Synthesis and Characterization of Pyrylogens Possessing Low Excitation Energies – Substituent Modification in Order to Improve Solar Energy Collection

Abstract The synthesis and characterization of the first di‐β‐naphthyl‐substituted pyrylogens, N ‐methyl‐2,6‐di‐β‐naphthyl‐4,4′‐pyrylogen bis(tetrafluoroborate) and N ‐methyl‐2,6‐di‐β‐naphthyl‐4,2′‐pyrylogen bis(tetrafluoroborate) are reported. The photophysical and electrochemical behaviors of these new pyrylogens are examined and compared to the previously reported diphenyl‐substituted analogs, N ‐methyl‐2,6‐diphenyl‐4,4′‐pyrylogen bis(tetrafluoroborate) and N ‐methyl‐2,6‐diphenyl‐4,2′‐pyrylogen bis(tetrafluoroborate) as well as to 2,4,6‐triphenylpyrylium tetrafluoroborate, the typical electron‐transfer photocatalyst. The newly synthesized pyrylogens exhibit substantially lower excitation energies. The results are supported by theoretical calculations using the B3LYP/6‐31G(d) and time‐dependent DFT (TD‐DFT) CAM‐B3LYP/6‐31G(d) computational models. In addition, insight into the reduction reactions of the new pyrylogens to their radical cation and neutral redox partners is also provided.