This minireview is devoted to honoring the memory of Dr. Thomas Dougherty, a pioneer of modern photodynamic therapy (PDT). It compiles the most important inputs made by our research group since 2012 in the development of new photosensitizers based on BODIPY chromophore which, thanks to the rich BODIPY chemistry, allows a finely tuned design of the photophysical properties of this family of dyes to serve as efficient photosensitizers for the generation of singlet oxygen. These two factors, photophysical tuning and workable chemistry, have turned BODIPY chromophore as one of the most promising dyes for the development of improved photosensitizers for PDT. In this line, this minireview is mainly related to the establishment of chemical methods and structural designs for enabling efficient singlet oxygen generation in BODIPYs. The approaches include the incorporation of heavy atoms, such as halogens (iodine or bromine) in different number and positions on the BODIPY scaffold, and also transition metal atoms, by their complexation with Ir(III) center, for instance. On the other hand, low‐toxicity approaches, without involving heavy metals, have been developed by preparing several orthogonal BODIPY dimers with different substitution patterns. The advantages and drawbacks of all these diverse molecular designs based on BODIPY structural framework are described.

In this work, hemicyanine dye LDS 722 is encapsulated into the 1D elliptical nanochannels of MgAPO‐11 aluminophosphate by a crystallization inclusion method. The synthesis of the hybrid material has been optimized through a systematic variation of the crystallization conditions in order to obtain pure and large crystals (around 20 μm×30 μm) suitable for optical applications. The tight fitting between the molecular size of the guest dye and the pore dimensions of the host has favored a rigid planar conformation of the dye, restricting its inherent flexibility, which is confirmed by molecular simulations. Consequently, the encapsulation of LDS 722 into MgAPO‐11 has led to an astonishing enhancement of the fluorescence with respect to the dye into MgAPO‐5, with slightly larger cylindrical channels, and with respect to the dye in solution. Moreover, the perfect alignment of LDS 722 (dye with intrinsic nonlinear‐optical properties) along the channels of MgAPO‐11 has revealed attractive second‐order nonlinear properties, such as second harmonic generation, proven through microscopy measurements in single crystals.

The detailed triplet and singlet state characterization of 3,5-dimethyl-2,6-diiodo-8-thiomethyl-pyrromethene (MeSBDP), a promising standard sensitizer for singlet oxygen production.

Biscyclometalated Ir complexes involving boron-dipyrromethene (BODIPY)-based ancillary ligands, where the BODIPY unit is grafted to different chelating cores (acetylacetonate for Ir-1 and Ir-2, and bipyridine for Ir-3) by the BODIPY meso position, have been synthesized and characterized. Complexes with the BODIPY moiety directly grafted to acetylacetonate (Ir-1 and Ir-2) exhibit higher absorption coefficients (ϵ≈4.46×10 m cm and 3.38×10 m cm at 517 nm and 594 nm, respectively), higher moderate fluorescence emission (φ ≈0.08 and 0.22 at 528 nm and 652 nm, respectively) and, in particular, more efficient singlet oxygen generation upon visible-light irradiation (φ ≈0.86 and 0.59, respectively) than that exhibited by Ir-3 (φ ≈0.51, but only under UV light). Phosphorescence emission, nanosecond time-resolved transient absorption, and DFT calculations suggest that BODIPY-localized long-lived IL states are populated for Ir-1 and Ir-2. In vitro photodynamic therapy (PDT) activity studied for Ir-1 and Ir-2 in HeLa cells shows that such complexes are efficiently internalized into the cells, exhibiting low dark- and high photocytoxicity, even at significantly low complex concentration, making them potentially suitable as theranostic agents.

A cyanine dye (PIC) was occluded into two 1D-nanopoporus Mg-containing aluminophosphates with different pore size (MgAPO-5 and MgAPO-36 with AFI and ATS zeolitic structure types, with cylindrical channels of 7.3 Å diameter and elliptical channels of 6.7 Å × 7.5 Å, respectively) by crystallization inclusion method. Different J-aggregates are photophysically characterized as a consequence of the different pore size of the MgAPO frameworks, with emission bands at 565 nm and at 610 nm in MgAPO-5 and MgAPO-36, respectively. Computational results indicate a more linear geometry of the J-aggregates inside the nanochannels of the MgAPO-36 sample than those in MgAPO-5, which is as a consequence of the more constrained environment in the former. For the same reason, the fluorescence of the PIC monomers at 550 nm is also activated within the MgAPO-36 channels. Owing to the strategic distribution of the fluorescent PIC species in MgAPO-36 crystals (monomers at one edge and J-aggregates with intriguing emission properties at the other edge) an efficient and one-directional antenna system is obtained. The unidirectional energy transfer process from monomers to J-aggregates is demonstrated by remote excitation experiments along tens of microns of distance.

The versatility in the synthesis of BODIPY derivatives in terms of functionalization is further demonstrated. In particular, in this work β-β'-BODIPY dimers with varied functional groups in the meso positions were synthesized in very efficient yields and short reaction times from a single platform. A photophysical study was carried out in all of the compounds. The resultant dimers show absorption bands at around 600 nm as a consequence of electronically coupled monomers disposed with a dihedral angle of around 30°, which is supported by theoretical simulations. The emission properties of these molecules are distinguished by the appearance of an ICT state as the polarity of the solvent increases.

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