Dibenzo[a,e]pentalenes with Low-Lying LUMO Energy Levels as Potential n-Type Materials

Abstract

Ambipolar organic semiconductors are of high interest for organic field-effect transistors. For n-type conduction, low LUMO energies are required. Dibenzo[a,e]pentalenes (DBPs) are promising compounds; however, few derivatives exist with energetically low-lying LUMO levels. Here, we present DBP derivatives with LUMO energies down to -3.73 eV and small bandgaps down to 1.63 eV determined through cyclic voltammetry, UV/vis absorption spectroscopy, and TDDFT calculations. Single-crystal X-ray diffraction analysis revealed a 1D π-stacking mode. The addition of arylalkynyl substituents at the five-membered rings in a facile and versatile synthetic route allowed for tuning of the band gaps and LUMO energies. The synthetic route can easily be modified to access a variety of DBP derivatives. The LUMO energies of the DBP derivatives presented herein make them attractive for an application in n-type or ambipolar field-effect transistors.

Dibenzo[a,e]pentalenophanes: Bending a Non‐Alternant Hydrocarbon

“…The longest wavelength absorption bands, assigned to the HOMO→LUMO transitions, had maxima at 503 nm for DBP‐phanes 1 [ n ] and 490 nm for 7 (Figure , inset). The low extinction coefficients of this transition can be explained by its forbidden nature for planar and centrosymmetric DBP derivatives, where both orbitals are of a u symmetry (Laporte's rule) . Even though the symmetry is broken in cyclic DBP‐phanes 1 [ n ], the calculated oscillator strengths for the HOMO→LUMO transitions lay below 0.016 (see the Supporting Information).…”

“…None of the DBP‐phanes 1 [ n ] nor model compound 7 showed fluorescence. This is known for DBP derivatives and for the structurally related indeno[1,2‐ b ]fluorenes, where transient absorption spectroscopy measurements showed that the excited state lifetimes were shorter than the timescale at which fluorescence is usually observed …”

“…The 3,5‐bis(trifluoromethyl)phenyl‐substituents facilitated reduction by Δ E =+0.50 V relative to 7 , but exhibited a smaller effect on the oxidation (Δ E =+0.19 V). We have observed the same trend in other DBP derivatives, where substituents in the 5,10‐positions have a stronger influence on the LUMO energy and 2,7‐substituents on the HOMO energy . In DBP‐phane 12 [ 12 ], reduction was likewise facilitated by Δ E =+0.51 V compared with mesityl‐substituted 1 [ 12 ], whereas the oxidation was shifted to higher potential by only Δ E =+0.18 V. The second oxidation process was irreversible as had been the case for 1 [ 12 ].…”

Gold‐Catalyzed Facile Synthesis and Crystal Structures of Benzene‐/Naphthalene‐Based Bispentalenes as Organic Semiconductors

“…Due to the promising properties of π‐extended pentalenes they are attractive as organic semiconductors. Dinaphto[ a , e ]pentalene, dianthraceno[ a , e ]pentalene and the pyrrole‐fused dibenzo[ a , e ]pentalene exhibit high hole mobilities, while the thiophene‐substitued dibenzo[ a , e ]pentalenes and diacenopentalene dicarboximides exhibit lower‐lying LUMO levels suitable for n‐type semiconductors . Despite the development of π‐extended pentalenes, the synthesis of bispentalenes is not yet well studied .…”

N‐Heterocycle‐Fused Pentalenes by a Gold‐Catalyzed Annulation of Diethynyl‐Quinoxalines and ‐Phenazines

“…For instance, a palladium‐/rhodium‐catalyzed intermolecular annulation of alkynes, a B(C 6 F 5 ) 3 ‐mediated cyclization of 1,2‐diethynylbenzenes and anionic or radical anionic trans ‐annulations . The development of synthetic methods towards dibenzo[a,e]pentalenes has been accompanied by studies focusing on their properties and potential application . The optical and electrochemical properties of dibenzo[a,e]pentalenes are typically tuned by functional groups on the fifth and tenth position and on the benzene rings.…”