Efficient crystallization-induced emission in fluorenyl-tethered carboranes

Abstract

Fluorenyl-tethered o-carborane derivatives (Fl-Cb) as both mono- and di-aryl Cb assemblies were synthesized from the corresponding alkyne and BH(EtS) in ca. 60% yields. Crystallographic studies of di-aryl examples show rigid head-to-tail or tail-to-tail packing, while for the mono-aryl examples, only loose packing was observed. In solution, the Fl-Cb compounds exhibit strong quenching of their emission, while aggregation in a mixed solvent results in an enhanced, but still weak, emission [0.11 quantum efficiency (Φ)]. Crystallization-induced emission was observed with the di-aryl examples [Φ up to 0.95]. The excitation spectra are broadened, consistent with considerable orbital degeneracy within the crystals. Theoretical calculations suggest that the inherent orbital degeneracy and the highly-ordered crystalline aggregates contribute to the excellent crystallization-induced emission in these Fl-Cb compounds.

Photoluminescence in m-carborane–anthracene triads: a combined experimental and computational study

“…This difference could be the reason of the lower quantum yield in aggregate state in case of 6 comparing with 4 and 5, since the higher density of electronic states in case of 4 and 5 and the significant delocalization of the unoccupied orbitals between the molecules allow relaxation from higher-lying excited states via lower excited states (internal conversion), thus the emission will dominate instead of the non-radiative processes. 94 Thus, the DFT calculations support the idea that the different packing in the crystal structure of 6 causes the lower quantum yield. In contrast to the supramolecular structures of 4 and 5 ( Figure 1), in which each anthracene unit has two neighboring anthracenes from other molecules which are roughly parallel, dimers of 6 are packed twisted.…”

Modulation of the cis‐ and trans‐Conformations in Bis‐o‐carborane Substituted Benzodithiophenes and Emission Enhancement Effect on Luminescent Efficiency by Solidification

“…Even though intense luminescence can be observed in the solution state, optical properties were often spoiled through ACQ by intermolecular interactions in the solid state. [5][6][7] It has been reported that some of the o-carborane [8][9][10][11][12][13] derivatives presented AIE [14][15][16][17][18][19][20][21] and can be applied as a solid-state luminescent material. [1][2][3] Intense solid-state luminescent properties originating from AIE were found and applied for developing the conjugated materials, including polymers.…”

“…[4] Additionally, based on environment-responsive intensity changes of the AIE-active materials, various types of film-type luminescent materials and sensors can be fabricated. [5][6][7] It has been reported that some of the o-carborane [8][9][10][11][12][13] derivatives presented AIE [14][15][16][17][18][19][20][21] and can be applied as a solid-state luminescent material. [22][23][24][25][26][27][28][29][30][31][32][33][34] We have also focused on the arylmodified o-carboranes as a scaffold for constructing luminescent "element-block", [35,36] which is defined as a minimum functional unit composed of heteroatoms.…”

Enhancement of Aggregation-Induced Emission by Introducing Multiple o-Carborane Substitutions into Triphenylamine

“…Indeed, applicability of the modified o -carboranes for organic light-emitting devices has been demonstrated from the recent studies [ 30 , 31 ]. Moreover, it should be noted that some of the modified o -carboranes also showed AIE [ 23 , 24 , 30 , 32 , 33 , 34 , 35 , 36 , 37 , 38 ]. In the solution state, the modified o -carboranes presented slight emission as a result of emission annihilation by molecular motions, while intense emission was recovered because of low mobility in the solid state.…”