β-Pyrrole Functionalized Push or Pull Porphyrins: Excited Charge Transfer Promoted Singlet Oxygen Generation.

Singlet oxygen (O) producing photosensitizers are highly sought for developing new photodynamic therapy agents and facilitating O-involved chemical reactions. Often singlet oxygen is produced by the reaction of triplet-excited photosensitizers with dioxygen via an energy transfer mechanism. In the present study, we demonstrate a charge transfer mechanism to produce singlet oxygen involving push or pull functionalized porphyrins.

Accelerated Intramolecular Charge Transfer in Tetracyanobutadiene- and Expanded Tetracyanobutadiene-Incorporated Asymmetric Triphenylamine-Quinoxaline Push-Pull Conjugates.

The excited-state properties of an asymmetric triphenylamine-quinoxaline push-pull system wherein triphenylamine and quinoxaline take up the roles of an electron donor and acceptor, respectively, are initially investigated. Further, in order to improve the push-pull effect, powerful electron acceptors, viz., 1,1,4,4-tetracyanobutadiene (TCBD) and cyclohexa-2,5-diene-1,4-diylidene-expanded tetracyanobutadiene (also known as expanded-TCBD or exTCBD), have been introduced into the triphenylamine-quinoxaline molecular framework using a catalyst-free [2 + 2] cycloaddition-retroelectrocyclization reaction.

Charge-Transfer in Panchromatic Porphyrin-Tetracyanobuta-1,3-Diene-Donor Conjugates: Switching the Role of Porphyrin in the Charge Separation Process.

Using a combination of cycloaddition-retroelectrocyclization reaction, free-base and zinc porphyrins (H P and ZnP) are decorated at their β-pyrrole positions with strong charge transfer complexes, viz., tetracyanobuta-1,3-diene (TCBD)-phenothiazine (3 and 4) or TCBD-aniline (7 and 8), novel class of push-pull systems. The physico-chemical properties of these compounds (MP-Donor and MP-TCBD-Donor) have been investigated using a range of electrochemical, spectroelectrochemical, DFT as well as steady-state and time-resolved spectroscopic techniques.

Push-Pull Porphyrins via β-Pyrrole Functionalization: Evidence of Excited State Events Leading to High-Potential Charge-Separated States.

A new set of free-base and zinc(II)-metallated, β-pyrrole-functionalized unsymmetrical push-pull porphyrins were designed and synthesized via β-mono- and dibrominated tetraphenylporphyrins using Sonogashira cross-coupling reactions. The ability of donors and acceptors on the push-pull porphyrins to produce high-potential charge separated states was investigated. The porphyrins were functionalized at the opposite β,β'-pyrrole positions of porphyrin ring bearing triphenylamine push groups and naphthalimide pull groups.