Excited-State Dynamics of Bis(tetraethylammonium) Di-µ-bromo-dibromodicuprate(I) Thin Films

Organic-inorganic halocuprates based on monovalent copper are promising luminescent compounds for optoelectronic applications; however, their relaxation processes in the excited electronic state are severely underexplored. In this contribution, we prepare thin films of bis(tetraethylammonium) di-µ-bromo-dibromodicuprate(I) [N(C₂H₅)₄]₂[Cu₂Br₄], abbreviated (TEA)₂Cu₂Br₄, which features a "molecular salt" structure containing discrete [Cu₂Br₄]^2- anions. This compound, which has an absorption peak at 283 nm, displays a blue, strongly Stokes-shifted emission with a peak at 467 nm. Transient photoluminescence (PL) experiments using broadband emission detection and time-correlated single-photon counting (TCSPC) both find an excited-state lifetime of 57 μs at 296 K. UV-Vis transient absorption experiments at 296 K covering time scales from femto- to microseconds provide evidence for the formation of the T₁ state through intersystem crossing from S₁ with a time constant of 184 ps. The triplet state subsequently decays to S₀ predominantly by phosphorescence. In addition, the time constants for carrier-optical phonon scattering (1.8 ps) and acoustic phonon relaxation (8.3 ns and 465 ns) of (TEA)₂Cu₂Br₄ are provided.