The Effect of Torsional Motion on Multiexciton Formation through Intramolecular Singlet Fission in Ferrocene-Bridged Pentacene Dimers.

A series of ferrocene(Fc)-bridged pentacene(Pc)-dimers [Fc-Ph(2,n)-(Pc) ₂ : n=number of phenylene spacers] were synthesized to examine the tortional motion effect of Fc-terminated phenylene linkers on strongly coupled quintet multiexciton ( ⁵ TT) formation through intramolecular singlet fission (ISF). Fc-Ph(2,4)-(Pc) ₂ has a relatively small electronic coupling and large conformational flexibility according to spectroscopic and theoretical analyses. Fc-Ph(2,4)-(Pc) ₂ exhibits a high-yield ⁵ TT together with quantitative singlet TT ( ¹ TT) generation through ISF. This demonstrates a much more efficient ISF than those of other less flexible Pc dimers. The activation entropy in ¹ TT spin conversion of Fc-Ph(2,4)-(Pc) ₂ is larger than those of the other systems due to the larger conformational flexibility associated with the torsional motion of the linkers. The torsional motion of linkers in ¹ TT is attributable to weakened metal-ligand bonding in the Fc due to hybridization of the hole level of Pc to Fc in ¹ TT unpaired orbitals.
(© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)