Boosted phosphorescence: minor structural changes drastically improve the photoluminescence properties of these new rhenium complexes vs. parent compound.
These easily-prepared rhenium(i) complexes are strongly luminescent in the solid state. In particular, the adamantyl derivative is a promising candidate in the field of optical materials.
Mechanoresponsive luminescence (MRL)m aterials promises mart devicesf or sensing, optoelectronics and security.Wepresenthere the first report on the MRL activity of two Re I complexes,o pening up new opportunities for applicationsi nt hese fields. Both complexese xhibitm arked solidstate luminescence enhancement (SLE). Furthermore, the pristinem icrocrystalline powders emit in the yellow-green region,a nd grinding led to an amorphous phase with concomitant emission redshift and shrinking of the photoluminescence (PL) quantum yields and lifetimes. Quantum chemical calculations revealed the existenceo ftwo low-lying triplet excited states with very similar energy levels, that is, 3 IL and 3 MLCT,h aving, respectively,a lmost pure intraligand (IL) and metal-to-ligand charge-transfer (MLCT) character.T ransi-tion between these states could be promoted by rotation aroundt he pyridyltriazoleÀphenylbenzoxazole bond. In the microcrystals, in which rotations are hindered, the 3 IL state induces the prominent PL emission at short wavelengths. Upon grinding, rotation is facilitated and the transitiont o the 3 MLCT state resultsi nal arger proportiono fl ong-wave-lengthP L. FTIR andv ariable-temperature PL spectroscopy showed that the openingo ft he vibrationalm odes favours non-radiative deactivation of the triplet states in the amorphousp hase. In solution, PL only arises from the 3 MLCT state.T he same mechanism accounts fort he spectroscopic differences observed when passing from crystalst oa morphousp owders, and then to solutions, thereby clarifying the link between SLE and MRL for these complexes.
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