Excitation spectroscopic and synchronous fluorescence spectroscopic analysis of the origin of aggregation-induced emission in N,N-diphenyl-1-naphthylamine-o-carborane derivatives

Abstract

We have synthesised mono-(NpCb) and bis-[(N,N-phenyl-1-naphthylamino)benzo]-o-caboranes (NpCbNp), which show anomalously intense aggregation-induced emission (AIE) at long wavelengths and monomer emission at short wavelengths. The actual concentration of the aggregator in intense AIE is very low, so absorption spectroscopy is unsuitable for detecting small changes in the absorbance. Hence, to understand the aggregation pattern, we employ excitation spectroscopy, since this method has excellent sensitivity in compliance with the emission intensity. Moreover, we carried out synchronous fluorescence spectroscopic measurements to confirm that the aggregator is different from the monomeric species. The excitation spectrum shows distinguishable differences between the AIE and the normal emission. For the triad NpCbNp, the excitation spectrum for the AIE is located at a shorter wavelength than that for the monomeric emission spectrum, which means that the AIE is attributed to the H-type aggregator. On the other hand, for the dyad NpCb, the excitation spectrum for the AIE is observed at an identical wavelength as that for the monomeric species, which indicates that the aggregator is of the oblique type.

Recent Progress in the Development of Solid‐State Luminescent o‐Carboranes with Stimuli Responsivity

“…Kang et al. synthesized the series of TPA‐substituted o ‐carboranes 2 – 9 and carefully investigated the origin of AIE using transient absorption spectroscopy and synchronous fluorescence spectroscopy . It is noteworthy that ICT involving the o ‐carborane unit and the aryl moiety should play an important role in AIE.…”

Highly Deformedo‐Carborane Functionalised Non‐linear Polycyclic Aromatics with Exceptionally Long C−C Bonds

“…Whenever molecular motion is restricted, however, carboranyl ICT states become more radiative. This often occurs upon aggregation, in a process known as aggregation induced emission (AIE) [7, 17, 18, 20–39] . o ‐Carborane is therefore considered an ‘AIE‐active element block’ [40]…”

“…This often occurs upon aggregation,i naprocess knowna sa ggregationi nduced emission (AIE). [7,17,18,[20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] o-Carborane is therefore considered an 'AIE-active element block'. [40] The AIE efficiency in carborane-containing fluorophores is enhanced when the rotation of the carboranei ss tructurally restricted around the ICT geometry (i.e.,w hen the C C ÀC C bond is approximately perpendicular to plane of the fluorophore).…”

Effect of Planarity of Aromatic Rings Appended to o-Carborane on Photophysical Properties: A Series of o-Carboranyl Compounds Based on 2-Phenylpyridine- and 2-(Benzo[b]thiophen-2-yl)pyridine

“…Such a good conjugated system results in intramolecular charge transfer (ICT) transition between the two components [29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51]. Thus, the unprecedented luminescent properties of numerous o -carboranyl compounds emerge from the ICT-based emissive features [29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57]. For those reasons, o -carborane-containing organic and organometallic luminophores have been extensively spotlighted in optoelectronic research fields.…”