Recently, three 9,9-dimethylxanthene-based donor (D)/acceptor (A) U-shaped space-through architectures, containing π–π intramolecular interactions between the D and A, exhibit unique advantage (i.e., a small singlet (S1) – triplet (T1) energy splitting (ΔEST)) in thermally activated delayed fluorescence (TADF). To explore the TADF and second-order nonlinear optical (NLO) properties of U-shape compounds with through-space charge transfer (TSCT) between aligned D and A units compared with that of conventional conjugated D–A (L shape) ones, we theoretically investigated the geometric and electronic structures, through space D–A π–π interactions, CT properties, ΔEST, and first hyperpolarizabilities (βtot) of compounds 1-L∼5-U. The calculated ΔESTvalues of the U-shaped molecules are relatively smaller than that of L-shaped compounds in gas phase, indicating that the U-shaped derivatives are excellent thermally activated delayed fluorescent candidates. Furthermore, a noteworthy finding was that the conjugated D–A unit of L-shaped compounds was suggested to promote the performance in NLO due to the lower excited energy and stronger oscillator strength for the crucial excited state. Especially, for compound 2-L, the βtotvalue is 8 times larger than that of 2-Uin gas phase. In addition, we have quantitatively studied ΔESTand βtotvalues in the solid-state polarization for all studied molecules using the polarizable continuum model. Importantly, the results of polarization effects (ε from 1.0 to 3.0) show that the marked reduction in the ΔESTvalues of U-shaped derivatives are due to the simultaneous presence of dominant 1TSCT and 3TSCT excited states in the solid-state polarization, which are favorable for TADF materials. In addition, the increment in the βtotvalues of L-shaped compounds are preferable for NLO applications. We hope this work may provide a theoretical understanding on the influence of the heteroatom and the π–π conjugation between D and A units and polarization effects on the ΔESTand βtotand novel design mentality of the efficiency-enhancing TADF and NLO materials.