Molecular conformation dependence of phosphorescence lifetime in organic aggregates

Organic bulk crystal with room-temperature phosphorescence (RTP) is normally fabricated into nanoparticles (NPs) for biological applications, accompanying with inevitable change in RTP lifetime and molecular conformation. By using molecular dynamics and quantum chemistry methods, the difluoroboron beta-diketonate (BF2bdk) compound (Br-NpCzBF2) was explored to uncover the molecular conformation-dependent RTP from crystal to NPs. We proposed that from crystal to amorphous aggregates, the distorted BF2bdk group caused by the weakened intermolecular B-FMIDLINE HORIZONTAL ELLIPSISH-C hydrogen bonds convert the T1 from hybridized local and charge transfer to locally excited states. Such change strengthens the vibronic coupling effect on the C--C stretching vibration, and enormously accelerates the nonradiative decay rate of T1 -> S0 by 1-2 orders of magnitude. Consequently, the RTP lifetime is shortened from 566 mu s in crystal to about 10 mu s in amorphous aggregates, which is consistent with the experiments. This work provides new insight into the RTP mechanism and opens a novel design avenue for designing organic RTP materials in biological fields.

Automated summary

This study investigated the impact of molecular conformation on RTP in the BF2bdk compound, revealing a significant decrease in RTP lifetime from crystal to amorphous aggregates. This offers new insights into the design of organic RTP materials in biological applications.