Expounding the Relationship between Molecular Conformation and Room-Temperature Phosphorescence Property by Deviation Angle

Room-temperature phosphorescence
(RTP) emitters with ultralong
lifetimes are attracting more and more attention for their wide applications.
However, it is still a big challenge to achieve persistent organic
afterglow because of the undefined relationship between molecular
structures and RTP effect. Herein, diphenylamine (DPA) as a commonly
used building block is selected as the molecular skeleton. Through
incorporation of various alkyl moieties by ortho-substitution
in different numbers and positions, RTP lifetimes can increase from
129 to 661 ms with the subtle adjustment of molecular conformations.
It is summarized that the deviation angle (θ) of phenyl units
in the DPA skeleton from the ideal p-π conjugated
plane can act as the key parameter determining RTP lifetime, and the
larger the θ values, the longer the RTP lifetimes. Furthermore,
this result has been successfully applied as the universal principle
to explain the RTP properties of various organic luminogens with DPA
blocks and similar structures.