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A squaraine heterotriad consisting of three different covalently linked squaraine chromophores was synthesized, and its absorption spectra were interpreted in terms of Kasha's exciton coupling theory. Using the exciton couplings derived from model dyads (ca. 700 cm

We present a fully non-collinear 50 kHz shot-to-shot detected two-dimensional electronic spectroscopy setup for directly studying bi-exciton relaxation dynamics via 5th order signals. The measurements report on annihilation timescales at a single, perturbative excitation energy.

We directly compare nonlinear coherently and fluorescence-detected two-dimensional electronic spectra of electronically coupled squaraine heterodimers. By identifying signatures of multi-exciton nonequilibrium dynamics and delocalization, we establish grounds for interpretation of these nonlinear spectroscopy implementations.

A tetraphenylsquaraine was synthesized whose structure was elucidated by single crystal X-ray structure analysis. Unlike all known indolenine squaraines, the tetraphenylsquaraine shows an unusual nonplanar structure with the four phenyl groups pointing away from the squaric acid core in order to avoid steric congestion. This tetraphenylsquaraine was polymerized by a Yamamoto coupling to form a conjugated polymer with Xn = 38. The absorption spectra of this polymer are red-shifted compared to that of the monomer and show a J-type absorption band due to exciton coupling. Transient absorption spectra with fs-time resolution display a strong ground state bleaching signal with a peak on the red side rising concurrently with the decay of a peak on the blue side of an isosbestic point at 12 000 cm−1. This behavior is caused by energy transfer between two slightly different sections of the polymer with time constants of 0.3 and 2.6 ps. According to semiempirical calculations these different sections are stretched and slightly bent conformations of the polymer strand. Power dependent transient absorption measurements indicate exciton annihilation which also proves the excitons to be very mobile.

We describe the aggregate formation and optical properties of a star-shaped hexaarylbenzene with six squaraine chromophores (=hexasquarainyl benzene). Comprehensive concentration-dependence studies in acetone/CHCl3 mixtures reveal a strong propensity to form discrete dimeric aggregates with a high binding constant in excess of 106 m-1 . In this context, a large hypsochromic shift of almost 2700 cm-1 was found in the absorption spectrum, indicating H-type exciton coupling. The aggregate band is characterised by a very small band width of only 560 cm-1 , probably caused by exchange narrowing. Both experimental and computational methods were used to elucidate the supramolecular aggregate structure, which is assumed to consist of two stacked hexasquarainyl benzene monomers.

The linear and nonlinear optical properties of a series of oligomeric squaraine dyes were investigated by one-photon absorption spectroscopy (1PA) and two-photon absorption (2PA) induced fluorescence spectroscopy. The superchromophores are based on two indolenine squaraine dyes with transoid (SQA) and cisoid configuration (SQB). Using these monomers, linear dimers and trimers as well as star-shaped trimers and hexamers with benzene or triphenylamine cores were synthesised and investigated. The red-shifted and intensified 1PA spectra of all superchromophores could well be explained by exciton coupling theory. In the linear chromophore arrangements we also found superradiance of fluorescence but not in the branched systems. Furthermore, the 2PA showed enhanced cross sections for the linear oligomers but only additivity for the branched systems. This emphasizes that the enhancement of the 2PA cross section in the linear arrangements is probably caused by orbital interactions of higher excited configurations.