A leaning amine-ketone dyad with a nonconjugated linker: solvatofluorochromism and dual fluorescence associated with intramolecular charge transfer

• Published in: Photochemical & photobiological sciences 2018, Vol.17 (9), p.1157-1168
• Main Authors: Kuramoto, Yutaro, Nakagiri, Takanobu, Matsui, Yasunori, Ohta, Eisuke, Ogaki, Takuya, Ikeda, Hiroshi
• Format: Article
• Language: English
• Subjects: Biochemistry; Biomaterials; Charge transfer; Chemistry; Conjugation; Dipole moments; Electron transfer; Electrons; Fluorescence; Physical Chemistry; Plant Sciences; Saturated hydrocarbons; Solvents
• ISSN: 1474-905X; 1474-9092
• DOI: 10.1039/c7pp00453b

Dyad 4 , comprising a triphenylamine (TPA) electron donor and 1,4-pentadien-3-one (pentadienone) electron acceptor tethered by a nonconjugated linker, displays solvatofluorochromism (SFC) and dual fluorescence associated with intramolecular charge transfer (ICT) in the excited state. While the fluorescence arises from a locally excited state of 4 (LE- 4* ) in saturated hydrocarbon solvents, the fluorescence from the ICT state of 4 (ICT- 4* ) occurs in aprotic solvents. ICT- 4* has a much greater dipole moment than its corresponding ground state. The results of theoretical calculations suggest that the conversion of LE- 4* to ICT- 4* involves a unique structural change like a leaning of the pentadienone moiety. Two factors are responsible for the significant SFC displayed by 4 , the first being the high electron-donating and -accepting abilities of the respective locally excited TPA and pentadienone moieties in LE- 4* and the other being a rigid ethano bridge that links the two moieties in ICT- 4* . The former property facilitates photoinduced electron-transfer (PET) and the latter prevents full single electron transfer (SET) by prohibiting direct π-conjugation and the spatial approach of the two dyad components. Consequently, these electronic and geometrical features lead to SFC arising from a large dipole moment change caused by ICT and partial intramolecular SET. A amine-ketone dyad with a nonconjugated linker displays solvatofluorochromism and dual fluorescence due to intramolecular charge transfer in the excited state accompanied by a change of the molecular geometry like leaning.