Unravelling the Role of Water in Ultrafast Excited‐State Relaxation Dynamics within Nano‐Architectures of Chlorophyll a

Abstract

Water plays a pivotal role in structural stability of supramolecular pigment assemblies designed for natural light harvesting (for example, chlorosome antenna complex) as well as their artificial analogs. However, the dynamic role of water in the context of excite‐state relaxation has not been explored till date, which we report here. Using femtosecond transient absorption spectroscopy, we investigate the excited‐state dynamics of two types of nano‐scale assemblies of chlorophyll a with different structural motifs, rod‐shaped and micellar assemblies, that depend on the water content. We show how water participates in excess energy dissipation by vibrational cooling of the non‐thermally populated Qy band at different rates in different types of clusters but exhibits no polar solvation dynamics. For the micelles, we observe a bifurcation of stimulated emission line shape, whereas a positive‐to‐negative switching of differential absorption is observed for the rods; both these observations are correlated with their specific structural aspects. Density functional theory calculations reveal two possible stable ground state geometries of dimers, accounting for the bifurcation of line shape in micelles. Thus, our study elucidates water‐mediated structure–function relationship within these pigment assemblies.

Unravelling the excited state dynamics of monofunctionalized mono- and distyryl-BODIPY and perylenediimide dyads

“…To obtain a detailed understanding of the quenching mechanism in these dyads, femtosecond transient absorption (TA) measurements 60 were performed. The measurements were performed with dyads as well as their constituent reference compounds.…”

“…In this section, the detailed excited state dynamics involved in dyad 1 and dyad 2 for MSBDP 6 and DSBDP 9 excitation respectively will be discussed, as in some of our previous work. 60 TA spectra of constituent reference compounds of both the dyads are shown in the ESI † in Fig. S17.…”

Elucidating the Structure–Property Relationship and Ultrafast Exciton/Charge Carrier Dynamics of Layered Cs4CuSb2Cl12Double-Perovskite Microcrystals

“…49,62,63 Thus, we obtain different time components (τ 2 and τ 3 ) for ESA and GSB2. At longer time delay, the narrowing of the ESA band is due to vibrational cooling of the population, 63,64 while the spectral broadening of the GSB1 band is likely due to the carrier scattering induced by the high concentration of the holes near valance band maxima, indicating thermalization of holes. 63 To take into account the overlapping spectral features of GSB and ESA bands, we performed the global analysis of pump−probe data ranging from 350 to 550 nm using a sequential model (see Figure S11(Section SI-5)).…”

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

“…A broadband femtosecond transient absorption spectrometer (TAS, Newport) is used for ultrafast relaxation dynamics, the details of ChemPhysChem which may be found elsewhere. [51,52] In brief, an excitation laser pulse centered at 640 nm with pulse-width ~30 fs is generated by a commercial non-collinear optical parametric amplifier (Topas White, Light conversion), seeded by a ~55 fs laser pulse centered on 800 nm from a Ti: Sapphire regenerative amplifier (Libra, Coherent). Part of the 800 nm laser pulse is focused on a CaF 2 crystal to generate a broadband white light probe pulse.…”