A mechanophysical phase transition provides a dramatic example of colour polymorphism: the tribochromism of a substituted tri(methylene)tetrahydrofuran-2-one

Table 4 Molecular energies, HUMO-LUMO gap and the predicted wavelengths associated with the first excited states

Molecule	Absolute energies ^a(Hartree)	Relative energies ^akcal/mol	HOMO LUMO ^aGap (eV)	Gas phase 1 ^stExcited state ^b(eV)	COSMO 1 ^stExcited state ^b(eV)	Adiabatic Correction ^c(eV)
I	−1146.053748468		2.58	3.71	3.38	0.53
II	−1223.470314612		1.55	2.61	2.41	-^d
IIIa	−1300.807815239	0.8	2.49	3.63	3.16	0.78
IIIb	−1300.809021877	0.0	1.45	2.46	2.23	-^d
IV	−1340.117586577		2.40	3.47	3.05	0.73

^aThe energies are based on calculations using the BLYP density functional with a dispersion correction. ^bThe excited state energies are calculated using time dependent DFT with the B2PLYP functional at the ground state optimised geometry. ^cThe adiabatic correction is the excited state energy change on going from the optimised geometry of the excited state to that of the ground state. ^dThe geometry optimisation failed to converge.

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