Temperature-Controlled Locally Excited and Twisted Intramolecular Charge-Transfer State-Dependent Fluorescence Switching in Triphenylamine–Benzothiazole Derivatives

Abstract

Triphenylamine–benzothiazole derivatives, N -(4-(benzo[ d ]thiazol-2-yl)phenyl)- N -phenylbenzenamine ( 1 ), N -(4-(benzo[ d ]thiazol-2-yl)-3-methoxyphenyl)- N -phenylbenzenamine ( 2 ), and 2-(benzo[ d ]thiazol-2-yl)-5-(diphenylamino)phenol ( 3 ), showed unusual temperature-controlled locally excited (LE) and twisted intramolecular charge-transfer (TICT) state fluorescence switching in polar solvents. The detailed photophysical studies (absorption, fluorescence, lifetime, and quantum yield) in various solvents confirmed polarity-dependent LE and TICT state formation and fluorescence tuning. 1 and 2 exhibited strong fluorescence with short lifetime in nonpolar solvents compared to polar solvents. 1 , 2 , and 3 in dimethylformamide (DMF) at room temperature showed low-energy weak TICT state fluorescence, whereas high-energy strong LE state fluorescence was observed at −196 °C. Interestingly, further increasing the temperature from 20 to 100 °C, the DMF solution of 1 and 2 exhibited rare fluorescence enhancement with a slight blue shift of λ max via activating more vibrational bands of the TICT state. Thus, 1 and 2 showed weak TICT state fluorescence at room temperature, strong LE state fluorescence at −196 °C, and activation of TICT state at 100 °C. Moreover, molecular conformation and aggregation in the solid state influenced strongly on the fluorescence properties of 1 , 2 , and 3 . Solid-state fluorescence and pH-responsive imidazole nitrogen have been exploited for demonstrating halochromism-induced fluorescence switching. Computational studies provided further insights into the fluorescence tuning and switching. The present studies provide understanding and opportunity to make use of D–A organic molecules in the LE and TICT states for achieving fluorescence switching and tuning.

Effects of polyimide curing on image sticking behaviors of flexible displays

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Ultrafast Excited State Relaxation Dynamics of New Fuchsine‐ a Triphenylmethane Derivative Dye

“…Similar observations were reported for triphenylamine À benzothiazole derivatives where temperature-controlled locally excited and TICT-dependent fluorescence switching was observed. [57] To understand the effect of ring rotation in the molecule, fluorescence anisotropy measurements were carried out for NF solution at room temperature and for NF film at both room temperature and 77 K. The steady-state fluorescence anisotropy has been measured using the same FLS1000 spectrofluorometer operating in L-format, fitted with polarizers in both the excitation and emission arms. To calculate the emission anisotropy, the polarizers in the excitation and emission channels were rotated to vertical (V) and horizontal (H) positions, and by doing their combination four intensities were measured:…”

Phenanthroimidazole-based bipolar carbazoles featuring cyano substituents to realize efficient deep-blue electroluminescence with an external quantum efficiency of nearly 6%

“…17,18 The locally excited component offers efficient radiative fluorescence decay due to a large transition moment, while the charge transfer excited state allows small energy splitting between singlet and triplet states for efficient reverse intersystem crossing (RISC) process in higher-lying excited states. 19,20 Thus, using HLCT materials as the emitter in OLED devices may provide better EL performance. 21 As observed in the literature, the incorporation of cyano groups in the molecular framework increases the charge transfer (CT) characteristics in the excited state.…”