Organic Crystal with Anti-Stokes Photoluminescent Excitation and Thermally Activated Delayed Fluorescence Features

Abstract

Thermal activation process utilizes environmental thermal energy to help supplement energy for the nonspontaneous energy-consuming upconversion physical transitions with positive free energy change (ΔG > 0). Reverse intersystem crossing (rISC) and hot band absorption are two kinds of thermal activation transitions. Thermally activated delayed fluorescence (TADF) materials with rISC have significantly propelled advancements in organic semiconductors. Hot band absorption, enables anti-Stokes photoluminescence, offering a promising route for efficient photon upconversion. In this work, we constructed a crystal consisting of a donor-acceptor type TADF molecule, DPQ-DPAC, demonstrating dual thermal activation properties of hot band absorption with a notable 0.1 eV anti-Stokes shift emission and proficient TADF performance. Only in the crystal TADF efficiency facilitates and the photoluminescence quantum yield elevates to an impressive 90.8%. Combining the extended absorption spectrum, these enhancements collectively realize anti-Stokes photoluminescence in crystal. Experimental and theoretical results on the DPQ-DPAC crystal indicate optimizations in its conformational and vibrational modes, resulting in enhancements to its properties. This finding provides insight into crafting organic materials with thermally activated functionalities and contributes to fully exploiting the potential of organic materials, further advancing versatile materials applications.

Keywords: Anti-Stokes Photoluminescence; Hot Band Absorption; organic crystal; thermally activated delayed fluorescence.