Synthesis of Aggregation-Induced Emission Based Tetraphenylethylene Conjugated Sulfonamide and Sulfonate Ester: Single-Crystal X-Ray Diffraction Evaluation, Photophysical Characteristics, Self-Assembly, and Exploring Invisible Ink Applications

Abstract

Aggregation-induced emission (AIE) active organic compounds have received significant attention owing to their superior emission properties in aggregate and solid states, which are useful in advanced material applications such as bioimaging, chemo-biosensing, optoelectronics, data security, and anti-counterfeiting. Herein, AIE-based tetraphenylethylene conjugated sulfonamide (TPE-NTS) and sulfonate ester (TPE-OTS) have been synthesized. Single-crystal X-ray diffraction analysis was carried out to determine molecular structure of TPE-NTS and TPE-OTS, and to visualize the intermolecular interactions that occur in the solid state. The TPE-NTS formed aggregation in dimethyl sulfoxide (DMSO) as the water content grew from 60% to 90%, resulting in the formation of a new emission peak at 471 nm. Conversely, when the water content in DMSO was increased from 50% to 90%, the TPE-OTS aggregation caused a new emission peak at 464 nm. The naked-eye visualization also demonstrated that TPE-NTS and TPE-OTS were AIE-active in increasing water percentage in DMSO. The optical microscope and scanning electron microscopy analysis revealed that in 70% and 90% water fractions in DMSO, TPE-NTS formed several micrometers-long ordered flake-like self-assembled structures, whereas TPE-OTS generated well-ordered micro-rods containing flower-like self-assembled structures. Calculations using density functional theory and time-dependent density functional theory showed the photophysical behavior of both TPE-NTS and TPE-OTS. The invisible inks made from TPE-NTS and TPE-OTS were inactive in daylight but activated when exposed to ultraviolet light. These invisible inks were tested for advanced anti-counterfeiting applications such as trademark document security.