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Tuning Structural and Electronic Communication through Metal Coordination in Axially Bonded 3-Pyrrolyl
Debendra Tewary1,2, Abani Sarkar1, David R Turner2
1Department of Chemistry, IIT Bombay, Powai, 400076 Mumbai, India.
None:
Axially coordinated multichromophoric assemblies provide an effective platform for modulating electronic communication through metal-ligand interactions. Herein, we report the synthesis and comprehensive structural, photophysical, electrochemical, and computational investigation of four axially bonded 3-pyrrolyl BODIPY-metalloporphyrin conjugates comprising two Zn(II) porphyrin dyads and two Sn(IV) porphyrin triads. X-ray analysis of the Zn(II) dyads reveals distinct tilted and nearly orthogonal BODIPY-porphyrin geometries. The dyads show partial fluorescence quenching, which, together with a favorable spectral overlap, an excited-state lifetime of τ ≈ 1.63 ns, and uphill electron transfer (ΔG ≈ +0.18 eV), supports a Förster resonance energy transfer pathway. In contrast, the Sn(IV) triads exhibit ultrafast fluorescence quenching (τ ≈ 0.49 ns) and thermodynamically favorable charge separation (ΔG ≈ -0.16 eV). Triads show complementary EPR evidence under dark conditions consistent with a charge-separated intermediate, supporting photoinduced electron transfer. Electrochemical studies show distinct redox processes for the dyads, whereas the triads display broadened reduction features indicative of enhanced electron and charge delocalization. DFT calculations show a systematic decrease in the HOMO-LUMO gap from 2.34 to 1.14 eV. These results establish clear structure property relationships governing energy and electron transfer processes in axially coordinated 3-pyrrolyl BODIPY-metalloporphyrin assemblies.
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