Molecular Engineering of Triphenylamine Based Aggregation Enhanced Emissive Fluorophore: Structure-Dependent Mechanochromism and Self-Reversible Fluorescence Switching

Abstract

Triphenylamine (TPA), a propeller-shaped optoelectronic molecule, has been used to generate stimuli-responsive smart fluorescent organic materials and correlate the effect of subtle structural changes on the molecular packing and mechanochromic fluorescence (MCF). The substituent (OCH3) position in the TPA phenyl ring and acceptors (malononitrile, cyanoacetamide, cyanoacetic acid, ethyl cyanoacetate, and diethylmalonate) strongly influenced the solid state and mechanochromic fluorescence as well as the molecular packing. The structure–property studies revealed that (i) TPA derivatives without the OCH3 substituent exhibit strong fluorescence (Φf = 85% (TCAAD-1, 55% (TDEM)), (ii) higher dihedral angle (τ) between donor (aminophenyl) and acceptor lead to weak/non fluorescent material, (iii) substituent at the ortho position to acceptor increased the dihedral angle (τ = 26.49 (TCAAD-2), τ = 27.14 (TDMM)), and (iv) the increase of alkyl groups produced self-reversible high contrast off-on fluorescence switching materials (TDEM). Powder X-ray diffraction studies indicate that stimuli induced reversible phase transformation from crystalline to amorphous and vice versa was responsible for fluorescence switching. The computational studies also supported that OCH3 substitution at ortho to acceptor increased the dihedral angle and optical band gap. Thus, the present studies provide a structural insight for designing TPA based organic molecules for developing new smart organic materials.

Pressure‐Induced Wide‐Range Reversible Emission Shift of Triphenylamine‐Substituted Anthracene via Hybridized Local and Charge Transfer (HLCT) Excited State

“…By contrast, no obvious peaks were observed after grinding, suggesting that the ground solid is amorphous with a poorly organized structure . With time, sharp and intense peaks are recovered and they are perfectly coincided with patterns of the original solid, which illustrates that the blue‐shifting of the ground TPA‐AN crystal is introduced by the structural transformation from crystalline to amorphous state . Also, the self‐recovery of TPA‐AN powder may be attributed to the highly crystalline nature of the original TPA‐AN crystal.…”

“…Various strategies for molecular designs and structural modifications have been tried to change the luminescent features of the D‐A molecules, aiming at the broad‐range and full‐color emission . One of possible ways is considered to apply external forces for the twist intramolecular charge transfer (TICT) state and the HLCT excited state, switching the photoluminescence band in a certain spectral range . By reviewing literatures, the tunable ranges of individual emission band of the MCF materials are limited, as listed in Table 1 .…”

Development of Polyamine‐Substituted Triphenylamine Ligands with High Affinity and Selectivity for G‐Quadruplex DNA

“…Computational method:M olecular dynamics (MD) studies started with the construction of the TPA-3P and TPA3PY ligands, from the basic structure reported by Hariharan et al [21] (CCDC code: 1448378) for the TPAm oiety,a nd completing the ligand structures with the help of xleap software. The degree of protonation of TPA3P and TPA3PY was approximated to seven in both cases, taking into account the calculated protonation constants.…”

Easily Accessible Schiff Base ESIPT Molecules with Tunable Solid State Fluorescence: Mechanofluorochromism and Highly Selective Co2+ Fluorescence Sensing

“…Aggregation caused quenching effect makes strongly solution fluorescent π‐conjugated organic molecules into non‐fluorescence in the solid state . Discovery of aggregation enhanced emissive (AEE) phenomena in non‐planar molecular structure via supramolecular interactions mediated rigidification of intramolecular rotation produced enhanced emissive solids . On the other hand, excited state intramolecular proton transfer (ESIPT) mechanism lead to strong fluorescence in the solid state from planar π‐conjugated molecules .…”