Photophysical and morphological properties of Langmuir–Blodgett films of benzothiadiazole derivatives

Organic semiconductors with extended π-conjugate systems have been extensively investigated to be implemented and improve optoelectronic devices. It is well known that benzothiadiazole (BTD) derivatives have interesting semiconductor properties that make them suitable materials for optoelectronic applications. In this work, the photophysical properties of 4 BTD with triphenylmethyl and triphenylsilyl derivatives in solution exhibited larger Stokes shifts, which can be attributed to the length and conjugation of these molecules. On the other hand, the quantum yields observed for these systems were larger than 0.5. In addition, the formation of Langmuir monolayers at the air–water interface with isotherms showing high collapse pressures around 60 mN/m, and stable compression–decompression cycles (hysteresis) were obtained. Langmuir–Blodgett films onto glass substrates were formed with these compounds by using the Z-type deposit with transfer ratios close to 1. In addition, high-fluorescence emission responses were observed for the BTD derivatives that did not contain silicon in their structure. Also, using scanning electron and atomic force microscopies, regular surface morphologies were observed for the silicon-less compounds, but higher roughnesses and fiber-like structures for the other films. From these results, these BTD films can be potential candidates to be employed in photoelectronic applications.