Thermochromic Luminescent Materials and Multi-Emission Bands in d10 Clusters

Adamantane-type clusters: compounds with a ubiquitous architecture but a wide variety of compositions and unexpected materials properties

The research into adamantane-type compounds has gained momentum in recent years, yielding remarkable new applications for this class of materials. In particular, organic adamantane derivatives (AdR4) or inorganic adamantane-type compounds of the general formula [(RT)4E6] (R: organic substituent; T: group 14 atom C, Si, Ge, Sn; E: chalcogenide atom S, Se, Te, or CH2) were shown to exhibit strong nonlinear optical (NLO) properties, either second-harmonic generation (SHG) or an unprecedented type of highly-directed white-light generation (WLG) - depending on their respective crystalline or amorphous nature. The (missing) crystallinity, as well as the maximum wavelengths of the optical transitions, are controlled by the clusters' elemental composition and by the nature of the organic groups R. Very recently, it has been additionally shown that cluster cores with increased inhomogeneity, like the one in compounds [RSi{CH2Sn(E)R'}3], not only affect the chemical properties, such as increased robustness and reversible melting behaviour, but that such 'cluster glasses' form a conceptually new basis for their use in light conversion devices. These findings are likely only the tip of the iceberg, as beside elemental combinations including group 14 and group 16 elements, many more adamantane-type clusters (on the one hand) and related architectures representing extensions of adamantane-type clusters (on the other hand) are known, but have not yet been addressed in terms of their opto-electronic properties. In this review, we therefore present a survey of all known classes of adanmantane-type compounds and their respective synthetic access as well as their optical properties, if reported.

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

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 (CH₃NH₃)₄Cu₂Br₆ thin films with a zero-dimensional molecular salt structure featuring "isolated" [Cu₂Br₆]^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 [Cu₂Br₆]^4- anion and the (CH₃NH₃)₄Cu₂Br₆ crystal suggest a strong impact of the crystal environment on the structure of the anion.

Fluorochromic polymer films containing ultrasmall silver nanoclusters

Fluorochromic materials that change their emission properties in response to their environment are of interest for the development of sensors, optical data storage and light-emitting materials. A thermally fluorochromic elastic polymer film that exhibits remarkable fluorochromism (from red to yellow) and enhancement of fluorescence intensity after thermal treatment (>120 °C) is designed by the incorporation of silver nanoclusters. The thermal treatment also leads to a significant increase of quantum yield and fluorescence lifetime. It is found that the thermo-induced etching on larger silver nanoclusters generates smaller silver nanoclusters. This simple and efficient size-tuning process in solid state is responsible for the thermo-fluorochromism and enhancement of fluorescence emission from silver nanoclusters. Such a thermo-fluorochromic polymer material is finally demonstrated to be useful for thermo-printing. This material illustrates a new way to make smart optical materials, particularly for potential applications in optical data storage and soft OLED display.

A copper(i) bromide organic–inorganic zwitterionic coordination compound with a new type of core: structure, luminescence properties, and DFT calculations

A new organic–inorganic Cu(i) bromide complex based on protonated tris(2-pyridyl)phosphine, [(HPy)₃PCu₂Br₅], has been synthesized by a straightforward reaction in solution or by modification of the [Cu₂Br₂(Py₃P)₂] complex using hydrobromic acid.

Synthesis of dual emitting iodocuprates: can solvents switch the reaction outcome?

An unprecedented structure-directing effect of solvents in halocuprate self-assembly reactions was discovered. The compounds presented show remarkable dual luminescence, strongly changing the emission color upon varying temperature.

Exploring Organic Metal Halides with Reversible Temperature-Responsive Dual-Emissive Photoluminescence

The exceptional structural tunability of organic metal halides endows them with fascinating electronic and photophysical properties, providing much scope for applications. In this work, single crystals of the organic metal halide (C₄ H₉ NH₃ )₂ MnI₄ are found to show reversible thermo-induced luminescent chromism within a wide temperature range. The (C₄ H₉ NH₃ )₂ MnI₄ single crystal exhibits two emission peaks at 550 and 672 nm, which are assigned to a d-d transition of Mn²⁺ -centered tetrahedra and self-trapped excitons, respectively. The temperature-dependent emission color change is attributed to the thermo-induced trapping and detrapping process of the self-trapped exciton. (C₄ H₉ NH₃ )₂ MnI₄ exhibits a maximum photoluminescence quantum efficiency of up to 68 % at 70 °C. The disclosed interacted photoluminescence decay mechanisms may prove useful for the further design of organic metal halides for optical thermometry.