Ruikui Chen

Photoinduced Intramolecular Charge Transfer and S2 Fluorescence in Thiophene-π-Conjugated Donor–Acceptor Systems: Experimental and TDDFT Studies†

Experimental and theoretical methods were used to study newly synthesized thiophene-pi-conjugated donor-acceptor compounds, which were found to exhibit efficient intramolecular charge-transfer emission in polar solvents with relatively large Stokes shifts and strong solvatochromism. To gain insight into the solvatochromic behavior of these compounds, the dependence of the spectra on solvent polarity was studied on the basis of Lippert-Mataga models. We found that intramolecular charge transfer in these donor-acceptor systems is significantly dependent on the electron-withdrawing substituents at the thienyl 2-position. The dependence of the absorption and emission spectra of these compounds in methanol on the concentration of trifluoroacetic acid was used to confirm intramolecular charge-transfer emission. Moreover, the calculated absorption and emission energies, which are in accordance with the experimental values, suggested that fluorescence can be emitted from different geometric conformations. In addition, a novel S(2) fluorescence phenomenon for some of these compounds was also be observed. The fluorescence excitation spectra were used to confirm the S(2) fluorescence. We demonstrate that S(2) fluorescence can be explained by the calculated energy gap between the S(2) and S(1) states of these molecules. Furthermore, nonlinear optical behavior of the thiophene-pi-conjugated compound with diethylcyanomethylphosphonate substituents was predicted in theory.

Two Novel Carbazole Dyes for Dye-Sensitized Solar Cells with Open-Circuit Voltages up to 1 V Based on Br−/Br3− Electrolytes

Dye-sensitized solar cells (DSCs) based on two novel carbazole dyes (TC301 and TC306) and a Br(-)/Br(3)(-) redox mediator in dried CH(3)CN solutions as electrolytes yielded a V(oc) of 1.156 V and a eta value of 3.68% and a V(oc) of 0.939 V and a eta value of 5.22% under simulated AM 1.5, respectively. The dyes TC301 and TC306 have more positive HOMO levels (1.59 and 1.38 V vs NHE) than the redox potential of Br(-)/Br(3)(-)-based electrolytes, which have sufficient driving force to regenerate dyes. Under similar conditions with an I(-)/I(3)(-) instead of a Br(-)/Br(3)(-) redox mediator, DSCs sensitized by the dyes TC301 and TC306 produced a V(oc) of 0.696 V and a eta value of 2.36% and a V(oc) of 0.621 V and a eta value of 4.10%, respectively.

Tuning of phenoxazine chromophores for efficient organic dye-sensitized solar cells

Through introducing an energy antenna system into a simple phenoxazine dye (TH301), a novel and efficient dye TH305 was designed and synthesized for application in a dye sensitized solar cell with prominent overall conversion efficiency of 7.7%.