Photophysical properties of octupolar triazatruxene-based chromophores

The photophysical properties of three octupolar chromophores containing planar triazatruxene (TAT) as the central electron donor with different electron-withdrawing groups in the tribranched arrangement have been systematically investigated by means of steady state and transient spectroscopy. The multidimensional intramolecular charge transfer (ICT) properties of these tribranched chromophores related to the observed two-photon absorption (TPA) properties are explored by estimating the TPA essential factors (M_ge and Δμ_ge). Besides the large Stokes shift between steady state absorption and fluorescence spectra in different polar solvents, photoinduced ICT was further demonstrated by quantum-chemical calculations and transient absorption measurements. Both quantum calculations and spectral experiments show that a multidimensional ICT occurs from the electron-rich core to the electron-deficient periphery of these TAT derivatives. The results of solvation effects and the dynamics of the excited states show that the excited states of these three chromophores tend to exhibit an excitation localization on one of the dipolar branches, which is beneficial to achieve large M_ge and Δμ_ge, thus leading to enhanced TPA properties.