A cruciform electron donor-acceptor semiconductor with solid-state red emission: 1D/2D optical waveguides and highly sensitive/selective detection of H₂S gas

In this paper, a new cruciform donor-acceptor molecule 2,2'-((5,5'-(3,7- dicyano-2,6-bis(dihexylamino)benzo[1,2-b:4,5-b']difuran-4,8-diyl) bis(thiophene-5,2-diyl))bis (methanylylidene))dimalononitrile (BDFTM) is reported. The compound exhibits both remarkable solid-state red emission and p-type semiconducting behavior. The dual functions of BDFTM are ascribed to its unique crystal structure, in which there are no intermolecular face-to-face π-π interactions, but the molecules are associated by intermolecular CN...π and H-bonding interactions. Firstly, BDFTM exhibits aggregation-induced emission; that is, in solution, it is almost non-emissive but becomes significantly fluorescent after aggregation. The emission quantum yield and average lifetime are measured to be 0.16 and 2.02 ns, respectively. Crystalline microrods and microplates of BDFTM show typical optical waveguiding behaviors with a rather low optical loss coefficient. Moreover, microplates of BDFTM can function as planar optical microcavities which can confine the emitted photons by the reflection at the crystal edges. Thin films show an air-stable p-type semiconducting property with a hole mobility up to 0.0015 cm ²V^-1s^-1. Notably, an OFET with a thin film of BDFTM is successfully utilized for highly sensitive and selective detection of H₂S gas (down to ppb levels).