Structural Configuration and Molecular Motion-Assisted Emission Switching from Condensed Nanoaggregates to Macrocrystals: Rewritable Encryption and Photosensitized Cancer Cell Ablation

Abstract

Engineering π-conjugated molecules with donor(D)−acceptor(A) functional groups to regulate self-assembly behavior and fluorescence emission phenomena has remained captivating yet challenging to understand accurately their immense potential due to the complex molecular motion in the condensed state. Herein, two pairs of D−A-based orange (∼570 nm)/red (∼640 nm) emissive luminogens have been developed by varying the heteroatom in the donor functionality and the position of nitrogen atom in the cyano-pyridine acceptor. The molecular motion governed the regulation of emission properties during the transformation of the monomers to nanoaggregates and ultimately macrocrystals, depending on the surrounding molecular environment. An in-depth analysis of the single crystals of these molecules, grown in different solvent systems, reveals a pioneering concept of tuning the condensed-state emissive behavior correlated to molecular conformation and intermolecular interaction. Further, the molecular motion-induced luminescence variation was tweaked with external stimuli through a phase change matrix (PCM), enabling the development of a rewritable security ink for data encryption based on the thermochromic transition. Notably, the low ΔE_ST values facilitated excellent reactive oxygen species (ROS) generation, particularly following the type-I photodynamic therapy (PDT) process for effective image-directed phototheranostic killing of cancer cells. This concept thus provided vital leads for designing molecular motion-based conformation studies that trigger specific wavelength modulation, offering multidimensional applications as robust, rewritable thermochromic ink and permitting organelle-specific cellular imaging along with ROS-assisted photosensitized cancer cell ablation.