Aromaticity in Polyacenes and Their Structural Analogues

The successful synthesis of different polyacenes including theoretical assessment on the stability of larger acenes are discussed. The existence of favorable aromaticity criterion in polyacenes is understood in terms of different aromaticity indicators like nucleus independent chemical shift (NICS), harmonic oscillator model of aromaticity (HOMA), bond resonance energy (BRE). Clar's Π- sextet rule is also very much effective in explaining their aromaticity. By virtue of low HOMO-LUMO gap, the probable application of polyacenes in the field of organic electronics is also highlighted. The polyacene analogues of inorganic ring compounds, viz., BN-acenes, CN-acenes, BO-acenes, BS-acenes, AlN-acenes and of alkali ring compounds, viz., Na-acenes and K-acenes also have polyacene-like aromaticity although in few cases the origin of aromaticity and qualitative nature of aromaticity differ significantly.