Organic　room-temperature　phosphorescence(RTP)materials　have　attracted　immense　attention　in　bioimaging　due　to　their　long　emission　lifetime　and　large　Stokes　shift.RTP　materials　with　long　emission　wavelength　can　improve　the　penetration　depth　for　bioim-aging.However,the　design　of　red　persistent　RTP　materials　is　still　challenging.In　this　study,a　fused-ring　structure　has　been　proposed　to　effectively　decrease　the　triplet　energy　level,thus　extending　the　emission　wavelength　of　phosphorescence.In　addition,the　fused-ring　structure　exhibits　a　high　molar　extinction　coefficient(e)and　high　luminescence　efficiency　due　to　the　rigid　structure.A　new　class　of　crystalline　hosts(iminodibenzyl,IDB)are　developed　to　stabilize　the　triplet　excitons　that　are　generated　from　the　fused-ring　molecules.The　maximum　RTP　wavelength　of　doping　materials　can　reach　635　nm　with　a　lifetime　of　9.35　ms.Water-disperse　nanopar-ticles　are　successfully　prepared　for　in　vivo　time-resolved　bioimaging,which　eliminates　the　background　fluorescence　interference　from　biological　tissues.These　reveal　a　delicate　design　strategy　for　the　construction　of　long-wavelength　emissive　RTP　materials　for　high-resolution　bioimaging.