biostudies-literatureSoejima KIketani Science and Technology FoundationMinistry of Education, Culture, Sports, Science and TechnologyKumamoto UniversityJapan Society for the Promotion of Science35892-35898https://www.ebi.ac.uk/biostudies/studies/S-EPMC12477679biostudies-literatureUnknown15(43)Exploring new compounds that exhibit spin-state switching under external stimuli is crucial for advancing materials science. However, the feasibility of combining π-conjugated moieties with Co(ii)-terpy cation units via an ethynyl group has not yet been investigated. This approach represents a hybridization strategy wherein distinct functional moieties are incorporated into a single coordination metal complex to achieve multifunctionality. In this study, we synthesised a series of Co(ii)-terpyridine complexes [Co(R-ethynyl-terpy)2](BF4)2 (R = phenyl for 1, naphthyl for 2, anthracenyl for 3, and pyrenyl for 4), resolved their crystal structures and packing arrangements, and evaluated their magnetic properties using a superconducting quantum interference device magnetometer. These Co(ii)-based complexes exhibited thermal spin-crossover behaviour in the solid state. Although complexes 1-4 were luminescent in solution, only complexes 3 and 4 emitted dual monomer and excimer fluorescence in solution due to their substituted π-conjugated moieties. Our findings are expected to serve as a platform for the synthesis of magnetically functional coordination metal compounds based on Co(ii) ions for the potential development of photophysical materials.RSC advancesObservation of spin-crossover behaviour in Co(ii)-terpyridine complexes possessing π-conjugated substations.PMC12477679JP24K01502JPMXS0320200363JP24K08449Zenno HSoejima KMiyake KHayami SSekine YKiba KYamaguchi YfalseObservation of spin-crossover behaviour in Co(ii)-terpyridine complexes possessing π-conjugated substations.Exploring new compounds that exhibit spin-state switching under external stimuli is crucial for advancing materials science. However, the feasibility of combining π-conjugated moieties with Co(ii)-terpy cation units via an ethynyl group has not yet been investigated. This approach represents a hybridization strategy wherein distinct functional moieties are incorporated into a single coordination metal complex to achieve multifunctionality. In this study, we synthesised a series of Co(ii)-terpyridine complexes [Co(R-ethynyl-terpy)2](BF4)2 (R = phenyl for 1, naphthyl for 2, anthracenyl for 3, and pyrenyl for 4), resolved their crystal structures and packing arrangements, and evaluated their magnetic properties using a superconducting quantum interference device magnetometer. These Co(ii)-based complexes exhibited thermal spin-crossover behaviour in the solid state. Although complexes 1-4 were luminescent in solution, only complexes 3 and 4 emitted dual monomer and excimer fluorescence in solution due to their substituted π-conjugated moieties. Our findings are expected to serve as a platform for the synthesis of magnetically functional coordination metal compounds based on Co(ii) ions for the potential development of photophysical materials.2025-01-01T00:00:00Z2025 Sep2026-06-03T23:29:15.945Z2026-05-03T03:11:14.849ZS-EPMC124776794103030510.1039/d4ra08657k