Investigation On Properties Of Enhanced Stimulus Responsive Luminescent Materials Based On Phenanthroimidazole Derivative

Stimulus response organic light-emitting materials can change the light-emitting behavior under the stimulation of external factors and are widely used in color-changing paper,fluorescent sensors,optical information storage devices,etc.One problem currently exists is that Off-On materials are relatively rare under external stimuli and there is no in-depth theoretical discussion about them.According to the current research situation,two types of molecules with mechanical and acid-stimulating enhanced luminescent properties were constructed with phenanthrazole and cyanostyrene,and synthesized by Debus–Radziszewski imidazole ring-forming reaction and Knoevenagel condensation reaction.The mechanism of stimulus response is discussed in depth,which provides an important experimental basis for the synthesis of enhanced stimulus response luminescent materials.The specific research results are as follows(1)Enhanced mechanical stimuli responsive luminescent materials have been developed with cyanostyrene sterically connected into the furan bromide-substituted phenantimidazole skeleton.It shows that upon mechanical force stimulation,the materials changes not only in luminous color(from dark yellow to bright yellowish-green),but also in fluorescence intensity with the fluorescence quantum yield increasing sharply from 0.04 % to 2.55 %(~63 times).The experimental results suggest that the existence of the large steric groups can regulate the intersystem crossing process between S1 and T1 in the excited state by adjusting the stacking mode of the molecular structure,with enhanced emission swithching from dark emission of triplet excited states to bright emission of S1 singlet excited state under mechanical stimuli.(2)We have developed a type of Off-On proton-stimulated enhanced luminescent materials with vertical D-A structures.Upon TFA fuming,it shows abnormal enhanced emission with quantum yield increased from 2.05 % to 7.53 % accompanied with emission color chang from dark yellow(583 nm)to bright blue(503 nm).Spectral experimental result and theoretical calculation prove that the enhanced mechanism of proton response is attributed to the transition of the excited state from the vertical CT state(charge transfer)to the LE state(local luminescence),providing an effective strategy for designing Off-On type proton-stimuli responsive materials.Through research on both mechanical grinding and acid stimulation,we have developed two types of smart luminescent materials under new mechanisms,which have made important supplement to stimulating luminescent materials.