Ultrafast response of Diketo-Pyrrolo-Pyrrole dyes with large two-photon absorption enhancement as well as AIE property

To study the effect of terminal groups substituent on the two-photon absorption (TPA) properties of [Formula: see text]-[Formula: see text]-[Formula: see text]-[Formula: see text]-[Formula: see text] structural dyes with diketo-pyrrolo-pyrrole (DPP) as central electron acceptor group, linear/transient absorption spectroscopy, one/two-photon fluorescence spectra, open-aperture [Formula: see text]-scan, and excited states quantum chemical calculations have been performed to systematically study the intermediate product electron acceptor J0 as well as three [Formula: see text]-[Formula: see text]-[Formula: see text]-[Formula: see text]-[Formula: see text] structural dyes using benzene, triphenylamine and 2,3-methoxy-triphenylamine as terminal electron donors, named as J1, J2, and J3, respectively. The intermediate product electron acceptor itself exhibits a relatively large TPA response, which indicates the DPP group has a large conjugated system. J2, with strong electron-donating ability groups triphenylamine as terminal groups, shows a large TPA cross-section of 534[Formula: see text]GM, which is approximately 10 times larger than that of J1 with weak electron pushing/pulling abilities groups benzene as terminal groups (51[Formula: see text]GM). The result indicates that the electron-donating abilities of terminal groups do play a key role in TPA response. Furthermore, methoxy substituent on the terminal triphenylamine groups can further effectively increase the TPA response, J3exhibits a 15-fold enhancement compared with that of J1. Transient absorption spectra and quantum chemical calculation results are well accorded with the experimental results. Terminal substituents with strong electron donor groups are beneficial for the formation of intramolecular charge transfer (ICT) process. Besides, methoxy substituent in the terminal of triphenylamine groups can further enhance the degree of ICT and induce AIE characteristics in the molecule.