Conjugated Iminodibenzyl Dyes Incorporating Phenolic Hydroxyl Group and Strong Electron Donating or Accepting Groups for Facilitating ESIPT and Proton Transfer in Six- or Seven-Membered Cycles.

In this study, a range of conjugated iminodibenzyl derivatives D1-D6 including phenolic group and strong electro donating/accepting groups (N,N-diethylamino/nitro groups) were prepared as the target dyes, which could process internal proton transfer in excited state via six-/seven membered ring transition state (TS). Furthermore, reference iminodibenzyl dyes D7-D12, devoid of the phenolic segment, were synthesized for comparative analysis of their absorption and emission spectral properties. The internal H-bond of the target dyes was analyzed by the H-NMR spectroscopy and ultraviolet/visible absorption spectroscopy. As compared with the reference dyes, the steady and transient fluorescence measurements suggest that the target dyes D1-D3 CAN undergo excited state intramolecular proton transfer occurring through a six membered ring TS in various organic solvents. However, the target dyes D4-D6 CAN NOT process internal proton transfer in the excited state through a seven membered ring TS. Furthermore, the strong electron donating/accepting substituted groups show an effect on internal hydrogen bond in the target dyes, and thus they display influence on intramolecular proton transfer in the excited state of the target dyes D1-D3. The molecular modeling of the target dyes was further performed to reveal ESIPT through a six membered ring TS of the target dyes D1-D3 can occur, but ESIPT through a seven membered ring TS of the target dyes D4-D6 may not happen.