Defining the origins of multiple emission/excitation in rhenium-bisthiazole complexes

The unusual luminescence behavior of {Re(CO)3}+1-core/thiazole complexes of the type exemplified by the cationic [Re(CO)3{(C3H2SNCH2)2N(CH2)4NH3}]+2 shown above was investigated by fluorescence spectroscopy, x-ray diffraction, DFT calculations and solid state luminescence studies. The relative emission intensities of [Re(CO)3{(C3H2SNCH2)2N(CH2)4NH3}]Br2 (4-BT·HBr) as a 2D grid of excitation vs. emission wavelength are displayed on the contour map. [Display omitted] •Syntheses and structural characterizations of isomers of [Re(CO)3(BT)] bromide.•Spectroscopic characterization: location of triplet states, solid state and low temperature measurements.•DFT calculations confirm that photophysical properties are not due to photoisomerization.•Translation of the unusual emissive behavior to the solid state. The underlying mechanism of the unusual emissive behavior of [Re(CO)3-1,1-bis-4-thiazole-(1,4)-diaminobutane)] bromide (4-BT) has been investigated. Synthesis and spectroscopic characterization of structurally similar isomers ([Re(CO)3-1,1-bis-2-thiazole-(1,4)-diaminobutane)] bromide (2-BT)) and the location of triplet states, solid state and low temperature spectroscopic measurements, and DFT calculations show that the photophysical properties are not due to photoisomerization as previously hypothesized. The results show that the unusual emissive behavior is not observed in structural isomers, is specific to the previously reported complex, 4-BT, and may arise from vibrational energy relaxation and vibrational cooling. Translation of the unusual emissive behavior to the solid state offers an interesting platform allowing this complex to be potentially utilized as a probe, sensor or photonic device.