Dark DC conductivity and spectroscopy of clean and gas doped thin films of organic semiconductors

The dark DC conductivity of thin films of phthalocyanine (I), meso-tetra(p-methylphenyl)porphin (II), meso-tetraphenylporphin (III), hemiporphyrazine (IV), dihydrodibenzo b,i]1,4,8,11] tetra-azacyclotetradecine (V) and three derivatives of V have been studied in vacuo and in the presence of a wide range of gases. The only gases to produce marked increases in the conductivity were electron acceptors; however, IV was unaffected even by these. The interactions of I, II, III and V and its derivatives with $\text{NO}{}_2\text{N}{}_2\text{O}{}_4$ (NOX) were of particular interest and were studied by conductivity measurements, UV/VIS and IR transmission spectroscopy and IR reflectance spectroscopy. The material most sensitive to NOX and other electron acceptors was I; however, V has a favourable combination of sensitivity coupled with reversibility at room temperature. The Interactions of NOX with I, II and HI are complex, and there is spectroscopic evidence for the generation of NO₂ and the organic radical cations.