While many conjugated organic materials have been extensively studied for their unique optical and electrical properties, fused heterocyclic compounds, particularly ladder oligomers, have received comparatively less attention. Research exploring how the shape, nature of heteroatoms, and their relative positions influence the structural, spectroscopic, photophysical, and electrochemical properties of these materials remains limited. This study aims to investigate these factors and their impact on the properties of fused heterocyclic ladder oligomers. We conducted a series of synthesis, photophysical, electrochemical, single-crystal structural studies, and density functional theory (DFT) calculations on a range of structurally related ladder oligomers. Our findings suggest that the properties of these materials can be fine-tuned to meet specific application requirements. We also have successfully synthesized tow appreciably water-soluble half and full ladder molecules functionalized with carboxylic acid derivatives for use in optical and electrochemical biosensors, demonstrating significant fluorescence and reversible redox properties. Cyclic Voltammetry (CV) studies revealed distinct redox behavior across the series of compounds. For instance, 6-chloro-9-nitro-5H-benzo[a]phenoxazin-5-one exhibited an oxidation potential of 0.059 V, while (benzo[a]benzo[5,6][1,4]thiazino[3,2-c]phenothiazine displayed multiple reduction potentials of -0.039 V, -0.215 V, and -0.332 V, indicating its capability for multi-step electron acceptance. These multi-step reduction processes underscore their applicability for electron storage and transfer in organic photovoltaics and various optical and electrochemical biosensors. In addition, Differential Scanning Calorimetry (DSC) provided critical insights into the thermal stability of these compounds with melting points ranging from 150 to 340°C. These elevated melting points reflect enhanced thermal durability, rendering the compounds suitable for various electronic and photovoltaic applications, where reliable performance and improved charge carrier mobility are essential. Finally, the introduction of amino and carboxylic functional groups allows for the attachment of numerous biologically significant molecules, facilitating the preparation of corresponding polyamides and polyesters. Five molecules are included in this study: 6,9-dichloro-5H-benzo[a]phenoxazin-5-one; 6-chloro-10-nitro-5H-benzo[a]phenoxazin-5-one; 13-chlorobenzo[a]benzo[5,6][1,4]oxazino[3,2-c]phenothiazine; 13-nitrobenzo[a]benzo[5,6][1,4]oxazino[3,2-c]phenothiazine; benzo[a]benzo[5,6][1,4]oxazino[3,2-c]phenothiazine-13-carboxylic acid and 6-chloro-9-(hydroxy-l2-methoxy)-5H-benzo[a]phenoxazin-5-one. Each of these compounds exhibits a high degree of conjugation, and planarity which are responsible for their distinct optical and electronic properties. 

2025

May 2025