Photophysical and electrochemical properties of 1,7-diaryl-substituted perylene diimides.
Substituent effects on the photophysical and electrochemical properties of 1,7-diaryl-substituted perylene diimides (1,7-Ar(2)PDIs) have been carefully explored. Progressive red-shifts of the absorption and emission maxima were observed when the electron-donating ability of these substituents was increased. Linear Hammett correlations of 1/lambda(max) versus sigma(+) were observed in both spectral analyses. The positive slopes of the Hammett plots suggested that the electronic transitions carry certain amounts of photoinduced intramolecular charge-transfer (PICT) character from the aryl substituents to the perylene diimide core which leads to the reduction of the electron density on the substituents. The substituent electronic effects originated mainly from the perturbation of the core PDI HOMO energy level by the substituents. This conclusion was supported by PM3 analyses and confirmed by cyclic voltammetry experiments. More interestingly, the Ph(2)NC(6)H(4)-substituted PDI, 4i, showed an unusual dual-band absorption that spans from 450 to 750 nm. We tentatively assigned these two bands as the charge-transfer band and the PDI core absorption, respectively.
Chao
Chun-Chieh
CC
Department of Chemistry and Institute of Polymer Science and Engineering, National Taiwan University, Taipei, Taiwan 106, ROC.
Leung
Man-kit
MK
Su
Yuhlong Oliver
YO
Chiu
Kuo-Yuan
KY
Lin
Tsung-Hsien
TH
Shieh
Shwu-Ju
SJ
Lin
Shien-Chang
SC