The emission of AntBDP 1c in toluene shows a similar CT fluorescence at 625 nm (Figure ). The Φem values decreases considerably from 0.225 for nonpolar hexane to 0.04 in ACN. This can be rationalized by taking into account lower reduction potential of 9-methylanthracene fragment (1.04 eV), compared to pyrene, which increases the driving force of the electron transfer process making it favourable in less polar solvent such as toluene. Previously reported BODIPY-anthracene dyads, which have no substituents in the 2,6 positions, form CT states in more polar solvents such as ACN and DCM. It is likely that the CT emission quantum yield for 1c is significantly lower, making it difficult to observe from emission spectra. For compounds 1e-g containing different number of methoxy substituents in the meso-phenyl group, the absorption spectra show strong S0 → S1 transitions at around 500 nm, with slight red shifts of 6 -9 nm as solvent polarity increases. There is also S0 → S2 transitions at ≈ 350 nm from the phenyl subunit, indicating that the electronic coupling with the BODIPY core in the ground state is weak. Upon changing the solvent polarity, the shape and maxima of the absorption and emission bands of 1e-g undergo little change. However, changes can be seen in the emission quantum yields (Φem), particularly for 1f where Φem varies from <0.001 in EtOH up to 1 in hexane. As the dyads have the same ethoxycarbonyl-substituted core, the difference in emission yields between 1e, 1f and 1g must be due to the changes in methoxysubstituents in the meso-phenyl group. Φem values show stronger solvent polarity dependence for 1f and 1g than for 1e, which could relate to the latter having substituents in the ortho-position of the phenyl ring. This can also be explained by the oxidation potentials (Eox) of the meso-methoxybenzene substituents, which are: 1.77 for anisole (1e), 1.55 for 1,3-dimethoxybenze (1f) and 1.54 for 1,3,5-trimethoxybenzene (1g). The more methoxy-substituents present on the phenyl ring, the lower the Eox of the group and thus better electron-donating capabilities. The placement of these methoxy groups on the phenyl could also potentially hinder the rotation of the meso-aryl donor group, making the geometry of the dyad orthogonal and in turn promoting SOCT-ISC. To assess the efficiency of triplet state formation in different solvents, the singlet oxygen quantum yields were determined through a chemical-trapping method, employing 1,9dimethylanthracene (DMA) as a 1 O2 sensor. DMA selectively reacts with singlet oxygen giving a corresponding endoperoxide. For the measurements, solutions of DMA in air-saturated solvent containing corresponding BODIPY were irradiated with light at 514 nm with a constant 12 mW cm -2 power for periods of 30 -120 s, after which the absorption spectra were recorded. The BODIPY absorption shows no change during irradiation, while the DMA absorption decreases linearly over time (Figure , inset). This a Concentration of the samples: 5 × 10 -6 M. Absorption maxima corresponding to BODIPY chromophore. Fluorescence was recorded by exciting the samples at the vibrational shoulder of the BODIPY absorption. Excitation wavelength: 470 nm. The fluorescence quantum yields were measured using Rhodamine 6G as a standard (Φem = 0.95 in EtOH). Represents the integral emission coming from LE and CT excited states. HEX -hexane, TOL -toluene, THFtetrahydrofuran, DCM -dichloromethane, EtOH -ethanol, ACN -acetonitrile.