Minimizing the Electron Donor Size of Donor–Acceptor-Type Photosensitizer: Twisted Intramolecular Charge-Transfer-Induced Triplet State and Singlet Oxygen Formation

Abstract

Efficient and selective heavy atom-free singlet oxygen photosensitizers (HAFPS) are highly desirable for chemistry, pharmaceutical sciences, phototherapy, and environmental sciences. The donor–acceptor (D–A)-type HAFPS based on charge transfer/charge recombination mechanism usually requires that a photosensitizing chromophore A (such as boron dipyrromethene (BODIPY)) is attached by a large and perpendicular aryl donor D in its ground state. In this report, however, we show that much smaller non-aryl dialkylamino donors also enable BODIPY to generate singlet oxygen and excited triplet state selectively and very efficiently in nonpolar media. The mechanism is that the photoexcitation of NR2-BODIPY leads to the twisting of the NR2 so that a vertical geometry is formed, which best facilitates T1 formation via intramolecular charge transfer/charge recombination processes. This small NR2 group modification does not need any aryl (pyrenyl, anthracyl, BODIPY, naphthyl, and phenyl) to enhance the intersystem crossing; therefore the synthesis is very facile and the material is atom-economic. The synthesis contains neither halogen atoms nor heavy metal ions so that this novel strategy provides more environment- and health-friendly singlet oxygen photosensitizers for use in chemical synthesis, pharmaceutical sciences, phototherapy, environmental sciences, and physiology.

Release of CO and Production of 1O2 from a Mn-BODIPY Photoactivated CO Releasing Molecule with Visible Light

“…This peak is assigned as the triplet excited state ( 3 ππ*) of the bpy-I-BDP ligand. , The energies of these triplet excited states were measured as 1.61 and 1.58 eV for bpy-I-BDP and Mn-bpy-I-BDP, respectively. The higher energy levels of these triplet excited states compared to the energy required for producing singlet oxygen (0.98 eV) are consistent with the production of singlet oxygen by energy transfer. , …”

“…The higher energy levels of these triplet excited states compared to the energy required for producing singlet oxygen (0.98 eV) are consistent with the production of singlet oxygen by energy transfer. 71,72 Computational Studies: Time-Dependent DFT. We further studied the involved electronic transitions and absorption spectra of our compounds with time-dependent DFT (TD-DFT) at the B3LYP level using SDD pseudopotentials for Mn, I, and Br and 6-311G(d) basis set for other elements.…”

Exploiting a Neutral BODIPY Copolymer as an Effective Agent for Photodynamic Antimicrobial Inactivation

“…If population of the triplet state occurs via a singlet fission mechanism, the persistent triplet absorption may initially involve spin-correlated triplet pairs. Alternatively, as described in recent studies, twisted intramolecular charge-transfer states may be involved as precursors to the triplet state. , …”

“…Alternatively, as described in recent studies, twisted intramolecular charge-transfer states may be involved as precursors to the triplet state. 74 , 75 …”

Broadband Visible Light-Absorbing [70]Fullerene-BODIPY-Triphenylamine Triad: Synthesis and Application as Heavy Atom-Free Organic Triplet Photosensitizer for Photooxidation

“…PSs without heavy atoms usually suffer from the unpredictable ISC ability. In order to address the aforementioned problems, strategies such as using a twisted π-conjugation system [ 16 , 17 ], singlet fission [ 18 , 19 ], spin–orbit charge transfer [ 20 , 21 ], and radicals [ 22 , 23 ] have been developed to enhance the ISC of heavy atom-free PSs. However, the synthetic methods of these compounds are highly demanding.…”