Effect of Carbazolyl Groups on Photophysical Properties of Cyanuric Chloride

Long-lived room temperature organic phosphorescence is
highly useful in biological imaging, electroluminescent devices, information
security, and security protection on account of its unique photophysical
process and long-lived luminescence. In recent years, pure organic
phosphorescent materials that do not contain rare precious metals
have received increasing attention. Carbazole and its derivatives
have been used to develop room temperature organic phosphorescent
materials. However, the effect of carbazolyl groups on the photophysical
properties of pure organic phosphors has rarely been reported. In
this work, three cyanuric chloride phosphors (CzDCIT, BiCzDT, and
TCzT) modified with different numbers of carbazolyl groups were synthesized.
Several characterization techniques were employed to reveal distinct
crystal forms of CzDCIT, BiCzDT, and TCzT. The single crystal diffraction
of CzDCIT and BiCzDT showed not only different crystal packing modes,
but also the formation of internal H-aggregation.
These three phosphor powders exhibited dual emissions of blue fluorescence
and yellow phosphorescence at room temperature, with luminescence
lifetimes of 0.16–0.34 s. Theoretical calculations indicated
that different numbers of effective intersystem crossing channels
between CzDCIT, BiCzDT, or TCzT were responsible for the luminescence
lifetimes. After doping the phosphors into the polymer matrix, they
exhibited good persistent phosphorescence and high recoverability
in multiple compression-grinding cycles.