, it was demonstrated that the nido-decaborane-fused compound possessed solid-state emission and mechanochromic luminescent properties. The π-conjugation on the distorted structure supported by the nido-decaborane anchor should play a significant role in suppressing aggregation-caused quenching followed by presenting solid-state emission with stimuli responsiveness.

Rational design for thermochromic luminescence in amorphous polystyrene films with bis-o-carborane-substituted enhanced conjugated molecule having aggregation-induced luminochromism

We designed the triad molecule,bis-o-carborane-substituted bis(thienylethynyl)benzene,as a filler for realizing thermochromic luminescent behaviors based on conventional polymer films,such as polystyrene.From the optical measurements,it was found that the triad can show solid-state emission and dual-luminescent properties with variable intensity ratios depending on media.From the mechanistic studies including the experiments with the methyl-substituted model compound,it was revealed that dual emission should be originated from the locally excited and twisted intramolecular charge transfer states,and the latter emission band is significantly enhanced in the solid states.We prepared amorphous films containing variable concentrations of the triad with the spin-coating method and investigated optical properties.It was found that intensity ratios were drastically changed by altering the concentration of the triad.By increasing the proportion of the triad,aggregation occurred,and emission color was apparently varied through the changes in intensity ratios of the dual emission property.Based on the aggregationinduced luminochromic property of the triad,thermochromic luminescence was finally realized by heating the amorphous films.The rational design for obtaining thermochromic luminescent amorphous films is illustrated in this paper.