To study the photophysical and redox properties as a function of meso-aryl units, a series of hypervalent phosphorus(V) porphyrins, PP(OMe)2·PF6, PMP(OMe)2·PF6, PDMP(OMe)2·PF6, P345TMP(OMe)2·PF6, and P246TMP(OMe)2·PF6, with phenyl (P), 4-methoxyphenyl (MP), 3,5-dimethoxyphenyl (DMP), 3,4,5-trimethoxyphenyl (345TMP), and 2,4,6-trimethoxyphenyl (246TMP) units, respectively, have been synthesized. The P(+5) in the cavity makes the porphyrin ring electron-poor, whereas the methoxy groups make the meso-phenyl rings electron-rich. The presence of electron-rich and electron-poor portions within the porphyrin molecule promoted an intramolecular charge transfer (ICT). Also, the study suggests that the ICT depends on the number and position of the methoxy groups. The ICT is more prominent in m-methoxy-substituted phosphorus(V) porphyrins (PDMP(OMe)2.PF6, P345TMP(OMe)2·PF6) and almost no ICT was found in no-methoxy, o-methoxy, and/or p-methoxy phosphorus(V) porphyrins (PP(OMe)2·PF6, PMP(OMe)2·PF6, P246TMP(OMe)2·PF6). Transient absorption studies indicate that the ICT takes place on the picosecond time scale. The most striking results come from P246TMP(OMe)2·PF6, where each phenyl ring carries three methoxy units, like the P345TMP(OMe)2·PF6, but it failed to induce the ICT process. Electrochemical studies and time-dependent density functional theory (TD-DFT) calculations were used to support the experimental results. This study extensively explores why and how slight variations in meso-aryl substitutions lead to intricate changes in the photophysical and redox properties of phosphorus(V) porphyrins.
Bibliographical noteFunding Information:
This work was supported by the Grant-in-Aid program (No. 380228) and the Advanced Materials Center─SEED Grant program, University of Minnesota Duluth, to P.P.K. and by the National Science Foundation (2000988 to F.D.). The authors also acknowledge the NSF-MRI Program (CHE-1726652), and the University of North Texas for supporting the acquisition of the Rigaku XtaLAB Synergy-S X-ray diffractometer. The computational work was completed at the Holland Computing Center of the University of Nebraska, which receives support from the Nebraska Research Initiative.
© 2022 American Chemical Society.