1,2-Bis[5-(2,2′-dicyano­vinyl)-2-n-pentyl-3-thien­yl]-3,3,4,4,5,5-hexa­fluoro­cyclo­pent-1-ene: a new photochromic diaryl­ethene compound

Min Li; Shou-Zhi Pu; Cong-Bin Fan; Zhang-Gao Le

doi:10.1107/S160053680800202X

. 2008 Jan 25;64(Pt 2):o517. doi: 10.1107/S160053680800202X

1,2-Bis[5-(2,2′-dicyanovinyl)-2-n-pentyl-3-thienyl]-3,3,4,4,5,5-hexafluorocyclopent-1-ene: a new photochromic diarylethene compound

Min Li ^a,^b, Shou-Zhi Pu ^b,^*, Cong-Bin Fan ^b, Zhang-Gao Le ^a

PMCID: PMC2960348 PMID: 21201536

Abstract

The title compound, C₃₁H₂₆F₆N₄S₂, is a new photochromic dithienylethene with dicyanovinyl subsitituents. In the crystal structure, the molecule adopts a photoactive antiparallel conformation, with two n-pentyl groups located on opposite sides of the cyclopentene ring. The cyclopentene ring assumes an envelope conformation. The distance between the two reactive C atoms on the thiophene rings is 3.834 (7) Å. One of the n-pentyl groups is disordered over two positions; the site occupancy factors are ca 0.7 and 0.3.

Related literature

For general background, see: Gilat et al. (1993 ▶, 1995 ▶); Irie (2000 ▶); Pu et al. (2003 ▶, 2005 ▶); Tian & Yang (2004 ▶); Yamaguchi & Irie (2006 ▶); Zheng et al. (2007 ▶). For related structures, see: Kobatake et al. (2004 ▶); Woodward & Hoffmann (1970 ▶).

Experimental

Crystal data

C₃₁H₂₆F₆N₄S₂
M _r = 632.68
Triclinic,
a = 9.2500 (12) Å
b = 12.3670 (16) Å
c = 15.596 (2) Å
α = 67.730 (2)°
β = 85.482 (2)°
γ = 72.804 (2)°
V = 1576.1 (4) Å³
Z = 2
Mo Kα radiation
μ = 0.23 mm⁻¹
T = 291 (2) K
0.29 × 0.21 × 0.16 mm

Data collection

Bruker SMART APEXII CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 1996 ▶) T _min = 0.932, T _max = 0.963
12153 measured reflections
5828 independent reflections
3782 reflections with I > 2s˘I)
R _int = 0.026

Refinement

R[F ² > 2σ(F ²)] = 0.049
wR(F ²) = 0.142
S = 1.03
5828 reflections
384 parameters
14 restraints
H-atom parameters constrained
Δρ_max = 0.41 e Å⁻³
Δρ_min = −0.26 e Å⁻³

Data collection: APEX2 (Bruker, 2004 ▶); cell refinement: SAINT (Bruker, 1997 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S160053680800202X/xu2397sup1.cif

e-64-0o517-sup1.cif^{(29.5KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S160053680800202X/xu2397Isup2.hkl

e-64-0o517-Isup2.hkl^{(285.3KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Acknowledgments

This work was financially supported by the fund of the Key Laboratory of Nuclear Resources and Environment, East China Institute of Technology, Ministry of Education, China (No. 060607).

supplementary crystallographic information

Comment

Photochromism has attracted considerable attention because of its potential application to photonic devices, such as optical memories and optical switches (Yamaguchi & Irie, 2006). Among various types of photochromic compounds, diarylethenes bearing two thiophene-derived groups have received the most attention because of their excellent fatigue resistant and outstanding thermally irreversible photochromic performance (Irie, 2000; Tian & Yang, 2004). From the viewpoint of applications to optical memory media and full color diaplays, it is desired to develop photochromic compounds that have sensitivity in the wavelength region of 650–830 nm (Irie, 2000; Gilat et al., 1993, 1995). We have previously reported three dithienylethenes with dicyano subsitituent: 1,2-bis[2-methyl-5-(2,2'-dicyanovinyl)-3-thienyl]-3,3,4,4,5,5- hexafluorocyclopent-1-ene, 2-ethyl analog and 2-butyl analog (Pu et al., 2003, 2005; Zheng et al., 2007), which have relatively long wavelength absorption spectrum (> 700 nm). In order to investigate systematically the substituent effect at the 2-position of the thiophene rings of diarylethenes on their photochemical properties, we have now synthesized the title photochromic diarylethene, (Ia) (Scheme 1), and its structure is presented here.

The molecular structure of the title compound (Ia) (Fig. 1) shows a photoactive anti-parallel conformation. The two n-pentyl groups are trans directed with respect to the central cyclopentene ring. Such a configuration is crucial for the compound to exhibit photochromic and photoinduced properties (Woodward & Hoffmann, 1970). The central cyclopentene ring assumes an envelope conformation. The distance between the two reactive C atoms (C4 and C19) is 3.834 (7) Å. This distance indicates the crystal can undergo photochromism to generate the closed isomer of diarylethene (Ib), because photochromic reactivity usually appears when the distance between the reactive C atoms is less than 4.2 Å (Kobatake et al., 2004). Crystal of (Ia) showed photochromic reaction coincident with the theoretical analysis. The colorless crystal of (Ia) turned to green upon irradiation with 365 nm UV light. When the green crystal were dissolved in hexane, the solution turned to green, and the absorption maximum was observed at 750 nm, which is the identical with that found in its closed-ring tautomer (Ib) (Scheme 2). The green color disappeared upon irradiation with appropriate wavelength visible light and the absorption spectrum of the solution containing the colorless crystal were the same as that found for the open-ring tautomer (Ia) with the absorption maximum at 356 nm.

Experimental

The title compound, (Ia), was synthesized by the Knoevenagel condensation reaction of diarylethene 1,2-bis(2-n-heptyl-5-formyl-3-thienyl)perfluorocyclopentene (1) (Scheme 3). First, compound (1) was prepared according to the procedure described in the previous paper (Zheng et al., 2007). Then to a stirred solution of compound (1) (0.1 g, 0.19 mmol) and malonodinitrile (0.025 g, 0.35 mmol) in anhydrous ethanol (5 ml), a very small quantity of piperidine was added dropwise at room temperature. The reaction mixture was stirred overnight at 323 K. Finally, the title compound was produced in 75.0% yield.