Synthesis and Light‐Harvesting Potential of Cyanovinyl β‐Substituted Porphyrins and Dyads

Abstract

Knoevenagel condensation has been utilized as an alternative way to synthesize a series of β‐vinyl‐substituted porphyrins and porphyrin dyads with good to excellent yields. The condensation of β‐formyl porphyrins and phenylacetonitriles allows control of the substitution pattern and metal centres in the porphyrin dyads, allowing the use of metallated synthons. While the optical and electronic properties of the resulting porphyrin dyes are perturbed by the presence of the cyano substituent, this does not significantly affect their use. For example, Raman spectroscopy, in agreement with density functional theory (DFT) and time‐dependent DFT (TD‐DFT) calculations, show porphyrin electronic transitions with delocalization of frontier molecular orbital electron density onto the β substituent. A comparison of the photovoltaic performance of a carboxylated cyanostyryl condensation product and the unsubstituted analogue in dye‐sensitized solar cells (DSSCs) was made. Although the devices showed similar efficiency, the device containing the cyano‐substituted dye showed an extended incident photon‐to‐current conversion efficiency (IPCE) due to a slight red‐shift in absorption and an increase in photovoltage as a result of a longer electron lifetime. This minimal change in light‐harvesting performance highlights the potential of this Knoevenagel synthetic methodology for producing light‐harvesting porphyrin dyes.

Modulation of Donor-Acceptor Distance in a Series of Carbazole Push-Pull Dyes; A Spectroscopic and Computational Study

“…To further probe the observed electronic transitions and attempt to better understand how the implemented structural changes result in the observed optical changes, resonance Raman spectroscopy (RRS) was carried out at a number of excitation wavelengths across the absorption bands of the compounds. Resonance Raman spectroscopy shows band enhancements for modes that are associated with the resonant chromophore [ 16 , 20 , 41 , 50 , 51 ], thus it is possible to provide experimental evidence for the nature of the observed chromophores to support the calculated electronic transitions data.…”

“…To facilitate a more complete exploration of the electronic structure and optical properties two functionals were used in the calculations; namely B3LYP and CAM-B3LYP. The second of these contains a range correction which has been shown to be effective at modeling charge transfer in systems [ 15 , 16 , 41 ].…”

New nitroindazole-porphyrin conjugates: Synthesis, characterization and antibacterial properties

“…The authors mentioned that the reactions with phenylacetonitriles bearing strong electron-donating groups need to be mediated with strong bases, such as 1,8diazabicyclo [5.4.0]undec-7-ene (DBU) or KOtBu. The authors explored this approach to prepare symmetrical and unsymmetrical porphyrin dyads by using 1,4-phenylenediacetonitrile, in the presence of DBU or sodium methoxide [44].…”