In this manuscript, the single crystalline wires were grown from π-extended porphyrin derivatives TTPH2 1 and TTPZn 2, and their unique electronic properties in OFET devices along with single-crystal structures. 1 was readily obtained in relatively high yield (21%) by using a typical porphyrin condensation reaction between 4-((5-hexylthiophene-2-yl)ethynyl)benzaldehyde and pyrrole in propionic acid. 2 was further obtained by metallation of TTPH2 1 with Zn(OAc)2 in 78% yield. A relatively low band gap is found in metalloporphyrin TTPZn. The experimental results indicate that the devices fabricated from single crystal of 1 and 2 display excellent OFET performances. The carrier mobilities are 6.2 × 10-2 cm2 V-1 s-1 for 1 and 0.32 cm2 V-1 s-1 for 2 with a high on/off current ratio of >10 power4. These values were among the best for porphyrin-based OFET devices. Since the mobility is highly dependent on the stacking distance between building blocks in the solid state, the single-crystal device of TTPZn 2, which has the shorter packing distance between layers, shows much better device performance than that of TTPH2 1 evidenced by single-crystal X-ray structure analysis. The smaller bandgap (Eg) of TTPZn 2 (Eg = 1.80 eV) compared with TTPH2 1 (Eg = 1.93 eV) further supports that the Zn metallation could make the porphyrin system behave as a better OFET device. For comparison, the performances of the corresponding thin film devices prepared by spin coating the solutions of 1 and 2 in chloroform was studied too. Interestingly, the device performances drop down dramatically and the observed carrier mobilities are in the range of about 2.3 × 10-4 – 3.5 × 10-4 cm2 V-1 s-1 These dramatic drops in mobility are presumably due to a decrease of their molecular order upon aggregations of porphyrins during the film formation. However, the UV-Vis. absorption and photoluminescence (PL) spectra in solution and film forms of 1 and 2 show that 2 generates densely packed aggregates in the solid state. The absorption spectra reveal slight red shifts of around 5–8 nm upon the film formation in both 1 and 2 that indicate ineffective intermolecular interactions. Thus due to low crystallinity, their film device performances drop dramatically. Thus with a high mobility value, these new porphyrin derivatives have demonstrated that porphyrin building blocks have strong potential for use in electronic and optoelectronic applications. The dieldctric modification or the thermal annealing of the thin film devices can also be checked to increase the device performance. The size and weight of the single crystals can also be varied especially reduced which may lead to development of a corelation between the size of the crystals and the performance or may lead to a better performance in small sized crystals. For reference please consult the reference [1*]
[1*] Li, R.; Li, H.; Song, Y.; Tang, Q.; Liu, Y.; Xu, W.; Hu, W.; Zhu, D. Adv. Mater. 2009, 21, 1605–1608.
Its a nice study otherwise.