Fluorinated Distyrylbenzene Chromophores:  Effect of Fluorine Regiochemistry on Molecular Properties and Solid-State Organization

Abstract

A series of fluorinated distyrylbenzene (DSB) derivatives were synthesized and studied in order to probe the effect of fluorine substitution on molecular properties and on the arrangement of molecules in the solid state. Reaction of 1,4-diiodobenzene with 4-fluorostyrene or pentafluorostyrene in the presence of Pd(OAc)2 gives trans-trans-bis(4-fluorostyryl)benzene (2F t ) and trans- trans-1,4-bis(pentafluorostyryl)benzene (10F t ), respectively. Bis(2,5-difluorostyryl)benzene (4F t ) was prepared by the reaction of 2,5-difluorobenzaldehyde with p-xylylenebis-(triphenylphosphonium bromide) in the presence of LiOEt in EtOH. Coupling of 1,4-dibromo-2,5-difluorobenzene with styrene, 4-fluorostyrene, or pentafluorostyrene using Pd(OAc)2 gives 1,4-bis(styryl)-2,5-difluorobenzene (2F c ), 1,4-bis(4-fluorostyryl)-2,5-difluorobenzene (2F c 2F t ), and 1,4-bis(pentafluorostyryl)-2,5-difluorobenzene (2F c 10F t ), respectively. Absorption spectroscopy shows that DSB, 2F t , 2F c , 2F c 2F t , 4F t , 10F t , and 2F c 10F t have a λmax at approximately 350 nm. Addition of dimethylaniline to hexane solutions results in exciplex emission with λmax ranging from 458 to 514 nm, depending on fluorine regiochemistry. Cyclic voltammetry shows that, as the fluorine load increases, the reduction of the DSB framework becomes more facile. It is also shown that the regiochemistry of substitution makes an impact on the inductive ability of fluorine to facilitate reduction. The lattice properties of 2F c , 2F c 2F t , 4F t , 10F t , and 2F c 10F t were determined by X-ray diffraction experiments. Two structural motifs emerge from these studies. One is the tendency of the DSB framework to stack cofacially and form vertical “columns” within the crystal. The second motif is the alignment of these “columns” to maximize C−H···F electrostatic registry.

Optical Bandgaps of π‐Conjugated Organic Materials at the Polymer Limit: Experiment and Theory

“…This shift is triggered by the mesomeric (±M, with + and -indicating a donor and acceptor effect, respectively) and/or inductive (±I) effects associated with the substituents, leading to an asymmetric (de)-stabilization of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels. A striking exception is substitution with fluorine atoms, in which case the subtle balance between the M and -I effects leads to either a blue-or red-shift, depending on the number and position of the substituents [75] as well the nature of the molecular backbone. [75][76][77] A red-shift of the adiabatic transition energy upon substitution does not necessarily imply a red-shift of the vertical transition energy and of the absorption maximum (A max ), because the latter are also influenced by the shape of the torsional potential in the electronic ground state.…”

Pd-Catalyzed Mizoroki-Heck Reactions Using Fluorine-Containing Agents as the Cross-Coupling Partners

“…Gladysz and co-workers reported a convenient and scalable procedure for the cross-couplings of fluorous alkenes (80) with aryl bromides (81) using a modified Jeffery version of the MizorokiHeck reaction (Scheme 16) [72]. Fluorous alkenes (80) reacted with aryl monobromides and polybromides (81), such as 1,3-and 1,4-C6H4Br2, 1,3,5-C6H3Br3, 1,3,5-C6H3Br2Cl, 1,4-XC6H4Br (X = CF3, C8F17, COCH3, CN, 1,4-OC6H4Br), 1,2-O2NC6H4Br, 5-bromo-isoquinoline, 5-bromopyrimidine, 3-bromo-5-methoxypyridine, and 3,5-dibromopyridine, under the modified Mizoroki-Heck coupling conditions to afford the corresponding fluorophilic adducts (82) in good to high yields. Typically, 1.2-2.4 equiv.…”

“…A series of fluorinated distyrylbenzene (DSB) derivatives (124 and 126) were synthesized by Pdcatalyzed Mizoroki-Heck cross-couplings (Scheme 24) [81]. The reaction of 1,4-diiodobenzene (122a) with pentafluorostyrene (123) or 4-fluorostyrene (125b) in the presence of Pd(OAc)2 gave trans-trans-1,4-bis(pentafluorostyryl)benzene (124a) or trans-trans-bis(4-fluorostyryl)benzene (126a).…”

“…The coupling of 1,4-dibromo-2,5-difluorobenzene (122b) with styrene (125a), 4-fluorostyrene (125b), or pentafluorostyrene (123) using Pd(OAc)2 provided 1,4-bis(styryl)-2,5-difluorobenzene (126b), 1,4-bis(4-fluorostyryl)-2,5-difluorobenzene (126c), and 1,4-bis-(pentafluorostyryl)-2,5-difluorobenzene (124b), respectively. The products were employed to probe the effect of fluorine substitution on the molecular properties and on the arrangement of molecules in the solid state [81]. The absorption spectroscopy showed that 124 and 126 had a λmax at approximately 350 nm, and addition of dimethylaniline to the hexane solutions led to exciplex emission with λmax ranging from 458 to 514 Furthermore, Pd-catalyzed Heck-type cyclization of 2-trifluoromethyl-1-alkenes (118) bearing an O-acyloxime moiety was accomplished (Scheme 23) [45,80].…”

Structural motifs in acetoacetanilides: the effect of a fluorine substituent

“…The presence of¯uorine in molecular crystals and its in¯uence on crystal packing have been comparatively rarely studied [for examples, see Hayashi & Mori (1998) and Renak et al (1999)], given the wealth of information available on the effect of the F atom in biological chemistry (Filler et al, 1993). The interactions of organic¯uorine with other atoms within a crystal lattice are weak and, indeed, it has been observed that, when organically bonded,¯uorine hardly ever acts as a hydrogen-bond acceptor (Dunitz & Taylor, 1997).…”