Thermally activated delayed fluorescence (TADF) benzyl cellulose derivatives (TBC-X), which contained both carbazole (host) and phthalimide-based TADF dye (guest) moieties, were prepared from 2,3-dibenzyl cellulose in high yields. The TBC-X samples were soluble in common organic solvents such as CH2Cl2, CHCl3, THF, and toluene. The photoluminescence spectra of TBC-X spin-coated films had a single emission peak derived only from guest moieties, which indicated efficient energy transfer from the host to guest moieties. The TBC-10 (with a content of host and guest moieties of 93 and 7, respectively) in a spin-coated film had the highest photoluminescence quantum yield of 55.3% and TADF characteristics. A nondoped organic light-emitting diode with TBC-10 as the emitting layer showed green emission (lambda(EL) = 517 nm) and achieved a maximum external quantum efficiency of 5.9%.