Resonant two-photon ionization of aromatic hydrocarbons included in cyclodextrins

• The transient absorption of straight-chain aromatic hydrocarbons in the presence of cyclodextrins in water/acetonitrile (9:1 v/v) was observed using flash photolysis.
• Photoionization of straight-chain aromatic hydrocarbons occurred from S0 → S1 → Sn transition by two photons.
• This work helps to establish the relationship between the structure and photoionization behavior of the inclusion complexes formed between straight-chain aromatic hydrocarbons and cyclodextrins.
• The straight-chain aromatic hydrocarbons with three benzene rings exhibited the highest TPI efficiency of those investigated in the presence of various cyclodextrins.

The photodynamics of host–guest interactions may be useful in applications such as sensing and molecular recognition. However, the photoionization behavior of straight-chain aromatic hydrocarbons (SCAHs), including biphenyl (1), p-terphenyl (2), p-quaterphenyl (3), m-terphenyl (4) and o-terphenyl (5), in host–guest complexes is not well understood. Here, we examine the photocharacteristics of inclusion complexes formed between 1–5 and various cyclodextrins (CDs) in water/acetonitrile (9:1 v/v) by transient absorption measurements using laser flash photolysis to determine the influence of structure on the photoionization properties of inclusion complexes. Resonant two-photon ionization of 1–5 included in the CDs occurred following irradiation with a 266-nm laser pulse. The ionization quantum yields (Φion) of the inclusion complexes were influenced by fluorescence lifetime, the stabilization energy arising from solvation, which was affected by the area of the SCAH protruding from the cavity of the CD, and excimer formation. 2 exhibited the highest Φion of the SCAHs by inhibition of excimer formation and its structure was relatively susceptible to the stabilization energy resulting from solvation. This work helps to establish the relationship between the structure and photoionization behavior of the inclusion complexes formed between SCAHs and CDs.

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