Marilyn Daisy Milton

Solid-state emissive novel phenothiazine-indanone chalcones displaying reversible mechanofluorochromism, sensing of TFA and hydrazine, and anti-counterfeiting applications are reported.

Engineering transformable electronic features in two-terminal molecular junctions is of significant interest for advancing molecular-scale electronics. We demonstrate external stimuli (acid vapor)-responsive enhanced electrical current rectification (so called diode) in phenothiazine-based (R1) vertically stacked molecular junctions (MJs) with a configuration of p⁺-Si/R1_{58 nm}/ITO. The fabricated junctions exhibit nearly 530% enhancement in the electrical current rectification ratio (RR) in response to acid-vapor exposure for 60 seconds. The electronic functions of the devices can be partially set back using triethylamine (a weak base) vapor. Exposure to acid vapor forms cation radicals, (R1˙⁺)H⁺, that bring the lowest unoccupied molecular orbital (LUMO) closer to the Fermi level (E_F) of the ITO electrode in forward bias. In contrast, alignment of the highest occupied molecular orbital (HOMO) is not favorable under reverse bias conditions, which causes the emergence of the rectification ratio in the acid-exposed MJs. Electrical impedance spectra reveal a high charge transfer resistance (R_ct) of about 6 MΩ in pristine MJs, behaving like a resistor. However, the acid vapor facilitates an enhanced current flow at the forward bias compared to that at the reverse bias, mimicking diode functionality. The molecular junctions scrutinized for alternating current (AC) to direct current (DC) conversion using a function generator exhibit optimal diode performance at 500 Hz. Our findings demonstrate a method for high-yield device fabrication (∼86% working devices) that can be utilized for acid- and base-vapor-facilitated transformable electronic functions mimicking traditional electronics.

In this work, we designed and synthesized D‐A type tripodal phenothiazine derivatives to examine the influence of different functional groups on the photophysical properties and response to external stimuli. The compounds show emission in both solution and solid‐state. Intramolecular charge transfer (ICT) characteristics are evidenced by the fluorescence studies revealing positive solvatochromism in compounds. The compounds are highly thermally stable with low optical band gaps (2.1–2.55 eV). Compounds 3a‐3c displayed excellent aggregation‐induced emission enhancement (AIEE) phenomena in CH₃CN/DMSO and water mixtures. Compound 3e could detect moisture in three solvents, namely THF, CH₃CN, and DMSO, with the lowest detection limit of 0.018% in DMSO. The compounds show reversible acidochromism in solution and solid‐state, where compound 3e containing pyridyl shows the lowest detection limit for TFA of 0.59 ppm among others. The ‘ON‐OFF‐ON’ response to TFA/TEA stimulation has been utilized for the construction of the truth table and the outcome corresponds to the IMPLICATION logic gate. The sensitive response of compound 3e to amine vapors has been utilized for monitoring food spoilage. The compounds also show mechanofluorochromism, and the phase transformation was analyzed by powder X‐ray diffraction studies. These compounds are potential candidates for multi‐level anti‐counterfeiting applications and latent fingerprint sensing.Acidochromism; Aggregation‐induced emission enhancement (AIEE); Anti‐counterfeiting; IMPLICATION logic gate; Mechanofluorochromism

This work presents the design and synthesis of pyridopyrazine-based tripodal push–pull mol that show dual-state emission, and act as dual chemosensors for TFA and Hg²⁺ ions, and fluorescent thermometers.