Angular ladder-typemeta-phenylenes: synthesis and electronic structural analysis

Herein, we report the synthesis of two new series of angular (all-syn) ladder-typemeta-[n]phenylenes (LMP,n= 3-8). One series contains keto groups at the termini bridges, denoted angular keto (AKn), the second contains alkyl groups at all bridge sp(3)carbons, denoted angular alkyl (AAn). Their electronic and structural properties were delineated by a combination of electrochemistry and spectroscopic (UV-Vis and emission) methods and further supported by DFT calculations. Interestingly, experimental and DFT data show that changing the bridging group at the termini from alkyl (AAn) to keto (AKn) gives an increase in the first reduction potentials and LUMO energies, as the pi-system is extended. Also, the charge (de)localization behavior is different for these two species; while the AAncompounds stablize charge with Robin-Day class III, the AKncompounds show a clear switch from class III to class II. In comparison with the linear analogues (LKnand LAn), DFT results reveal a shape independency of the charge (de)localization mechanism in acceptor-pi-acceptor series (AKn/LKn).