Luminescent Zr Complexes with Long-lived Intraligand Charge Transfer Excited States

Journal Article · Tue Jan 06 00:00:00 EST 2026 · ChemRxiv

DOI:https://doi.org/10.26434/chemrxiv-2026-gprqp· OSTI ID:3012422

Nattikallungal, Thabassum A. ^[1]; Shariaty, Darius A. ^[1]; Lien, Yi-Jyun ^[1]; Gonzales, Chloe ^[1]; Djurovich, Peter I. ^[1]; Bradforth, Stephen E. ^[1]; Thompson, Mark E. ^[1]

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1. University of Southern California

Understanding and establishing design principles to tune the excited states of earth-abundant sensitizers is crucial for identifying new photosensitizers for sustainable technological advancements. Here, we report a series of three bis Zr (IV) complexes of tridentate, dianionic ligands incorporating two phenoxide donors and aza arene acceptors of increasing electron affinity (pyridine < pyrimidine < pyrazine ) that are air and water-stable. These complexes emit via thermally assisted delayed fluorescence from an intraligand charge transfer excited state with varying metal contributions. The electronic structural changes from different acceptors vary the excited state character and the photophysical properties significantly between the complexes. The variation in photophysics that includes emission lifetime (76 μs to 265 ns), intersystem crossing (ISC) lifetime ( 390 – 290 ps), and the energy difference between the singlet and triplet excited states (∆EST. 170 -100 meV). We observe solvent-independent ISC rates when the excited state has metal contributions (acceptor = pyridine), and the ISC rates vary significantly with solvent polarity when the excited state is an intra-ligand charge transfer state (acceptor = pyrimidine and pyrazine). Transient absorption measurements provided the basis spectra and verified the metal contribution in the excited state. This work provides a basis for developing new sensitizers based on Zr (IV) by providing design principles that can be used to modulate the character of the excited state and its photophysics.

• Research Organization: University of Southern California
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division (CSGB)
• Grant/Contract Number: SC0016450
• OSTI ID: 3012422
• Journal Information: ChemRxiv, Journal Name: ChemRxiv
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English