Abstract
Two-dimensional (2D) polyaniline (PANI) has been realized for the first time, to our knowledge, by direct solid-state reaction of organic single crystals. The 2D PANI framework consists of six nitrogen atoms that periodically surround a phenyl ring. Pristine 2D PANI (undoped) has electrical conductivity of 0.72 S/cm, which is 10
10
times higher than its linear analog (undoped, 6.28 × 10
−11
S/cm). When it is doped by hydrochloric acid (HCl), its conductivity jumps to almost 1,960 times (1.41 × 10
3
S/cm). Due to its highest conductivity among organic materials, we very strongly believe that this well-defined 2D PANI and its heterogeneity with C and N elements will open up a new research field of layered 2D materials beyond linear PANI and other organic/inorganic 2D materials.
The formation of 2D polyaniline (PANI) has attracted considerable interest due to its expected electronic and optoelectronic properties. Although PANI was discovered over 150 y ago, obtaining an atomically well-defined 2D PANI framework has been a longstanding challenge. Here, we describe the synthesis of 2D PANI via the direct pyrolysis of hexaaminobenzene trihydrochloride single crystals in solid state. The 2D PANI consists of three phenyl rings sharing six nitrogen atoms, and its structural unit has the empirical formula of C
3
N. The topological and electronic structures of the 2D PANI were revealed by scanning tunneling microscopy and scanning tunneling spectroscopy combined with a first-principle density functional theory calculation. The electronic properties of pristine 2D PANI films (undoped) showed ambipolar behaviors with a Dirac point of –37 V and an average conductivity of 0.72 S/cm. After doping with hydrochloric acid, the conductivity jumped to 1.41 × 10
3
S/cm, which is the highest value for doped PANI reported to date. Although the structure of 2D PANI is analogous to graphene, it contains uniformly distributed nitrogen atoms for multifunctionality; hence, we anticipate that 2D PANI has strong potential, from wet chemistry to device applications, beyond linear PANI and other 2D materials.