Understanding
how the conformational change of conjugated molecules
with acceptor–donor–acceptor (A–D–A) architecture
affects their physical and optoelectronic properties is critical for
determining their ultimate performance in organic electronic devices.
Here, we utilized femtosecond transient absorption, time-resolved
upconversion photoluminescence spectroscopy, and tunable femtosecond-stimulated
Raman spectroscopy, aided by quantum chemical calculations, to systematically
investigate the excited state structural dynamics of the intramolecular
charge transfer of the tetramethoxy anthracene-based fluorophore 2,3,6,7-tetramethoxy
9,10-dibenzaldehydeanthracene (AnDA) and its derivative 2,3,6,7-tetramethoxy
9,10-diphenylanthracene (TMDPAn) in chloroform. In the AnDA molecule,
the tetramethoxy anthracene and benzaldehyde moieties exhibit a strong
ability to donate and withdraw electrons. Upon photoexcitation, AnDA
shows intriguing ultrafast fluorescence switch-on and red shift dynamics
on charge transfer states, and the temporal evolution of AnDA recorded
by ultrafast spectroscopy reveals a dynamic picture of two-step intramolecular
charge transfer assisted by ultrafast conformational changes and solvation
processes. Removing the aldehyde group from TMDPAn significantly decreases
the electron pulling capacity of the phenyl unit and disables charge
transfer characteristics.