Polymorphism-Mediated Regulation of Thermally Activated Delayed Fluorescence and Room-Temperature Phosphorescence via Intra- and Intermolecular Charge Transfer

Abstract

Even though there is a vast library of self-assembled organic molecules offering practically infinite possibilities to produce thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP), obtaining both from a single candidate is a formidable challenge due to the difficulty in controlling the excited-state dynamics. Here, we demonstrate how a single polymorphic molecule with a donor−acceptor−donor (D−A−D) architecture can be used to regulate both TADF and RTP with the help of polymorph engineering. Thermodynamically controlled macrocrystals show TADF due to intermolecular charge transfer (inter-CT), which reduces the singlet−triplet energy gap (ΔE S−T ), enhances reverse intersystem crossing (RISC), and boosts the delayed singlet radiative decay. The energy gap in kinetically controlled self-assembled microcrystals is greater due to larger intermolecular distance and hence weaker inter-CT. On the other hand, the presence of stronger intramolecular charge transfer (intra-CT), in addition to restricted RISC in the microcrystals, stabilizes the triplet excitons to favor RTP.

Supramolecular crystals of Mn(15-crown-5)(MnCl4)(DMF) with dielectric phase transition, high quantum yield and phase transition-induced luminescence enhancement behavior

“…The thermally activated delayed fluorescence is commonly observed in thermally activated delayed fluorescence systems, where the emission intensity tends to be enhanced with an increase in temperature. 41–47 In addition, the maximum of the emission band shifts slightly to the blue side at temperatures above 340 K compared to that below 340 K. The coordination environment of the MnCl 4 2− anion and the Mn(15-crown-5) 2+ cation was inspected in the three phases, as depicted in Table 1. In the LTP, the Mn–Cl bond lengths range from 2.341 to 2.416 Å, with an average value of 2.366 Å.…”