Thaksen Jadhav

Mechanochromism and aggregation induced emission in benzothiazole substituted tetraphenylethylenes: a structure function correlation

The donor–acceptor benzothiazole substituted tetraphenylethylenes (BT-TPEs) 3a–3c were designed and synthesized to examine the effect of the linkage between the BT and the TPE unit on the photophysical, aggregation induced emission (AIE) and mechanochromic properties. The syntheses of BT-TPEs 3a–3c were achieved by the Pd-catalyzed Suzuki cross-coupling reaction of bromobenzothiazoles 1a–1c with 4-(1,2,2-triphenylvinyl)phenylboronic acid pinacol ester (2). The study showed that their photophysical, AIE and mechanochromic properties are dependent on the linkage between the BT and the TPE unit (ortho, meta, and para). The meta isomer 3b shows the highest grinding induced spectral shift (51 nm) whereas the ortho isomer 3a shows the lowest grinding induced spectral shift (9 nm). The single crystal X-ray structures reveal the highly twisted conformation and tight packing in BT-TPE 3a compared to 3b. The thermogravimetric analysis of BT-TPEs shows good thermal stability. The computational study reveals the donor–acceptor nature of the BT-TPEs. The structure–function correlation indicates that the mechanochromic and aggregation induced emission (AIE) properties were dependent on the linkage between BT and TPE.

Aggregation induced emission and mechanochromism in pyrenoimidazoles

Pyrene-based solid state emitters 3a and 3b were designed and synthesized by the Pd-catalyzed Suzuki cross-coupling reaction of bromopyrenoimidazole 2 with 4-(1,2,2-triphenylvinyl)phenylboronic acid pinacol ester and 2-(4-pinacolatoboronphenyl)-3,3-diphenylacrylonitrile. The single crystal X-ray structure of 3a was reported and revealed the twisted conformation. Their photophysical, aggregation induced emission (AIE) and mechanochromic properties were studied. Pyrenoimidazoles 3a and 3b exhibit strong AIE. 3b shows different colored emission with varying water fraction. 3a and 3b exhibit reversible mechanochromic behavior with color contrast between blue and green. The enhanced conjugation and increased amorphous nature observed after grinding are associated with mechanochromism in pyrenoimidazoles 3a and 3b.

Donor–Acceptor Ferrocenyl-Substituted Benzothiadiazoles: Synthesis, Structure, and Properties

This article reports the design, and synthesis of D-π1-A-π2-D unsymmetrical, and D-π1-A-π2-A-π1-D symmetrical type of ferrocenyl-substituted benzothiadiazoles by the Pd-catalyzed Sonogashira, and Stille coupling reactions. The photophysical and electrochemical behavior of the ferrocenyl-substituted benzothiadiazoles show strong donor-acceptor interaction. The increase in the number of acceptor benzothiadiazole unit, results in the lowering of the energy gap, which leads to the bathochromic shift of the absorption spectrum. The single crystal X-ray structures of 3a, 5a, and 5g were obtained which show interesting supramolecular interactions.

Effect of the cyano group on solid state photophysical behavior of tetraphenylethene substituted benzothiadiazoles

Two unsymmetrical tetraphenylethene (TPE) substituted Donor–Acceptor (D–A) benzothiadiazoles (BTDs) 3a, and 3b were designed and synthesized by the Suzuki cross-coupling reaction. The design strategy was opted to maintain the donor (TPE) fragment constant and the acceptor strength of BTD was modulated by using phenyl and cyanophenyl units. Their solvatochromism, aggregation induced emission (AIE) and mechanochromic properties were investigated. The BTDs 3a, and 3b exhibit strong solvatochromic and AIE behavior. The cyano-group containing BTD 3b exhibits reversible mechanochromic behavior with high color contrast between green and yellow, whereas 3a do not show mechanochromism. The solid state absorption and emission properties of BTDs 3a, and 3b show different behavior in their pristine and ground form. The powder XRD study shows a reversible morphological change between the crystalline and amorphous phase upon grinding.

Aggregation induced emission and mechanochromism in tetraphenylethene substituted pyrazabole

Tetraphenylethene (TPE) substituted pyrazabole 2 was designed and synthesized by the Pd-catalyzed Suzuki cross-coupling reaction. The pyrazabole exhibits strong aggregation induced emission (AIE) and reversible mechanochromic behavior with high color contrast between blue and green. The powder XRD studies show that destruction of crystalline state into amorphous state is responsible for mechanochromism.

meso-Aryloxy and meso-arylaza linked BODIPY dimers: synthesis, structures and properties

meso-Aryloxy and meso-arylaza linked BODIPY dimers have been designed and synthesized by the nucleophilic aromatic substitution (SNAr) type reactions of phenylenediamines (a, b, c) and phenylenediols (d, e, f) with 8-chloro BODIPY. The photophysical and electrochemical properties of the BODIPY dimers were found to be dependent on the nature of the heteroatom at the meso position on the BODIPY ligand and the substitution pattern of the BODIPYs on the phenyl ring (i.e. ortho, meta and para). The experimental observations were supported by theoretical calculations. The single crystal X-ray structures of 1, 2b, 2c and 3e are reported. The packing diagram of 1 reveals a herringbone like structural arrangement, whereas 2b, 2c and 3e show complex 3D structural motifs.

