In this research, the spectroscopic properties of a metal-free dye based on the indoloquinoxaline has been evaluated. To describe the behavior of this molecule against the radiation of sunlight, time dependent-density functional theory (TD-DFT) by the Gaussian 09 program [1] was applied. To obtain more accurate results, all calculations were performed at the M062X/6-311++(2d,2p) level of theory. The probability of electron transfer and the ability of the studied compound were estimated at different frequencies of sunlight. The corresponding compound can absorb the wavelengths from 340 to 440 nm. It shows two peaks at 360 and 410 nm. Both of the maximum absorption intensities are equal to the highest light harvesting efficiency (LHE) of the studied molecule. It means that the dye has a greater ability to harvest the sunlight in the wavelengths of 360 and 410 nm. Fig. 1 shows the behavior of the LHE as a function of different wavelengths of light.

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