Host-guest Interaction Induced Room-Temperature Phosphorescence Enhancement of Organic Dyes: A Computational Study
To achieve effective regulation of organic room temperature phosphorescence (RTP) in supramolecular systems, elucidation of host-guest interactions in RTP is of vital importance. Herein, we took two organic dyes (PYCl and PYBr) and their four host-guest complexes with CB[6] and CB[7] as examples and explored the mechanism of host-guest interaction induced RTP enhancement using quantum mechanics and molecular mechanics approach. For two organic dyes, we found that the better RTP performance of PYBr than PYCl is ascribed to the intersystem crossing (ISC) augmentation induced by heavy atom effect . B inding to CB[6] through host-guest interactions can simultaneously accelerate radiative decay process through increasing transition dipole moment of T 1 →S 0 (𝜇 T 1 →S 0 ), block nonradiative decay process, as well as promote ISC process, eventually leading to a remarkably boosted RTP. Upon complexation, the conversion of S 1 from 1 (n, π*) to 1 (π, π*) is key to 𝜇 T 1 →S 0 enhancement, the reduced reorganization energies reflect the suppression of nonradiative decay process by restricting the rotation of rings A and B in organic dyes. In addition, the promoted ISC process is due to the activation of more ISC channels between S 1 and high-lying triplet states with large spin orbital coupling constants and small energy gap. The case of CB[7]-type complexes is much different, because of too large cavity size of CB[7] for encapsulation. This work proposed the mechanism of host-guest interaction induced RTP enhancement of organic dyes, thus laying a solid foundation for the rational design of advanced RTP materials based on supramolecular assemblies.