title: Fine-Tuning of β-Substitution to Modulate the Lowest Triplet Excited States: A Bioinspired Approach to Design Phosphorescent Metalloporphyrinoids.
abstract: Learning nature's approach to modulate photophysical properties of NIR porphyrinoids by fine-tuning β-substituents including the number and position, in a manner similar to naturally occurring chlorophylls, has the potential to circumvent the disadvantages of traditional "extended π-conjugation" strategy such as stability, molecular size, solubility, and undesirable π-π stacking. Here we show that such subtle structural changes in Pt(II) or Pd(II) cis/trans-porphodilactones (termed by cis/trans-Pt/Pd) influence photophysical properties of the lowest triplet excited states including phosphorescence, Stokes shifts, and even photosensitization ability in triplet-triplet annihilation reactions with rubrene. Prominently, the overall upconversion capability (η, η = ε·Φ(UC)) of Pd or Pt trans-complex is 10(4) times higher than that of cis-analogue. Nanosecond time-resolved infrared (TR-IR) spectroscopy experiments showed larger frequency shift of ν(C═O) bands (ca. 10 cm(-1)) of cis-complexes than those of trans-complexes in the triplet excited states. These spectral features, combining with TD-DFT calculations, suggest the strong electronic coupling between the lactone moieties and the main porphyrin chromophores and thus the importance of precisely positioning β-substituents by mimicking chlorophylls, as an alternative to "extended π-conjugation", in designing NIR active porphyrinoids.
authors.affiliation: Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University , Beijing 100871, P.R. China.
authors.forename: Xian-Sheng
authors.initials: XS
authors.lastname: Ke
authors.affiliation: Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, P.R. China.
authors.forename: Hongmei
authors.initials: H
authors.lastname: Zhao
authors.affiliation: Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, P.R. China.
authors.forename: Xiaoran
authors.initials: X
authors.lastname: Zou
authors.affiliation: Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University , Beijing 100871, P.R. China.
authors.forename: Yingying
authors.initials: Y
authors.lastname: Ning
authors.affiliation: Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University , Beijing 100871, P.R. China.
authors.forename: Xin
authors.initials: X
authors.lastname: Cheng
authors.affiliation: Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, P.R. China.|College of Chemistry, Beijing Normal University , Beijing 100875, P.R.China.
authors.forename: Hongmei
authors.initials: H
authors.lastname: Su
authors.affiliation: Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University , Beijing 100871, P.R. China.|State Key Laboratory of Coordination Chemistry, Nanjing University , Nanjing, 210093, P.R. China.
authors.forename: Jun-Long
authors.initials: JL
authors.lastname: Zhang
mesh_terms: D032701:Biomimetics / Q000379:methods*; D015195:Drug Design; D049408:Luminescent Agents / Q000737:chemistry*; D008665:Metalloporphyrins / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D010165:Palladium / Q000737:chemistry; D017319:Photosensitizing Agents / Q000737:chemistry; D010984:Platinum / Q000737:chemistry; D013237:Stereoisomerism
chemical_list: D049408:Luminescent Agents; D008665:Metalloporphyrins; D017319:Photosensitizing Agents; D010984:Platinum; D010165:Palladium