posted on 2022-01-10, 21:17authored bySirui Yang, Chen Cao, Jiayu Li, Ziqi Deng, Shaofei Ni, Jing-Xin Jian, Qing-Xiao Tong, Li Dang, Ming-De Li
Charge
transfer plays an important role in photophysical and photochemical
reactions. However, the factors affecting the excited charge-transfer
state are unclear. Here, two donor−π–acceptor
dyads with an excellent blue fluorescence quantum yield are designed
by integrating 1,2-diphenylphenanthroimidazole (PPI) as an electron
donor and 1,2,4-triazolopyridine (TP) as an electron acceptor through
phenyl (P) bridges. In the solvents dichloromethane (DCM) and dimethyl
formamide (DMF), the dynamics of intramolecular charge transfer (ICT)
of the two dyads (TP-P-PPI and TP-P-P-PPI) is located at the Marcus
normal region, while the dynamics of charge recombination (CR) is
situated at the Marcus inverted region. Therefore, TP-P-P-PPI with
a long π-chain exhibits a longer lifetime of ICT but a shorter
lifetime of CR than TP-P-PPI does with a short π-chain. In contrast,
when the two dyads are spin-coated into a film, the dynamics of ICT
and CR processes of the two dyads are restored to be positively correlated
with the π-chain length because of the inhibition of intramolecular
torsion between PPI and TP in the excited state of the film. This
work demonstrates a specific approach via the molecular torsion to
tune the dynamics of the ICT and CR among donor−π–acceptor
systems.