Morphological Modulation of an Aggregation-Induced Emissive Chromophore for Enhanced Semiconducting and Photoswitching Performance of an Amino Acid-Containing Naphthalene Monoimide

The development of high-performance optoelectronic materials through morphology tuning induced by acid vapors remains a significant challenge. In this study, we present the synthesis and characterization of a novel molecule, PTHN, which integrates pyrene-butyric-acid-appended histidine with a naphthalene monoimide core. The PTHN molecule exhibits aggregation-induced emission in a DMSO-H₂O solvent mixture and displays bright yellow fluorescence in the solid state under UV illumination (λ = 365 nm). Notably, the solid-state emission of PTHN is quenched upon exposure to various acid vapors including trifluoroacetic acid (TFA), HNO₃, HCl, and H₂SO₄. The quenching efficiencies and corresponding limits of detection were determined to be 1.83 ppm (TFA), 0.32 (HNO₃), 0.62 (HCl), and 5.0 ppb (H₂SO₄), respectively. In a DMSO/H₂O (3:97, v/v) mixture, PTHN aggregates into vesicular structures. Upon exposure to acid vapors, however, a distinct morphological transformation occurs, with the vesicles converting into fibrous networks. Dynamic light scattering measurements reveal a significant increase in the hydrodynamic volume and positive zeta potential, suggesting the incorporation of positive charges. The optoelectronic properties of PTHN, including electrical conductivity and photoswitching behavior, were systematically investigated before and after acid vapor treatment. Current-voltage (<i>I</i>-<i>V</i>) measurements show a drastic increase in current from 18 nA to 35 μA at +5 V, representing a 1944-fold enhancement. The system also demonstrated a maximum photocurrent gain of 6.28 in the presence of TFA vapor. This remarkable enhancement in conductivity and photoresponse is attributed to the formation of interconnected fibrous networks upon acid exposure. These findings highlight the potential of PTHN as a promising material for acid vapor sensing and optoelectronic applications, offering high sensitivity, morphological responsiveness, and efficient photocurrent conversion.