Revisiting indeno[1,2-b]fluorene by steric promoted synthesis while isolating the second stable 4nπ indeno[2,1-a]fluorene

Abstract

Described herein are the steric promoted synthesis and characterization of symmetric, unsymmetric, and benzo-extended indeno[1,2-b]fluorenes 1-5, including isolation of a stable 4nπ indeno[2,1-a]fluorene 6. Single-crystal XRD analyses of 5 and...

Exploring Indeno[2,1-c]fluorene Antiaromatics with Unsymmetrical Disubstitution and Balanced Ambipolar Charge-Transport Properties

“…Our report of convenient access to fully conjugated [2,1-c]IFs bearing desired substituents with balanced ambipolar charge-transport properties for 1, 7, 8 and 17 in the order of 10 −3 cm 2 V −1 s −1 could open the gateway to previously inaccessible apically extended antiaromatic materials for diverse applications in organic optoelectronics devices. To the best of our knowledge, this is the first systematic study of charge-carrier mobility of antiaromatic [2,1-c]IFs bearing symmetrical (1,17) and unsymmetrical (7) disubstitution comprising two particular substituents (mesityl and C6F5). Our work distinctly showed the potential of [2,1-c]IF scaffolds as efficient charge-transporting materials, one of the fundamental requirements for efficient organic electronic devices, which is in contrast to earlier prediction.…”

“…1 Mesityl group is found to be near orthogonally oriented to the [2,1c]IF backbone (dihedral angle 86.9°-89.7° for 7 and 9), while the other aryl/ethynyl groups suggest better π-delocalization trend on moving from C6F5 in 7 (a reduced dihedral angle ~ 52.6°) to TIPSE in 9 (co-planar). The bond-lengths of the [2,1-c]IF backbones clearly suggested a para-quinoidal arrangement of the as-indacene 1,7,8 (C=C double bond distances are shown in Figure 2a, 2b and 2c) for all the derivatives, including homogeneous Csp 2 -Csp 2 bond length distributions in the outer benzenoid rings for 7, 9, and 17, which clearly imply benzene aromaticity for outer six-membered rings. 1,7 X-ray crystallographic analysis of 7 has shown several close contacts in the solid-state (Figure S39) with intermolecular non-covalent interactions between C(9)-C( 5 2)⋯H(34)-Csp 2 hydrogen bonding interaction measuring 2.457 Å (the value is less than the sum of the van der Waals radii of F and H = 2.67 Å) 17 with ∠Csp 2 -H•••F = 137.8°, affording a herringbone-like packing arrangement (Figure S39) with an one-dimensional columnar stack featuring the C6F5 unit partly, cofacially, π-stacking (3.238 Å) with the outer ring of IF (Figure 2d).…”

“…Template for Organic Materials Thieme Unlike our steric approach to synthesize [1,2-b]IF that required mesityl as a bulky substituent, 7 current approach can be used to attach less bulky donors (like: 4-methoxyphenyl) to afford push-pull dyes. Compound 10 was synthesized using the analogous synthesis approach (Scheme 3) that started with a nucleophilic addition of (4-methoxyphenyl)magnesium bromide to aldehyde 11 to afford 25.…”

“…mp: 115-116 °C. (7). DDQ (34 mg, 0.14 mmol, 2 equiv) was added to degassed solution of precursor 20 (40 mg, 0.07 mmol) in toluene (2 mL), and the reaction mixture was heated to 100 °C for 2 h. The progress of the reaction was monitored by TLC and stopped after 2 h, followed by purification by silica gel column chromatography (hexanes) to afford the final compound 7 as green solid (31 mg, 78 % yield).…”

“…Lately, two unsymmetrically disubstituted IF regioisomers were reported by us with tunable antiaromaticity. 7 We had reported a new synthesis approach to 1, 8 and further to a (4 n + 2)π s-indacenodifluorene. Inspired by the general route for unsymmetrically 6,13disubstituted pentacene molecules for various applications 9 and considering appreciable molecular orbital density at the apical carbons of 1 (Figure 1c) or related as-indacene 10 that suggested possibility to tune the electronic properties of [2,1-c]IFs by apical elongation, including the non-availability of unsymmetrically 5,8-disubstituted [2,1-c]IFs, we envisaged to extend our synthetic approach 8 as a general route to access the yet inaccessible unsymmetrically 5,8-disubstituted [2,1-c]IF scaffolds 7, 8, 9 and 10 (Figure 1d), and a previously unknown 1 symmetrically disubstituted [2,1-c]IF 17.…”