Fluorescence lifetime and electron transfer in cyclobutenediylic dyes

Radiative and Nonradiative Excited State Relaxation Channels in Squaric Acid Derivatives Bearing Differently Sized Donor Substituents: A Comparison of Experiment and Theory

“…Squaraine derivatives are popular dyes in the visible region used for photosensitization in imaging processes − and in solar energy conversion. , Their photophysics, however, have only recently started to raise interest, − and most of these studies focus on squaraines bearing anilino donors like SQ-DMA, although a large variety of dyes with quite different donors are available. − Whereas SQ-DMA is known to exhibit quite strong fluorescence, ,,− nothing has been reported about the fluorescence properties of the squaraine compound SQ-DP and little is known 23 about the fluorescence of cyanine-type squaraines like SQ-IN (Scheme ). On the other hand, there are some reports with respect to the synthesis and absorption data of these compounds in the literature. − We therefore undertook some systematic photophysical investigations regarding the luminescence properties of these squaraines.…”

Photophysical Properties of Squaraine Derivatives: Evidence for Charge Separation

“…Colored squaric acid derivatives (squaraine dyes) have gained some importance due to their numerous applications − and in solar energy conversion. , Several studies have been made regarding their photophysical properties. − Some of these studies reported multiple fluorescence with three bands, the ratio of which changed with increasing solvent polarity and with the substitution pattern of the squaraine dye. , One of these bands was assigned to a twisted intramolecular charge transfer (TICT) state; − for reviews on TICT states see refs −25. Other researchers, however, did not report multiple bands, − so that the situation remains unclear.…”

“…They are used for photosensitization in imaging processes − and in solar energy conversion. , Several studies have been made regarding their photophysical properties. − Some of these studies reported multiple fluorescence with three bands, the ratio of which changed with increasing solvent polarity and with the substitution pattern of the squaraine dye. , One of these bands was assigned to a twisted intramolecular charge transfer (TICT) state; − for reviews on TICT states see refs −25. Other researchers, however, did not report multiple bands, − so that the situation remains unclear. Although aggregation phenomena play an important role in the present literature (refs , and references therein), the nonradiative decay behavior of the uncomplexed dye systems is still not well understood.…”