We hypothesized that the internal conversion between T 2 and T 1 could be slowed or even inhibited through the use of a nonconjugated sp 3 carbon atom to electronically isolate donor and acceptor groups (Cz-C-PTZSO 2 and Cz-C-TRZ), where multiple RTP would originate from both donor and acceptor subunits (Figure ). For sp 2 C-linked species (Cz-CO-PTZSO 2 and Cz-CO-TRZ), due to the stronger electronic communication between the donor and acceptor, the internal conversion of excitons between T 2 and T 1 is greatly enhanced, resulting in only phosphorescence from T 1 . To substantiate this hypothesis, we first modelled the photophysical properties of these four compounds in the gas phase using density functional theory (DFT) at the PBE0 49 /6-31G(d,p) level. From Figure , the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of Cz-C-PTZSO 2 and Cz-C-TRZ are localized on the donor (Cz-Ph) and acceptors (PTZSO 2 and TRZ), showing near-zero frontier molecular orbital (FMO) overlap. For Cz-CO-PTZSO 2 and Cz-CO-TRZ, the LUMO is delocalized across both the acceptor and the benzophenone core, resulting in deeper HOMO and LUMO levels (Figure ). Time-dependent DFT calculations at the same level of theory demonstrate a relatively large energy gap between S 1 and T 1 (DE ST ) in these compounds (Figure ), indicating that these compounds should not exhibit thermally activated delayed fluorescence (TADF). Given the presence of multiple triplet excited energy levels serving as upper receiver states and moderate spin-orbital coupling (SOC) constants (Figure ), RTP should be theoretically favored as the dominant radiative decay process. The T 1 and T 2 energies of Cz-C-PTZSO 2 and Cz-C-TRZ are almost degenerate with those of the T 1 energies of the isolated donor, Cz-Ph, and acceptors, PTZSO 2 and TRZ (Figure ). For Cz-CO-PTZSO 2 and Cz-CO-TRZ, similar T 1 energies imply that both states have the same character, which is close to that of the LE T 1 state of carbazole-benzophenone (Cz-BP) subunit (Figure ). Furthermore, the excitonic coupling between T 1 and T 2 was investigated based on the hole-electron distribution analysis using the Multiwfn program. 51 Cz-C-PTZSO 2 and Cz-C-TRZ both show decoupled T 1 and T 2 (Figure ), where the hole (green) and electron (blue) distributions are identical to those of donor (as T 1 for Cz-C-PTZSO 2 ; as T 2 for Cz-C-TRZ) and acceptor (as T 2 for Cz-C-PTZSO 2 ; as T 1 for Cz-C-TRZ) (Figure ), implying that if there is poor communication between the two states then dual phosphorescence may be enabled from emission from each of the donor and acceptor groups. However, Cz-CO-PTZSO 2 and Cz-CO-TRZ exhibit strongly coupled triplet excited states due to the overlap of the hole and electron densities, and the small energy gap between T 2 and T 1 , demonstrating the occurrence of a rapid internal conversion between T 2 and T 1 . T 1 spin density distributions reveal that in Cz-C-PTZSO 2 and Cz-C-TRZ they are very localized on Cz-Ph (Figure ), while for Cz-CO-PTZSO 2 and Cz-CO-TRZ the spin densities are relatively delocalized (Figure ), similar to the hole-electron density distribution analysis (Figure ). The energies of frontier molecular orbitals (FMOs) were inferred from the oxidation and reduction potentials (E ox /E red ), obtained using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in deaerated DMF with 0.1 M [ n Bu 4 N]PF 6 as the supporting electrolyte. The E ox /E red values of Cz-C-PTZSO 2 , Cz-CO-PTZSO 2 , Cz-C-TRZ and Cz-CO-TRZ, determined from the DPV peaks, are 1.31/-2.32 V, 1.42/-1.52 V, 1.23/-1.73 V and 1.41/-1.18 V, respectively, vs SCE (Figure , Table ). The corresponding HOMO/LUMO values are -5.66/-2.03 eV, -5.77/-2.83 eV, -5.57/-2.62 eV and -5.76/-3.17 eV, We next investigated the photophysical properties of the Cz-C-PTZSO 2 and Cz-CO-PTZSO 2 crystals, which were isolated from a toluene solution. The photophysical data are summarized in Table . The steady-state PL spectrum of Cz-C-PTZSO 2 in air at 298 K shows a structured locally excited (LE) emission profile with maxima, l PL , at 403 nm and 426 nm, alongside a broad emission tail (Figure ). The corresponding PL lifetime is ~3.5 ns recorded both at 403 nm and 426 nm (Figure ).