A small change in molecular structure, a big difference in the AIEE mechanism

Abstract

An anthracene carboxamide derivative of the excited-state intramolecular proton-transfer compound of 2-(2'-hydroxyphenyl)benzothiazole has been newly developed to produce the prominent characteristics of aggregation-induced enhanced emission (AIEE) with a high solid-state fluorescence quantum efficiency of 78.1%. Compared with our previously reported phenyl carboxamide derivatives, a small tailoring of the molecular structure was found to result in a big difference in the dominant factor of the AIEE mechanism. In the phenyl carboxamide derivatives, the dominant factor of the AIEE mechanism is the restriction of the twisted intramolecular charge transfer (TICT) of the enol excited state, regardless of their different aggregation modes. In the anthracene carboxamide derivative, N-(3-(benzo[d]thiazol-2-yl)-4-hydroxyphenyl) anthracene-9-carboxamide, the AIEE characteristics are not dependent on the restriction of TICT, but mainly attributed to the cooperative effects of J-aggregation and the restriction of the cis-trans tautomerization in the keto excited state. A specific N···π interaction was found to be the main driving force for this J-aggregation, as revealed by the single crystal analysis. The AIEE mechanism of this anthracene carboxamide derivative was studied in detail through photophysical investigations and theoretical calculations. On the basis of its AIEE characteristics, a stable non-doped organic light-emitting diode was achieved, with high color purity and a remarkably low efficiency roll-off.

π–π Interactions: Influence on Molecular Packing and Solid‐State Emission of ESIPT and non‐ESIPT Motifs

“…The short wavelength ( λ em =465 nm) and long wavelength emission ( λ em =527 nm) can be assigned to the excited state cis ‐enol and cis ‐keto tautomers, respectively . The dual emission in the solid state for ESIPT compound could be due to restriction of cis ‐ trans transformation of the keto form in the excited state due to tight molecular packing . In the solid state, an intramolecular hydrogen bond dominates over intermolecular hydrogen bonding due to physical constraints resulting into an ESIPT process .…”

Gels with sense: supramolecular materials that respond to heat, light and sound

“…318 The emissions of solid anils are often amplified due to the increased stability of the cis-keto structure, alongside more general AIEE effects such as J-aggregation, restricted conformational freedom and the prevention of TICT states. 321 A further notable characteristic of anils in the solid state, and crystals in particular, is their variable susceptibility to isomerisation. Anils prone to tautomerisation upon heating are more likely to adopt planar conformations, which localise electron density on the nitrogen atom by minimising π-π overlap with the adjacent aniline ring.…”

Nanoparticles of Conjugated Molecules and Polymers for Biomedical Applications

“…They have been shown to possess unique photophysical properties that differ from those of typical fluorescent organic dyes. In the isolated solution state, fluorescence is unusually quenched as a result of formation of nonplanar geometries with torsional freedom, whereas their emission is greatly enhanced by solidification as a result of restricted torsional motion and minimized quenching interaction [42]. Thus, they can maintain bright fluorescence in concentrated or aggregated states without typical aggregation-induced fluorescence quenching.…”