Unveiling the Photophysical Properties of Indole-Containing Boron Complexes: Exploring Intramolecular Charge Transfer Character, Tunable Emission, and Large Stokes Shifts.

Embedding boron into indole scaffolds offers promising potential for a diverse range of applications, since both indole and boron-containing compounds possess remarkable and adjustable chemical, photochemical, and photophysical properties with effortless modifications. In the present study, we showed synthesis and characterization of indolyl-7-imines-based NN boron complexes. These indole boron platforms were extensively characterized using steady-state absorption, fluorescence, and ultrafast transient spectroscopy for their photophysical properties and excited-state dynamics in various solvents. More importantly, our targeted compounds exhibited intramolecular charge transfer (ICT) phenomena, resulting in substantial Stokes shifts and tunable emissions. Theoretical results reported that large Stokes shifts mainly result from the spatial arrangement of HOMO and LUMO energies, with reduced oscillator strengths during the emission process indicating enhanced charge transfer (CT). Notably, tailoring the peripheral phenyl groups allowed the precise control of CT contribution, demonstrating the possibility of manipulating the photophysical properties of indolyl-imine-based NN boron complexes. These findings indicate that this system is one of the most adaptable and tunable among the reported NN boron complexes-based molecular systems. The present study critically underscores the potential of NN boron complexes as a promising building block for applications requiring large Stokes shifts, such as biomedical applications or organic light-emitting diodes.