Structure–Property Relationships in an Iridium(III) Bis(Terpyridine) Complex with Extended Conjugated Side chains

Iridium(III) bis(terpyridine) complexes are known as excellent triplet emitters with emission lifetimes in the order of microseconds. We report the homoleptic complex [IrL2](3+) (L = 4'-(4-2,5-bis(octyloxy)-4-styrylphenyl)ethinyl)phenyl)-2,2':6',2″-terpyridine) that shows no detectable phosphorescence at room temperature but shows fluorescence. Emission spectra of [IrL2](3+) depend on the excitation wavelength. The origin of this behavior is studied with the help of results from (TD-)DFT calculations and is attributed to the selective excitation of different rotamers and isomers. Femtosecond-transient absorption experiments give further support for this interpretation as the specific excited-state absorption features of Z- and E-stilbene motives can be identified.