Photon upconversion (UC) based on triplet–triplet annihilation (TTA) has drawn increasing attention in recent years, primarily because of its occurrence with low-intensity, noncoherent light as the excitation source. TTA-UC process occurs in association with a series of photochemical events. To date, efficient TTA-UC has been achieved for molecularly dispersed solutions, because they allow fast diffusion of excited molecules. However, the use of volatile organic solvents hampers the development of TTA-UC and their real world applications, and thus it is of obvious significance to develop solid-state TTA-UC systems. Although amorphous polymeric films have been employed as solid matrix, they inevitably restricted the diffusion of excited triplet molecules, resulting in the undesired use of high-power incident light to ensure effective concentration of excited triplets. Organic crystals, meanwhile, provide another class of solid systems which are attractive since they allow mobility of excitons among crystalline lattice. Particularly good candidates are the molecules showing aggregation-induced emission (AIE) or aggregation-induced enhanced emission (AIEE), because they are highly emissive even in the neat crystalline state. In addition, the changes of optical properties by aggregation would give TTA-UC a dynamic controllability. However, the AIE phenomena have been naturally focused on the excited singlet states of molecular aggregates, while their correlations to TTA-UC have been unprecedented. Here we report the first example of aggregation-induced photon upconversion (iPUC) which is based on the controlled potential energy landscape of excited triplet state. As a proof of concept, we employed one of the best-known structural motifs for AIE, cyano-substituted oligo(p-phenylenevinylene), as acceptor. When a triplet state of this acceptor was populated by triplet sensitizer in solution, the TTA-UC emission was not observed. In contrast, by drying this mixed solution, the resulting crystalline sample showed clear UC emission. Theoretical studies and control experiments unveiled an underlying mechanism; an enhanced conformational twisting around the double bond and photoisomerization in the excited state (T1) results in immediate intersystem crossing to the ground state (S0) in solution, and this large structural change is effectively prohibited in the solid state. This difference in energy landscape of excited triplet states between solution and solid states was further amplified through the TTA process, leading to a novel ON/OFF switching mechanism for UC emission. Meanwhile, since the UC emission requires two triplet excitons to meet, the complete OFF state can be realized in common excitation power regime. It indicates that by tuning the molecular cohesion force and even by introducing attractive intermolecular interactions between donors and acceptors, it might possible to develop more efficient TTA-UC (or iPUC) in the solid state. We envisage this iPUC systems may lead to dynamic control on the triplet energy landscape and consequent regulation of multi-excitation processes.