Synthesis and photophysics of a broadband absorbing texaphyrin derivative bearing a Rhodamine 6G motif

A texaphyrin derivative with Rhodamine 6G attached (complex 11) via a CC bond was synthesized and characterized. The UV-vis absorption, emission and nanosecond transient absorption (TA) characteristics of this complex were systematically studied in acetone solutions. The photophysics of this complex was also compared with those of its precursor compounds texaphyrins 12 and 13 and the Rhodamine 6G derivative 3. The UV-vis absorption spectrum of 11 consists of both the characteristic Soret and Q bands of the texaphyrin derivative 13 and the identical absorption band from the Rhodamine 6G derivative 3. When excited at 550 nm (the major absorption band of Rhodamine 6G), 11 exhibits fluorescence bands from both the Rhodamine 6G component (582 nm) and texaphyrin component (802 nm), but the intensity of the 582 nm band dramatically reduced accompanied by a significant increase of the 802 nm band compared to those from 3 and 13, indicating electron/energy transfer from the singlet excited state of Rhodamine 6G. The ns TA spectrum of 11 resembles that of the texaphyrin derivative 13 but with both the bleaching band and absorption band red-shifted. The triplet lifetimes deduced from the decay of ns TA are quite similar for 11, 12 and 13, indicating the lack of interactions between the triplet excited states of the texaphyrin component and the Rhodamine 6G component. The broadband ground-state absorption of 11 from the visible to the near-IR region, and the possible electron/energy transfer from the singlet excited state of the Rhodamine 6G component to the texaphyrin component suggest that this complex could potentially be a broadband photosensitizer for dye-sensitized solar cell applications.