| In this work, we used femtosecond time-resolved transientabsorption spectroscopy technology in experiment combined withtime-dependent density functional theory (TDDFT) method in theory andinvestigated the effect of hydrogen bond on excited state charge transfermechanism of coumarin500(C500). We measured steady-stateabsorption spectrum, fluorescence spectrum and transient absorptionspectrum of C500in1,4-dioxane (Diox) and methanol (MeOH) solvents.Our femtosecond transient absorption experiment on C500shows that inDiox, there exists a single exponential component with a time constant ofτ1~1.4ps, however in MeOH two exponential components withlifetimes of τ1~0.5ps and τ2~8.0ps are observed. We calculatedgeometric structures in ground state and excited state, electronicexcitation energies and frontier molecular orbitals (FMOS) ofhydrogen-bonded complexes C500–Diox and C500–(MeOH)3,respectively. It shows that in Diox, C500exists intramolecular chargetransfer (ICT) state, however in MeOH ICT state and twisted intramolecular charge transfer (TICT) state are found. They show that therapid decay time could be due to the process of ICT and theconversionfrom ICT state to TICT state could be responsible for the slow decay time.The different excited state charge transfer mechanisms are fundamentaldifference between C500in Diox and MeOH revealing that C500hasunusual properties in different hydrogen bonding solvents. |
