Oligomeric Polysiloxanes with Tunable Emission Colors from Blue to Yellow

Developing long-wavelength emissive nontraditional fluorescent polymers remains a big challenge. Herein, we synthesized four types of oligomers (HP1-HP4) that exhibit different fluorescence colors by introducing tertiary amines and C═C using a simple transesterification polycondensation method. Intriguingly, pure HP1 containing C═C and tertiary amines emits blue, yellow green, and yellow fluorescence under the irradiation of various excitation lights, showing color-tunable emission characteristics. Compared with HP3 with only C═C groups in its main chain, the optimal excitation/emission wavelength of HP1 in solution and pure states red-shifted to 520/550 and 525/554 nm, respectively. Experimental results and theoretical calculations revealed that the formation of efficient through-space n-n and n-π interactions leads to fluorescence. The presence of tertiary amines and C═C decreases the HOMO-LOMO gap of the oligomers and makes them easy to excite, which results in the red-shifted fluorescence. The prepared oligomers show excellent applications in information encryption and luminescent hydrogel preparation.