1. UNPRECEDENTED SOLVATED FORM OF TPB
SHOWING CHANNELS ACCESSIBLE TO GUEST
EXCHANGE
Domenico Crocco, Alessia Bacchi, Mauro Carcelli, Alberto Girlando
Dipartimento di Chimica G.I.A.F., Parma University, Viale delle Scienze 17/A, 43124 Parma
E-mail: domenico.crocco@nemo.unipr.it
Introduction: Our study is based on polymorphism of the TPB(1,1,4,4-tetraphenyl-1,3-butadiene) organic molecule of
considerable practical interest, because of its luminescent properties. Interestingly it has been shown that TPB displays
luminescence also in the crystalline state, favoured by the packing arrangement that aligned the transition dipoles in the
correct orientation. TPB is currently known in three polymorphs α, β, γ,[1] and the latter two present a very similar
crystal packing based on arrays of parallel molecules, whereas the α form is arranged in a herringbone pattern. The
molecular conformation on the β and γ form is identical (Figure 1). The β form is the most promising for practical
applications because its crystal packing favors photoluminescence at best, while the alpha form is thermodynamically
more stable.
Conclusions: The loss of the guest transforms the solvate phase in the γ form, providing a clean and quantitative synthetic
method to obtain selectively this polymorph that is otherwise difficult to prepare by precipitation due to the preponderance
of the useless form.
In this work we have obtained a particularly interesting solvated form containing cyclohexane as a guest. Most
interestingly the guest is arranged in well ordered arrays inside channels throughout the crystal packing; the system is
very unstable and looses cyclohexane in a few minutes after removal from the solution due to the fact that the channels
are not able to trap the guest with a sufficient stability. The loss of the guest transforms the solvate phase in the γ.
a=6.259(2)
b=22.164(4) β=96.349(4)
c=7.362(3)
ALPHA FORM BETA FORM GAMMA FORM
a=9.736(5)
b=8.634(2) β =97.11(4)
c=24.480(13)
a=10.110(1) α=103.64(1)
b=10.851(2) β=94.95(1)
c=9.820(2) γ=99.31(1)
Another key result of this work is that when the
solvate system is exposed to cyclohexanone vapors
it does not decompose but exchanges cyclohexane
with cyclohexanone without loosing crystallinity
(νC=O = 1709.59 cm-1). This shows that the channels
are stabilized by the presence of cyclohexanone.
Gamma Form
[1] Girlando, A.; Iannelli, S.; Bilotti, I.; Brillante , A.; Della Valle, R,G.; Venuti, E.; Campione , M.; Mora , S.; Silvestri,L.; Spearman, P.; Silvia , T . Cryst. Growth Des., 2010 , 10 (6), 2752–2758