Photoinduced Dynamics of (CH₃NH₃)₄Cu₂Br₆ Thin Films Indicating Efficient Triplet Photoluminescence

Abstract

Hybrid organic−inorganic halogenidocuprates based on copper(I) represent materials with rich structural diversity and high photoluminescence (PL) quantum yield, yet the mechanism responsible for their efficient, strongly Stokes-shifted emission is still unclear.Here we report the successful preparation of (CH 3 NH 3 ) 4 Cu 2 Br 6 thin films with a zerodimensional molecular salt structure featuring "isolated" [Cu 2 Br 6 ] 4− ions. Time-resolved broadband PL measurements provide an excited-state lifetime of 114 μs at 298 K. Results from femto-to microsecond UV−vis−NIR transient absorption experiments combined with DFT/ TDDFT calculations suggest the formation of a long-lived structurally relaxed triplet species through intersystem crossing (61 ps), which almost exclusively decays by phosphorescence. In addition, time scales for structural relaxation and cooling processes are extracted from a global kinetic analysis of the transient spectra. Calculations for the isolated [Cu 2 Br 6 ] 4− anion and the (CH 3 NH 3 ) 4 Cu 2 Br 6 crystal suggest a strong impact of the crystal environment on the structure of the anion.

Tuning the Self-Trapped Emission: Reversible Transformation to 0D Copper Clusters Permits Bright Red Emission in Potassium and Rubidium Copper Bromides

“…The 1D chains , in A 2 CuBr 3 and 0D clusters in ACB-DMSO (A = K, Rb) give rise to very different electronic states and optical properties. The blue emission of A 2 CuBr 3 is attributed to STEs while the long-lived red emission of ACB-DMSO (A = K, Rb) likely originates from the triplet decay mechanism that is common for other zero-dimensional metal halides. ,− In ACB-DMSO, the excitation creates a singlet exciton localized at a [Cu 4 Br 4 (OH)­(H 2 O)] − species, and then the intersystem crossing (ISC) leads to the conversion of the singlet exciton to the triplet exciton, which is consistent with the measured long lifetimes, and the slow emission decay is a feature of the spin-forbidden triplet exciton emission . RCB-DMSO has similar structural and optical properties with KCB-DMSO, suggesting that their emission mechanism is the same.…”

Understanding Excited-State Relaxation in 1,3-Bis(N-carbazolyl)benzene, a Host Material for Organic Light-Emitting Diodes

“…For pump−probe experiments up to several microseconds, the samples were excited by the fourth harmonic of a Q-switched Nd:YAG microlaser (Standa-Q1TH, 266 nm), which was electronically synchronized with the amplifier system. 17 The time resolution of these measurements was 420 ps. The fluence of the pump laser beam was adjusted by a combination of a half-wave plate and a polarizer with the help of a calibrated photodiode (Thorlabs S120VC) and a beam profiler (Visulux).…”

Highly Stable Tetrahydrothiophene 1-Oxide Caged Copper Bromide and Chloride Clusters with Deep-Red to Near-IR Emission

“…Upon photoexcitation, electrons are excited from the HOMO to the LUMO. Then, the excited electrons convert from the singlet state (S 1 ) to the lower triplet state (T 1 ) due to the intersystem crossing (ISC). − The formation of the triplet state contains significant structural relaxation of the anion, which can produce broadband red emissions with long lifetimes (Figure ) without the need to resort to self-trapping . The difference in electronegativity and radius between Cl and Br results in the variation in the Cu–X bond distance and lattice distortion; as a result, the [Cu 4 Cl 4 (OH)­(H 2 O)] − and [Cu 4 Br 4 (OH)­(H 2 O)] − clusters have different radiative recombination processes.…”

“…30−32 The formation of the triplet state contains significant structural relaxation of the anion, which can produce broadband red emissions with long lifetimes (Figure 4) without the need to resort to selftrapping. 30 The difference in electronegativity and radius between Cl and Br results in the variation in the Cu−X bond distance and lattice distortion; as a result, the [ The stability of the materials, in addition to the improved PLQY, is the key reason to use THTO as the linking ligand. We examine the air stability and photostability of these redemissive single crystals.…”