One-step synthesis of a new photoelectron-accepting, n-dopable oligo(pyrazole)

• A facile synthesis of a new electron-accepting tetramer is described.
• The tetramer is based on an inexpensive, readily available pyrazole derivative.
• The tetramer was incorporated into a prototype photodiode, which demonstrated a very high detectivity (2.7 × 1012 Jones).

A new photoelectron-accepting, n-dopable organic oligomer has been synthesized in a single step. It is a fluorescent tetramer formed from a substituted aminopyrazole, 3-amino-1H-pyrazole-4-carbonitrile, which has a low cost (about two USD per gram). Its chemical structure was verified using FTIR, mass spectrometry, and 1H/13C NMR. When used as an electron acceptor in an ITO-supported photocell containing a PEDOT-PSS hole transporting layer, the tetramer can support photocurrents of as high as 1.40 × 10−4 A at 0 V bias, and 7.20 × 10−3 A above baseline at 1.0 V bias. The cell, having a fabrication method that is not yet optimized, showed a photodiode responsivity of as high as 0.48 A/W, and a sensitivity of as high as 6.0 × 10−4 Sm/W. Most importantly, it also demonstrated a detectivity of as high as 2.7 × 1012 Jones, which is comparable to state-of-the-art inorganic photodiodes. The tetramer may represent a new, very inexpensive class of conducting organics useful in polymer-based photodiodes and solar cells.