Optimizing the Catalytic Performance of Amine-Functionalized 4CzIPN Derivatives by Investigation of the Twisted Intramolecular Charge Transfer Effect

Amine-functionalized 4CzIPN derivatives exhibit extraordinary redox potentials in their excited state but are still often found to be ineffective in catalytic transformations. A possible reason for this disadvantage is the twisted intramolecular charge transfer (TICT) effect, which is known to affect the photophysical properties and thus the catalytic efficiency of such dyes. We have designed four amine-bearing triazole-linked 4CzIPN derivatives based on structural motifs that are known to enhance or suppress the transition into the TICT state through stereoelectronic properties in order to better understand and overcome the limitations possibly caused by this phenomenon. By applying these derivatives in challenging oxidative and reductive transformations, such as the bromination of anisole or the reductive dechlorination of methyl 4-chlorobenzoate, we demonstrated that some of the new compounds are more powerful catalysts than 4CzIPN. This seems to indicate that considerations about the TICT effect are a powerful tool for harnessing the outstanding redox powers of amine-functionalized organic photocatalysts in organic synthesis. However, quantum chemical investigations yield detailed insights into the photoelectronic features of the dyes, which modify the assumptions to some extent.