Mechanochromism and electroluminescence in positional isomers of tetraphenylethylene substituted phenanthroimidazoles

The study of aggregation-induced emission (AIE) luminogens has gained momentum due to their remarkable luminogenic properties and applications in mechano-sensors and organic light-emitting diodes (OLEDs). In this article we have studied three positional isomers (ortho, meta, and para) of phenanthroimidazoles 3a–3c and explored their AIE, mechanochromic and electroluminescence behavior. The phenanthroimidazoles 3a–3c were synthesized by the Suzuki cross-coupling reaction of (2-bromo/3-bromo/4-bromo)phenathroimidazoles 2a–2c with 4-(1,2,2-triphenylvinyl)phenylboronic acid pinacol ester in good yields. The phenanthroimidazoles 3a–3c exhibit strong AIE. The mechanochromic study reveals reversible mechanochromism with good color contrast between blue and green colors. The ortho (3a) and meta (3b) isomers exhibit a grinding induced spectral shift of 98 nm while the para-isomer (3c) exhibits a spectral shift of 43 nm. Moreover, 3a–3c were explored as non-doped blue emitters in efficient organic light-emitting diodes. Among the three emitters, 3c provided a high quantum efficiency of 4.0% in a non-doped blue device.

C 3 symmetric ferrocenyl triazines: synthesis, structure, and properties

A series of C3 symmetric ferrocenyl-substituted 1,3,5-triazines has been designed and synthesized by the Sonogashira cross-coupling reaction. The photophysical and electrochemical properties of these triazines show substantial donor–acceptor interaction. The single crystal X-ray structure of triazine 3 is reported, which shows a planar structure. The supramolecular structure of 3 exhibits intermolecular π–π interaction, which leads to the formation of 2D layered structures.

T-Shaped donor–acceptor–donor type tetraphenylethylene substituted quinoxaline derivatives: aggregation-induced emission and mechanochromism

Smart mechanofluorochromic materials are of great importance owing to their wide range of applications and have been effectively synthesized by incorporating aggregation-induced emission (AIE) active luminogens. In this contribution, we have synthesized two novel T-shaped D–A–D type luminophores, tetraphenylethylene (TPE) substituted acenapthene-quinoxaline 1 and TPE substituted phenanthrene quinoxaline 2, by the Suzuki cross-coupling reaction. Their solavatochromism, AIE and mechanochromism were evaluated. The D–A–D structured luminophores 1 and 2 show solvent-dependent intramolecular charge transfer (ICT) transitions, which were explored using solvatochromism, and also exhibit strong AIE behaviour. Luminophores 1 and 2 show highly reversible mechanochromism with a good colour contrast, which was further studied using photophysical properties, powder X-ray diffraction and theoretical calculations. The powder XRD study reveals a morphological change from crystalline to amorphous, which is responsible for mechanochromism.

Meso Alkynylated Tetraphenylethylene (TPE) and 2,3,3-Triphenylacrylonitrile (TPAN) Substituted BODIPYs.

The tetraphenylethylene (TPE) substituted BODIPY 2a, and 2,3,3-triphenylacrylonitrile (TPAN) substituted BODIPYs 2b and 2c were designed and synthesized by the Pd-catalyzed Sonogashira cross-coupling reaction. Their photophysical and electrochemical properties were investigated. The BODIPY 2a exhibits strong D-A interaction with poor fluorescence quantum yield. The BODIPYs 2b and 2c show red-shifted absorption and emission with higher fluorescence quantum yield compared to BODIPY 2a. The photonic properties of BODIPYs 2a-2c were compared with 4-ethynylbenzonitrile substituted BODIPY 3 and phenylacetylene substituted BODIPY 4. The results reveal that the electron donating group at the meso position of BODIPY blue shifts the absorption and emission with decreased fluorescence quantum yield, whereas the electron withdrawing group at the meso position of BODIPY red shifts the absorption and emission with enhanced quantum yields. The single crystal structures of BODIPYs 2a and 2b reflect the planar orientation of meso substituent and the BODIPY core, which leads to close π-π stacking. The extensive π-π stacking and strong donor-acceptor (D-A) interaction makes these BODIPYs AIE inactive. The experimental observations were supported by DFT calculation.