Thermally　activated　delayed　fluorescent　(TADF)　materials　have　drawn　widespread　attentions　due　to　their　great　potential　for　practical　applications　in　organic　light-emitting　diodes　(OLEDs).　Deep　understanding　of　the　structure-excited　state-photophysical　property　relationships　is　a　key　to　rationally　design　TADF　emitters.　Herein,　two　new　TADF　molecules,　TBP-DPXZ　and　TBQ-DPXZ,　which　consist　of　locked　(triptycene-fused　dibenzophenazine)　and　unlocked　(triptycene-fused　2,　3-diphenylquinoxaline)　electron-acceptors　respectively　and　phenoxazine　electron　donors　are　reported.　The　comparative　study　reveals　that　the　lock/unlock　strategy　could　substantially　manipulate　the　lowest　locally　excited　(LE)　and　charge　transfer　(CT)　states　of　these　emitters　via　changing　the　acceptor　strength,　structural　rigidity,　and　conjugation　length,　and　in　turn　lead　to　significantly　different　photoluminescence　(PL)　and　electroluminescence　(EL)　performance.　It　is　notable　that　the　unlocked　molecule　TBQ-DPXZ　emits　efficient　green　fluorescence　with　photoluminescence　quantum　yield　of　91%　and　TADF　lifetime　of　3.6　mu　s　in　doped　film.　The　doped　OLED　based　on　TBQ-DPXZ　achieves　an　external　quantum　efficiency　(EQE)　of　25.1%,　a　current　efficiency　(CE)　of　79.7　cd/　A,　a　power　efficiency　(PE)　of　80.0　lm/W,　and　a　maximum　luminance　of　18400　cd/m(2),　which　are　better　than　those　of　the　TBP-DPXZ-based　device　and　are　among　the　best　results　reported　so　far　for　green　TADF-OLEDs.