Synthesis, structural characterization and fluorescence enhancement of chromophore‐modified polyoxometalates

• Published in: Acta crystallographica. Section C, Crystal structure communications Crystal structure communications, 2018-11, Vol.74 (11), p.1260-1266
• Main Authors: Fura, Gizaw D., Long, Yong, Yan, Jun, Chen, Wei, Lin, Chang-Gen, Song, Yu-Fei
• Format: Article
• Language: English
• Subjects: Anderson cluster; Charge transfer; Chemical synthesis; chromophore; Chromophores; crystal structure; Emission analysis; Fluorescence; Hybrids; organic–inorganic hybrid; polyoxometalate; Polyoxometallates; POM; Quenching; Structural analysis; Tethering; X ray spectra; X-ray diffraction
• ISSN: 2053-2296; 0108-2701; 2053-2296; 1600-5759
• DOI: 10.1107/S2053229618009361

Intramolecular charge transfers between π‐conjugated molecules and polyoxometalate (POM) clusters have been observed in donor–acceptor systems based on organic donors and inorganic POM acceptors, which unfortunately results in a general quenching of the chromophore luminescence. The development of POM–chromophore dyads that are capable of tackling the quenching process and enhancing the fluorescence intensity of such systems remains a highly challenging area of study. A family of organic–inorganic polyoxometalate hybrids, {[(n‐C4H9)4N]3[(MnMo6O24){(CH2)3CR}2]} [1, R = –NHCH2C14H9, namely (anthracen‐9‐ylmethyl)amino; 2, R = –NHCH2C13H9, (9H‐fluoren‐2‐ylmethyl)amino; 3, R = –NHCH2C10H7, (naphthalen‐2‐ylmethyl)amino; 4, R = –NHCH2C16H9, (pyren‐2‐ylmethyl)amino], were synthesized by covalently tethering π‐conjugated molecules onto an Anderson cluster. The resulting POM–chromophore dyads were fully characterized by various spectroscopic techniques, single‐crystal X‐ray diffraction analysis and ESI–MS. The fluorescence features of these dyads were studied in detail to verify a dramatic emission enhancement that can be achieved by fine‐tuning the microenvironment in solution and suppressing the intrinsic photo‐induced electron‐transfer process. Three new chromophore‐modified polyoxometalates have been synthesized and characterized by single‐crystal X‐ray diffraction. The fluorescence properties of the resulting polyoxometalate hybrids can be boosted by tuning the solvents. We demonstrate an easy and feasible method for solving the fluorescence quenching problem of POM–chromophore dyads. Our work may open up a new pathway for the development of POM‐based fluorescent sensors or switches.