Ultrafast Excited-State Dynamics of Tricarbocyanine Dyes Probed by Two-Dimensional Electronic Spectroscopy: Polar Solvation vs Photoisomerization

Abstract

Photophysical properties of tricarbocyanine dyes in various solvents have been widely investigated using a variety of spectroscopic tools. However, the presence of several ground-state isomers and interconversion between these isomers on an ultrafast timescale upon photoexcitation render unambiguous assignment of spectral features quite difficult. In this work, ultrafast excited-state dynamics of two tricarbocyanine dyes in two solvents, DNTTCI and IR140, in ethanol and ethylene glycol, are studied by twodimensional electronic spectroscopy (2DES). We present a detailed discussion on design and calibration of the 2DES apparatus and on the method for data processing by phase-cycling. For DNTTCI we report a method to obtain solvation correlation function, the nature of which is found to be strongly dependent on the excitation frequencies; a blue-shifted spectrum at early time is observed and explained based on preferential emission from a subset among various isomers having overlapping spectral features. For IR140 in ethanol, four isomers with distinct spectral features are identified, and most importantly, three of these isomers were found to interconvert upon photoexcitation which completes within 100 fs and is explained based on a kinetic model of consecutive chemical reaction. Density functional theory calculations show the presence of several ground-state isomers for both these dyes. Through this work we demonstrate how 2DES can help us to decipher distinct excited-state photophysics in two carbocyanine dyes, polar solvation and photoisomerization, by resolving spectral congestion without sacrificing time resolution.

Human Serum Albumin Dimerization Enhances the S2 Emission of Bound Cyanine IR806

“…Based on qualitative agreement with the experiment, the minima S 2 min-1 and S 2 min-2 correspond to the emissive states S 2 H and S 2 L , respectively, in line with the work of Laboe et al 5 Electronic structure calculations helped us understand the structural features of the ground and excited states of IR806. While cis−trans isomers are known to contribute to the spectroscopy of cyanine dyes, 46,47 we did not consider the contribution of different cis−trans configurations for every carbon in the polymethine chain. The energy difference for several different conformers, depicted in Figure S11, is given in Table S2.…”

Effect of Nanoscale Confinement on Ultrafast Dynamics of Singlet Fission in TIPS‐Pentacene

“…As a final note, though there exists a distribution of sizes for the NPs, no overlap between these distributions is observed indicating distinct dynamics within each NP. Of course, such distributions would mean that there is inhomogeneity as well heterogeneity in the system which can only be well resolved using excitation frequency‐dependent studies (as in, 2DES [57] not captured by pump‐probe measurements presented here.…”

Virtual Issue on Ultrafast Spectroscopy

“…14 The same method was used to monitor ultrafast excited state interconversion between isomers. 15 Understanding ultrafast excited state dynamics is important in characterizing photonic materials. Electronic excitation dynamics in conducting polymers was modeled on an ultrafast time scale.…”

“…2DES was used to study the coupling between electronic states in Chlorophyll a yielding important information for unravelling spectra in more complex chlorophyll aggregates . The same method was used to monitor ultrafast excited state interconversion between isomers …”