Dual emission from a single molecule is against the Kasha’s rule. Reports on dual emission behaviors remain sparse in the literature, particularly for low-symmetric organic molecules. We designed a series of fluorescent molecular dyads consisting of a donor (D) and an acceptor (A). The DA dyads involved anthracene (An) or biphenylene (BP) as non-amino donors, and pyrazinoquinoxaline (PQ) or benzoquinoxaline (BQ) as acceptors (AnPQ, BPPQ, AnBP, and BPBQ). The sigma bond bridge between the bulky D and A units conferred a large conformational stain, suppressing rotational motion. Among the orthogonally disposed DA dyads, AnPQ and BPPQ displayed dual emission in organic solutions, with no delayed fluorescence observed. The absence of dual emission in solid states indicated twisted intramolecular charge-transfer (TICT) being responsible for the dual emission. Quantum chemical calculations based on time-dependent density functional theory suggested a pivotal role of the exchange energy gap (EST) between the singlet TICT state and triplet states, including the triplet local excited state in A and the triplet TICT state. We envisioned that our dual-emissive dyads will be useful in bioimaging applications. |