Excited‐State THz Vibrations in Aggregates of Pt^II Complexes Contribute to the Enhancement of Near‐Infrared Emission Efficiencies**

Abstract

The exploration of deactivation mechanisms for near-infrared(NIR)-emissive organic molecules has been a key issue in chemistry, materials science and molecular biology. In this study, based on transient absorption spectroscopy and transient grating photoluminescence spectroscopy, we demonstrate that the aggregated Pt II complex 4H (efficient NIR emitter) exhibits collective out-of-plane motions with a frequency of 32 cm À 1 (0.96 THz) in the excited states. Importantly, similar THz characteristics were also observed in analogous Pt II complexes with prominent NIR emission efficiency. The conservation of THz motions enables excited-state deactivation to proceed along low-frequency vibrational coordinates, contributing to the suppression of nonradiative decay and remarkable NIR emission. These novel results highlight the significance of excited-state vibrations in nonradiative processes, which serve as a benchmark for improving device performance.

Ultrafast photophysics of an orange–red thermally activated delayed fluorescence emitter: the role of external structural restraint

“…The energy gap law (eqn (5)) clearly describes how promoting vibrational modes affect k S NR through their vibrational frequency ( ω M ) and reorganization energy ( λ M ), while promoting modes are vibrational modes that are considerably involved in the EVC of the S 1 state through a pronounced Huang-Rhys (HR) factor ( S k ). 24,79,80 We further calculated the S k and λ k contribution of each of the vibrational modes involved in the S 1 → S 0 transition (Fig. 3i and j), in which the promoting modes associated with the k S NR of TDBA-Ac and PzTDBA are illustrated in Fig.…”