Charge Transfer Mediated Triplet Excited State Formation in Donor-Acceptor-Donor BODIPY: Application for Recording of Holographic Structures in Photopolymerizable Glass

Donor–acceptor–donor BODIPY triads bearing anthracene or pyrene as electron donating subunits were prepared through a stepwise synthesis. Photoinduced electron transfer and formation of long-lived triplet excited states via spin–orbit charge transfer intersystem crossing (SOCT-ISC) was studied by steady-state and ultrafast pump-probe spectroscopy and further supported by DFT computations. New BODIPYs were found to form triplet states and sensitize singlet oxygen in both polar and non-polar solvents which is unusual for photosensitizers operating via SOCT-ISC. BODIPY-anthracene triad (ABA) was used as a photosensitizer component in a photopolymerizable glass that was prepared by a four-step sol–gel process. ABA in combination with N-phenylglycin (NPG) showed the ability to initiate a free-radical polymerization of methacrylate monomers under 532 nm irradiation thus allowing for holographic recording of diffractive structures. High diffraction efficiency (up to 87%) obtained for ABA-NPG containing glass as compared to a reference diiodo-BODIPY (I2BDP) demonstrates for the first time that heavy-atom-free SOCT-ISC photosensitizers can efficiently operate in the solid state

Diethoxycarbonyl-BODIPYs as heavy-atom-free photosensitizers for holographic recording in cellulose acetate photopolymer

A series of new heavy-atom-free photosensitizers based on 2,6-diethoxycarbonyl-BODIPY scaffold was designed and applied for holographic recording in a photopolymerizable material. Photoinduced electron transfer between the BODIPY and meso-aryl subunits, followed by the formation of BODIPY triplet excited states via spin-orbit charge transfer intersystem crossing (SOCT-ISC) was studied by steady-state and ultrafast pump-probe transient optical spectroscopy. Highly efficient photosensitization was observed for dyads bearing pyrene and anthracene substituents, which exhibited singlet oxygen generation quantum yields () of up to 94%. Charge transfer and SOCT-ISC were observed in non-polar solvent (toluene) due to the increased electron accepting ability of the diethoxycarbonyl-BODIPY. In combination with N-phenylglycin (NPG) as a co-initiator, new BODIPYs initiate a free-radical polymerization of acrylamide monomers under 532 nm irradiation that was used for creation of volume phase transmission gratings in a photopolymerizable material based on cellulose acetate and polyethylene glycol (CA-PEG). As a result of holographic recording, diffractive structures with diffraction efficiency of up to 56% were obtained for CA-PEG layers sensitized with BODIPY-pyrene dyad as compared to a reference heavy-atom-containing diiodo-BODIPY dye (27%). The developed materials showed refractive index modulation of up to 2.3 × 10-3, which demonstrate the potential of diethoxycarbonyl-BODIPYs photosensitizers for holographic recording applications