Insight into structure-property relationships of aryl-substituted 2,2′:6′,2″-terpyridines

Abstract A series of 2,2′:6′,2″-terpyridines functionalized with polyaromatic groups have been synthesized and their optical properties have been examined in detail, with the support of theoretical calculations at DFT/TD-DFT level. The investigated molecules show twisted ground state conformations with the twist angle impacted by steric hindrance due to the inter-ring H⋯H repulsions. The largest steric hindrance effect (77.3°) was found for 4′-(anthracen-9-yl)-2,2′:6′,2″-terpyridine, while replacement of 1-naphtyl, 9-anthryl and 1-pyrenyl with appropriate 2-naphtyl, 2-anthryl and 2-triphenylenyl results in the decrease in dihedral angle between the plane of polyaromatic group and central pyridine ring. The longest wavelength absorption band of anthryl-, pyrenyl- and perylenyl-substituted terpyridines is predominately contributed by the aryl unit, while low-energy absorptions of other Ar-terpys are assigned to both π−π*(terpy) and π−π*(aryl) transitions. For 4′-(pyren-1-yl)-2,2′:6′,2″-terpyridine and 4′-(perylen-3-yl)-2,2′:6′,2″-terpyridine, the UV–Vis spectra support relatively strong interaction between the chromophoric moieties of Ar-terpys in the ground state. In the excited singlet state, intramolecular charge transfer (ICT) transitions originating from charge delocalization from the aryl unit to terpy acceptor moiety has been evidenced for 4′-(anthracen-2-yl)-2,2′:6′,2″-terpyridine, 4′-(pyren-1-yl)-2,2′:6′,2″-terpyridine and 4′-(perylen-3-yl)-2,2′:6′,2″-terpyridine.