G. Barbarella et al., Rigid-core oligothiophene-S,S-dioxides with high photoluminescence efficiencies both in solution and in the solid state, CHEM MATER, 13(11), 2001, pp. 4112-4122
The photoluminescence (PL) frequencies and quantum efficiencies of dithieno
[3,2-b;2',3'-d]thiophene-4,4-dioxide (1), its 3,5-dimethyl derivative (2),
and the corresponding 4-oxide (3) are reported and discussed in relation to
their single-crystal X-ray structures. The peculiar packing modalities of
dioxides 1 and 2, based on dimeric units originated by short S . . .O conta
cts between molecules related by an inversion center, cause an unusually hi
gh bathocromic shift of PL frequencies from solution to solid state. This e
ffect is accompanied by a marked decrease in solid-state PL efficiencies (1
2% and 16%) compared to those in solution (75% and 77%). In monoxide 3 the
loss of local symmetry inherent to the change SO2 --> SO deeply modifies th
e self-assembly and PL properties, and the PL efficiency in the solid state
is close to that in solution. Ab initio calculations on the ground and exc
ited states of compound 1 were performed and compared to those of a conform
ationally mobile counterpart. Oligomers containing dithienothiophene 2 as i
nternal core were synthesized and found to be characterized by high PL effi
ciencies in the solid-state (up to 48%) as well as in solution (up to 85%).
The current-voltage and luminance-voltage plots of an electroluminescent d
iode fabricated with one of these new rigid-core oligothiophene-S,S-dioxide
s are reported.