Colorimetric Detection of Naphthalene Enabled by Intra- to Intermolecular Charge Transfer Interplay Induced by π-hole···π Interactions of a TPA-Attached Pyrazinacene

A new Donor-Acceptor type pyrazinacene derivative (1) featuring strong ICT was synthesized by linking electron-donating triphenylamine (TPA) and electron-accepting CN groups via a pyrazinacene core. The compound exhibits a dramatic color change from greenish blue to red-violet upon selective recognition of naphthalene (3) to form a 1:1 co-crystal (1•3). This color change is induced by intermolecular CT between pyrazinacene and naphthalene's aromatic moieties, driven by π-hole···π interactions. Crystal structure analysis and DFT calculations confirm that the molecular recognition process is facilitated by the unique π-hole···π interactions, leading to a reversible color switching mechanism. The findings offer new insights into selective molecular recognition and ICT-CT interplay in nonporous adaptive crystals.