Mechanochromic Properties Of Simple Phenothiazine And Triphenylphosphine Derivates With Carbonyl Group

Mechanochromic luminescent materials change their emission colors(spectra)when appropriate pressure or other mechanical force(such as grinding,crushing,rubbing,or extrusion)is applied.These materials can be reverted to their original state by another external perturbation signal(such as heating and fuming).They have recently attracted considerable interests in the field of luminescence switches mechanosensors,optoeletronic devices and data storage.Although many traditional mechanochromic fluorescence materials have been reported,materials involve TADF and phosphorescence is still rare.Small and simple organic molecules has a broader prospect in practical application because of it is easy synthesis and low cost.Therefore,this thesis was focused on the design and synthesis new kind of TADF or phosphorescence mechanochromic materials.Some creative results have been obtained,and outlined below:(1)Nonplanar D–A phenothiazine derivative(PBA),in which phenothiazine and formylphenyl groups act as donor and acceptor,respectively,was designed and synthesized.The PBA emitted weak fluorescence in a solution,and its crystals exhibited weak blue-green emission with a luminescence efficiency of 7.5% under UV light.Quantum chemical calculation indicated that the lowest singlet state was a forbidden n–?* transition both in solution and crystals.Because of the existence of carbonyl,the lowest singlet excited state(S1)could easily transform into triplet states(T1),and then,the luminescence efficiencies were low.However,a grinding crystal provided a powder with strong yellow-green photoluminescence,whose luminescence efficiency increased by a factor of more than 6.Enhanced emission could be ascribed to enhanced thermally activated delayed fluorescence,and the conversion of the S1 state from forbidden S1 of n–?* to allowed S1 of ?–?* induced by the molecule'splanarity under a shearing force.(2)Two simple triphenylphosphine derivatives with formyl(TPPA)and acetyl groups(TPPE)were synthesized.Their luminescence and mechanochromic properties in solution and crystals were studied.Their photoluminescent spectra have two emission bands,the one located at 380 nm is assigned to fluorescence,and the other located at 540 nm is phosphorescence.The luminescence efficiencies of the two compounds in solutions are as low as 1.1% and 1.0% because of the intramolecular rotation of single bonds and quenching by solvents.The intramolecular rotation in the crystal state is suppressed,so they exhibit crystallization-induced emission enhancement.The emissions were enhanced by 6.5 and 27 times,luminescent efficiency reached 7.1% and 26.8%,respectively.The dynamics study indicated that the high luminescence efficiency of TPPE crystal owing to the smaller non-radiative rate.Unfortunately,they did not change the luminescence spectra and colors after grinding,indicating losing of mechanochromic properties.