Solvatochromism and Solvation Dynamics of Structurally Related Cyanine Dyes

Abstract

Absorption, fluorescence, and magic-angle pump-probe experiments characterize the solvatochromism and relaxation dynamics of three structurally related near-infrared tricarbocyanine dyes (HDITCP, IR125, and IR144) in solution. Agreement with solvatochromic theory is found in solvents where the conductivity approximately matches that predicted for complete ionic dissociation. The nonpolar solvatochromism of HDITCP and IR125 allows the polar solvatochromism of the IR144 absorption spectrum to be attributed to a specific functional group. Resonance structure arguments predict a dipole moment decrease upon electronic absorption by IR144, consistent with the observed solvatochromism. Assuming a point dipole, spherical cavity reaction field model, self-consistent feedback between the solvent and the polarizable IR144 solute accounts for 1/2 to 1/3 of the observed polar solvent shifts. A geometry change in the excited state leads to nearly nonpolar solvatochromism in the IR144 emission spectrum. Femtosecond magic-angle pump-probe transients show similar underdamped intramolecular vibrational quantum beats in all three molecules, but find solventdependent overdamped responses on a picosecond time scale in all three dyes. The quantum beat decays determine inhomogeneous vibrational dephasing times of a few picoseconds. Vibrational relaxation, nonpolar solvation, and dielectric relaxation all take place on similar time scales, but the picosecond relaxations are all slower and of larger amplitude for IR144 (polar solvatochromism) than HDITCP (nonpolar solvatochromism). In contrast to HDITCP, IR144 has a prominent solvent-dependent "coherence spike" near T ) 0 which is attributed to femtosecond polar solvation dynamics.

Visualizing overdamped wavepacket motion: Excited-state isomerization of pseudocyanine in viscous solvents

“…S 1 absorption spectrum of 1122C undergoes a slight ($145 cm À1 ) bathochromic shift. This 'general red shift' was already observed for 1122C [38] as well as for many other open-chain polymethine dyes, and is due to dispersive interactions [39][40][41][42]. We note that the S 0 ?…”

“…2230 cm À1 ) is found to be large compared to the absorption of related dyes with a longer, unsubstituted polymethine chain [13,32,[39][40][41][42]. In addition, the observation of an unstructured and broad emission band with a large Stokes-shift (3390 cm À1 ) hints to significant geometrical rearrangements from the absorptive to the emissive excited-state geometry.…”

Influence of Substituent and Solvent on the Radiative Process of Singlet Excited States of Novel Cyclic Azacyanine Derivatives

“…Stokes' shift was estimated to be 45 nm or 7,138 cm −1 (see Table 1). Cyanine based dyes usually exhibit sensitive solvatochromic behaviour in which the relative intensity of emission bands is dependent on solvent polarity [32][33][34][35][36].…”

“…Several groups have used various tricarbocyanine dyes in nonlinear optical experiments to characterize solvation time scales and reached different conclusions about the role of intramolecular interactions and solvent relaxation in the observed signals [34,35]. The impact of solvent polarity on the electronic spectral characteristic of cyanine dyes has been extensively investigated [36].…”

Covalent bonding and photochromic properties of double-shell polyurethane-chitosan microcapsules crosslinked onto cotton fabric

“…They are susceptible to environmental factors such as the pH (Mohammadi et al 2012), oxidation, irradiation and temperature, which can result in a change in the position, intensity and shape of the absorption bands (Feczkó et al 2012;Salaün et al 2009;Samoylova et al 2013). The influences result in poor photochemical fatigue and deterioration after numerous repetitive cycles of irradiations (Dodsworth and Lever 1990;Yu et al 2002). Encapsulated photochromic dyes can eliminate the resulting poor fatigue resistance problems, allowing sensitive material to be physically enveloped in a protective matrix or wall materials in order to protect the core materials from reactive and corrosive environments (Bobrovsky et al 2001;Kim et al 2006;Mysliwiec et al 2011;Pardo et al 2008).…”