Excitation‐Wavelength‐Dependent Emission and Delayed Fluorescence in a Proton‐Transfer System

Abstract

Manipulating the relaxation pathways of excited states and understanding mechanisms of photochemical reactions present important challenges in chemistry. Here we report a unique zinc(II) complex exhibiting unprecedented interplay between the excitation-wavelength-dependent emission, thermally activated delayed fluorescence (TADF) and excited state intramolecular proton transfer (ESIPT). The ESIPT process in the complex is favoured by a short intramolecular OH⋅⋅⋅N hydrogen bond. Synergy between the excitation-wavelength-dependent emission and ESIPT arises due to heavy zinc atom favouring intersystem crossing (isc). Reverse intersystem crossing (risc) and TADF are favoured by a narrow singlet-triplet gap, ΔE ≈10 kJ mol . These results provide the first insight into how a proton-transfer system can be modified to show a synergy between the excitation-wavelength-dependent emission, ESIPT and TADF. This strategy offers new perspectives for designing ESIPT and TADF emitters exhibiting tunable excitation-wavelength-dependent luminescence.

Recent Advances in Solid‐State Lighting Devices Using Transition Metal Complexes Exhibiting Thermally Activated Delayed Fluorescent Emission Mechanism

“…Bushuev and his team reported a Zn(II) complex ( Zn3 ), exhibiting an interplay between excitation‐wavelength‐dependent emission and TADF in a proton‐transfer system. [ 180 ] Although Zn3 was not used in a lighting device, this was the third zinc(II) complex reported with a TADF emission. Zn3 showed excitation depending luminescence; in fact, when Zn3 was excited between 240–420 nm, a maximum emission was detected at 640 nm with a shoulder at 565 nm and the PLQY of 0.02%.…”

Excitation‐Dependent Emission in All‐Inorganic Lead‐Free Cs2ScCl5·H2O Perovskite Crystals

“…[1][2][3][4][5][6][7] Their emission colors can be tuned simply by adjusting excitation wavelengths, without changing their size DOI: 10.1002/lpor.202100689 or chemical composition. The excitationdependent emission has been observed in metal complexes, [4,8] small molecules, [5,6] polymers, [9] and carbonbased semiconductors. [10,11] Compared with the successful developments in construction of multiple emitting centers in organic materials, the research on singlecomponent inorganic semiconductors with excitation dependent emission is still in infancy.…”

Crystalline Metal‐Organic Materials with Thermally Activated Delayed Fluorescence

“…Thereafter, in 2018, Bushuev's group reported a Zn(II) complex showing TADF. [108] The Zn(II) complex, [Zn(HL)Cl 2 ], was prepared using an excited-state intramolecular proton transfer (ESIPT) 1). Reproduced with permission.…”

“…f-h) Emission decay curves of [Zn(HL)Cl 2 ]. Reproduced with permission [108]. Copyright 2018, Wiley-VCH.…”