Effect of N-methyl and ethyl on phosphorescence of carbazole in cocrystals assembled by CI⋯π halogen bond, π-hole⋯π bond and other interactions using 1,4-diiodotetrafluorobenzene as donor

Two phosphorescent cocrystals were prepared by 1,4-diiodotetrafluorobenzene (1,4-DITFB) and N-methylcarbazole (cocrystal 1) and N-ethylcarbazole (cocrystal 2) based on CI⋯π halogen bond, π-hole (πh)⋯π bond and CH⋯π, CH⋯F hydrogen bond as well as F⋯F contacts, in which 1,4-DITFB molecule acts simultaneously as the cement to link luminescence molecules and the heavy atom perturber to enhance phosphorescence of emitters by spin–orbital coupling. The cocrystals were also well characterized by powder XRD, FT-IR, Raman, DSC and DTA analysis and also estimated the bonding energies by calculation. Different steric effects of N-substituted groups on the carbazole backbone leads to the different CI⋯π bonding stoichiometry and π-hole⋯π bonding modes and then lead to the phosphorescence spectra red- or blue-shift compared with carbazole-1,4-diiodotetrafluorobenzene cocrystal.