Issue 6, 2015

Polymorph crystal packing effects on charge transfer emission in the solid state


Condensation of 1,8-naphthalic anhydride with N,N-(dimethylamino)aniline produced the donor–acceptor compound DMIM, which crystallised from a chloroform–diethyl ether mixture to afford two different coloured crystal polymorphs. Crystals for one polymorph are small and green, whereas the other crystals are orange and needle-like. X-ray crystal structures for both polymorphs were determined. The donor N,N-dimethylaniline and acceptor naphthalimide groups are twisted with respect to each other; the degree of twist is marginally different for the two structures. The orange crystal polymorph crystallises in the monoclinic space group C2/c and contains two slightly different molecular conformers in the unit cell (calculated density is 1.410 g cm−3). The green crystal polymorph crystallises in the triclinic space group P[1 with combining macron] and contains only one type of molecule in the unit cell (calculated density is 1.401 g cm−3). The crystal packing motifs for the two polymorphs are subtly different, explaining the small variance in the observed densities. Very weak room temperature emission was observed for DMIM in a CHCl3 solution, but crystals deposited on a glass slide glowed when irradiated at 488 nm using a fluorescence microscope. Disparate solid-state emission spectra and lifetimes for the two polymorphic crystal forms are observed for the dyad. The emission is assigned to charge recombination fluorescence from a charge transfer state.

Graphical abstract: Polymorph crystal packing effects on charge transfer emission in the solid state

Supplementary files

Article information

Article type
Edge Article
31 Mar 2015
18 Apr 2015
First published
20 Apr 2015
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2015,6, 3525-3532

Author version available

Polymorph crystal packing effects on charge transfer emission in the solid state

X. He, A. C. Benniston, H. Saarenpää, H. Lemmetyinen, N. V. Tkachenko and U. Baisch, Chem. Sci., 2015, 6, 3525 DOI: 10.1039/C5SC01151E

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