The effects of supramolecular encapsulation on the photophysics and photostability of a highly fluorescent dimeric derivative of 2,6-diacetox-y-9,10-bis(arylethynyl)anthracene (G2) were investigated by single-molecule fluorescence spectroscopy (SMFS). The fluorescence properties of free-G2 and its self-assembled boronic ester encapsulation complex, G2@(Cap)(2), were compared in solution and a glassy polymer film. The fluorescence spectral characteristics and theoretical calculations suggest that the environment affects the excited-state conformation and subsequent fluorescence emission of G2@(Cap)(2). In particular, in the liquid and polymer environments, G2@(Cap)(2) emits a fluorescence photon in the planar and twist conformation, respectively, whereas the fluorescence-emitting conformation of free-G2 is planar in both environments. The luminous conformation differences between free-G2 and G2@(Cap)(2) in polymer are reflected in the intersystem crossing (ISC) parameters (the ISC quantum yield and triplet lifetime), as determined by fluorescence autocorrelation analysis. The photobleaching yield revealed a 3-fold enhancement in the photostability of encapsulated G2 (relative to free-G2). Under the SMFS measurement conditions, the photostability of the encapsulation complex was independent of the guest's photostability and appeared to be dominated by the thermal stability of the Cap host molecule.