C O M M U N I C A T I O N S
state (µg ) 0.09 D), as expected. On the other hand, calculated
dipole moments of E (EWG)/S (EDG) PEs in the excited state do
not exceed those in the ground state (for example, µe ) 0.66 D
and µg ) 1.99 D for 11; see Supporting Information for others).
Such a dipole moment change in the excited and ground states
of E (EWG)/S (EDG) PEs appears to be responsible for little solvent
dependency to the spectra of 11 and 12. From these arguments, it
is inferred that the acetylenic structure of E (EWG)/S (EDG) PEs
in the ground state (see Supporting Information) may also be held
in the excited state as reported for TriPE.13
In conclusion, we succeeded in the creation of highly efficient
light emitters by E (EWG)/S (EDG) modification of rod-shaped
OPEs. We also made very interesting findings on the relationships
between (1) Φf and Hammett σ constant, and (2) light-emitting
characteristics (λem, Φf) and solvent polarity. These should be
valuable for the molecular design of highly efficient light emitters.
Figure 1. The relationship between quantum yield (Φf) and substituent
constant for the electron-withdrawing substituent X (σp-X) for E (EWG)/S
(EDG) PEs.
Acknowledgment. This work was supported by Grant-in-Aid
for Creative Scientific Research (No. 16GS0209) and Scientific
Research (No. 16550131) from the Ministry of Education, Science,
Sports, and Culture of Japan.
Supporting Information Available: Synthesis, NMR data, HR MS
data, absorption and fluorescence spectra, plot of λem versus σ and Φf
versus σ, and MO calculation for oligo-PEs modified by donor and
acceptor groups. This material is available free of charge via the Internet
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Figure 3. AM1 HOMO and LUMO diagrams for 11 and 12.
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It is to be noted that contrary to the reported cases,4b,d,12 Φf, λem
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λ
CHCl3, THF, CH3CN, and DMF (change in solvent polarity) (see
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HOMO/LUMO diagrams (Figure 3 and Supporting Information).
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