The ring-closure and ring-opening photokinetics were recorded by means of a UV-visible spectroscopy set-up. The resulting absorption time-profiles under continuous irradiation at 365 nm and 575 nm respectively were analyzed numerically, providing the photochromic quantum yields o→c and c→o for 1 and 2, as listed in Table . The photocyclization quantum yields o→c were found at 0.680.09 and 1.000.08 for 1o and 2o. Such high values of o→c are likely due to the hampered thiophene's rotation that favored the anti-parallel form ratio. The quantum yields corresponding to the cycloreversion reaction (c→o) induced at 575 nm are much lower and very similar for both 1 and 2 (0.0330.002 for 1c and 0.0400.002 for 2c), as commonly observed for such DTE derivatives. The introduction of substituents (Me, t Bu) in the 4-positions of the thiophene rings has shown to be effective in increasing photocyclization quantum yields close to unity. The fluorescence properties of the DTE-based pyrene derivatives 1 and 2 were investigated in solution at room temperature with a concentration of c.a. 10 -6 M, diluted enough to exclude intermolecular excimer (Figure ). The monopyrene compound 2 is non-emissive due to rapid competitive ring-closure reaction triggered by irradiation of UV light, which agrees with the photocyclization quantum yield determined at almost unity. However, the DTE-based bispyrene 1 exhibits excimeric emission (Figure , Table ). The emission spectrum of 1o shows a broad band centered at 490 nm attributed to the intramolecular excimer and corresponding to 5 % of photoluminescence quantum yield (QY). Upon irradiation at 350 nm and reaching the PSS, the solution of 1 shows a decrease of the excimer emission intensity of about 70 % (Figure ). The presence of the pyrene emission (400-450 nm) is likely due to the inevitable small amount of the parallel conformer that likely emits as isolated pyrene. This pyrene's emission cannot originate from 1c because; i) it is expected to be quenched by the closed DTE core, ii) a concomitant increase of the pyrene's emission is not observed upon the photocyclization process. The remaining excimer emission (≈ 30 %) at the PSS is due to the presence of residual open isomers, as the photoconversion is not quantitative (≈ 75 %). Upon irradiation at 580 nm the initial emission spectra is fully recovered.