• 10.1021/ja064726s
  • Journal of the American Chemical Society
  • Volume 128
  • December 2006
  • pp 15940-15941

A Cyclic Triphenylamine Dimer for Organic Field-Effect Transistors with High Performance

Review of the novel materials for future organic electronics


The manuscript entitled ''A cyclic triphenylamine dimer for organic field-effect transistors with high performance'' is a nice piece of work. A new OFET based on triphenylamine units with a macrocyclic architect has been described with its potential use as high performance OFET devices. A macrocycle was synthesized by a pathway involving the Vilsmeier Haack di-formylation of triphenylamine followed by the McMurry coupling reaction under the dilute reaction conditions to get the macrocycle. Thus the Ruggli-Ziegler dilution principle is well applied to make a molecular electronics material. The cyclic structure leads to a significant reduction of the reorganizational energy. A closed ring and steric crowd in this macrocycle restricted the rotation of the phenyl groups which led to a typical column and layer-by-layer packing fashion resulting in an efficient hole transportation. Macrocycle formed highly crystalline layer-structure in thin films while, linear analogue formed amorphous films! Thus ring formation is a tool to tune the performance of a semiconductor. The hole mobility (µ) of macrocycle deposited at 22 °C was found to be 1.5 × 10 cm2 V-1 s-1, which was 100 times as high as that of linear analogue (2 × 10-4 cm2 V-1 s-1) under the same condition.  Highest on/off ratios of the order of 10 power7 was observed for macrocycle. The theoretical room temperature hole-diffusion mobility was obtained to be 2.1 × 10-2 cm2 V-1 s-1 for macrocycle and 1.9 × 10-3 cm2 V-1 s-1 for linear analogue. Both matched well with the experimental results. I carried out the similar reactions in my lab and found that they are reproducible. The selective diformylation of the triphenylamine was achieved by using the typical formylation conditions as used in the reference1 and its sub-reference2 in the original paper. All the three products, the mono-, di-, and triformylated were possible, but the selectivity was achieved by tuning the reaction conditions like temperature, time, equivalents etc. The yield of the final step ie. the McMurry coupling was little low (9%). I performed the similar reactions with diphenylamine. The product I got was instead, the N-formylated because of the nucleophilic nature of N-atom. I tried the formylation of the N-formylated product again, but the attempt failed, possibly due to the deactivation of the p-positions of the phenyl rings by the N-formyl group. However currently I am modifying the N-formyl derivatives to incorporate them in to my work. Some dialdehydes are expected which may give the last products with increased yiels (currently one of the product has been got in 22% yield possibly due to a more favourable structure of the dialdehyde for the reductive McMurry couping. The reagents of the McMurry coupling reaction can be changed to Titanium tetrachloride (11 eq), Zn dust (20 eq, activated) and Pyridine (20 eq, dried). The Zn-Cu couple can also be tried, to increase the %age yield and thus minimising the loss of reagents, time, labour etc. Overall this is a nice study. Typical reaction skills have been gathered to develop a high performance material for organic electronics.

(1) Wang, X.; Wang, D.; Zhou, G.; Yu, W.; Zhou, Y.; Fang, Q.; Jiang, M. J. Mater. Chem. 2001, 11, 1600.

(2) Mallegol, T.; Gmouh, S.; Meziane, M. A. A.; Blanchard-Desce, M.; Mongin; O. Synthesis 2005, 11, 1771.

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