AIE Active Carbazole-Benzothiazole Based ESIPT Motifs: Positional Isomers Directing the Optical and Electronic Properties

Abstract

Three positional isomers based on carbazole (Cz) and hydroxy benzothiazole (HBT) were synthesized targeting solid state organic emitters by Suzuki coupling reaction and their optical, structural and electronic properties were compared. The changing of position of HBT unit on 9‐phenyl‐9H‐carbazole alters the optical and structural properties significantly. The synthesized compounds are highly emissive in solid and aggregated state (Φf=∼ 40 %) and weakly emissive in solvents of different polarities (Φf=2.6‐17 %). The difference in the fluorescence quantum efficiency among the positional isomers can be assigned to conformational differences which were further supported by geometrical parameters computed by DFT computations. The present Cz‐HBT based ESIPT motifs are endowed with aggregation induced emission (AIE), solid state and polarity sensitive emission with large Stokes shift.

Water‐Assisted Emission Enhancement of 2‐Hydroxynaphthaldoxime and Related Compounds

“…Certain 2‐naphthol tethered Schiff bases show fluorescence emissions due to excited state intramolecular proton‐transfer and the intensity of emission in each case was enhanced upon addition of water. It is also suggested that ESIPT and AIE took place in those hydroxy‐aromatic imines and the emissions were dependent on the concentration of water . Based on these one may suggest that the emission occurring at the 446 nm of 2‐hydroxynaphthaldoxime upon addition of water is due to a combine effect of ESIPT and AIE.…”

ESIPT‐based AIE luminogens: Design strategies, applications, and mechanisms

“…Another widely used backbone that is used to construct ESIPT‐based AIEgens is 2‐(2′‐hydroxyphenyl)benzothiazole (HBT, Scheme 2I with X = S), which is a typical ESIPT fluorophore bearing an intramolecular hydrogen bond O─H···N and show AIE properties by virtue of RIM mechanism. [ 31, 36, 42, 45, 46, 56, 59, 63, 73, 76, 81, 100, 103, 108, 120–123, 126, 131 , 180–194 ] The emissions of HBT derivatives are easily tunable and extended to the red region, making them advantageous to be applied in bioimaging. [ 103, 126, 192, 193, 195 ] In addition, a few of ESIPT‐based AIEgens based on 2‐(2′‐hydroxyphenyl)benzimidazole (HBI, Scheme 2I with X = NH), [ 196 ] and 2‐(2′‐aminophenyl)benzothiazole (ABT, Scheme 2J) [ 52, 63, 90, 101, 114, 197 ] have been reported.…”

Recent Trends in the Design, Synthesis, Spectroscopic Behavior, and Applications of Benzazole-Based Molecules with Solid-State Luminescence Enhancement Properties

“…They are strongly emissive in the green region. The PLQY reaches 0.38 for 47, but is lower for the other two compounds, due to conformational differences [75]. [75], 50 [52], 51 [77] and 52 [78] with solid-state PL maxima (λ em ) and photoluminescence quantum yields (Φ PL ).…”

“…Figure 15. Molecular structure of carbazole derivatives 47−49[75], 50[52], 51[77] and 52[78] with solid-state PL maxima (λ em ) and photoluminescence quantum yields (Φ PL ).…”