9‑Phenanthrenylvinyl-4′-pyridine\nand\nIts <i>N</i>‑Methylated Analogue: From the Crystal\nStructure and Photoisomerization to Photophysical and Electrochemical\nProperties and Application in Bioimaging

Designing novel functional compounds is a key step in\ncoordination\nand organic materials chemistry. Herein, 9-phenanthrenylvinyl-4′-pyridine\n(<b>9-PheVP</b>), as a new ligand, has been synthesized and\nstructurally characterized for the first time, along with its <i>N</i>-methylated analogue (<b>9-MPheVP</b>). Both compounds\nhave been explored for their photophysical and redox properties and\ntheir applicability in bioimaging. The effect of quaternization on\nthe crystal structure, absorption, emission, and redox properties\nhas been investigated. Bathochromic and hypochromic shifts were observed\nin the absorption and emission properties upon quaternization. Both\nneutral and cationic compounds showed large Stokes shifts of 9250\nand 8000 cm<sup>–1</sup>, respectively. <b>9-MPheVP</b> was observed to photoisomerize in the solid state to its <i>cis</i>-configuration (<b>9-MPheVP-</b><i>cis</i>) upon exposure to light. Crystal structure determination of <b>9-MPheVP-</b><i>cis</i> revealed that with <i>Z</i>′ = 2, it represents a rare class of crystals for which <i>Z′</i> > 1. The utility of <b>9-MPheVP</b> as\nan\nefficient ligand has also been established by structurally characterizing\na silver(I) complex, <b>[Ag(9-PheVP)</b><sub><b>2</b></sub><b>]BF</b><sub><b>4</b></sub>. Our results show that <b>9-PheVP</b> can serve as a promising ligand in coordination chemistry\nand offers a platform for developing multifunctional organic materials.