Through-Space Exciton Delocalization in Segregated HJ-Crystalline Molecular Aggregates

Abstract

Exciton delocalization relates to many important photophysical processes such as excitation energy transfer, charge separation, and singlet fission. Here, we analyze the exciton delocalization through the photophysical measurements of the molecular crystal 2,2′-(thiazolo [5,4-d]thiazole-2,5-diyl)bis(4-methylphenol) (m-MTTM), which is the segregated HJ-aggregate confirmed by the calculation of exciton coupling along each direction in the crystal structure. Linearly polarized steady-state absorption spectroscopy verifies that the red-shifted optical transition majorly arises from the aggregates unparalleled to the a-axis. In addition, the temperature-dependent emission spectra show the increase of 0−0 versus 0−1 vibronic emission ratio as the temperature decreases with the coherence number equaling 2.2−1.0 at 140−200 K, which is the characteristic behavior of J-aggregates. To elaborate these observations, we carry out the simulation with the Holstein-type Hamiltonian considering short-range chargetransfer-mediated couplings (perturbative regime) under the two-particle approximation, showing that the 3 × 3 laminar-like aggregates in the ac-plane and the 3 × 3 × 2 three-dimensional aggregates fit well with the emission spectrum at 140 K. In the 3 × 3 aggregates, the coherence function in the ac-plane shows the in-phase correlation along (1,0,−1), elucidating how J-aggregates form in segregated HJ-aggregates with dominant positive coupling. Under the strong intralayer out-of-phase correlation, the 3 × 3 × 2 aggregates demonstrate that the vibronic coupling has a great impact on the interlayer correlation. Furthermore, the coherence function along (0,1/2,−1/2) and (−1,1/2,−1/2) exhibits the thermal-activated phase flipping. These discoveries pave the ways for further manipulations of exciton delocalization in three-dimensional molecular solids.

Flexible and Transparent Oligothiophene-o-Carborane-Containing Hybrid Films for Nonlinear Optical Limiting Based on Efficient Two-Photon Absorption

“…Derivatives 1 – 1 , 1 – 2 , and 2 – 1 were successfully synthesized and exhibited intense solid-emissive fluorescence in the red spectral region. The covalently linked fluorophores simultaneously exhibited dual emission from the LE and ICT or induce excimer states in solution . These results definitively show that the planarity of the aryl group appended to o -CB has a decisive effect on the efficiency of the ICT-based radiative decay.…”

“…The covalently linked fluorophores simultaneously exhibited dual emission from the LE and ICT or induce excimer states in solution. 57 These results definitively show that the planarity of the aryl group appended to o-CB has a decisive effect on the efficiency of the ICT-based radiative decay. As a consequence, a variety of useful functions for developing advanced optical materials were obtained.…”

The Observation of Interchain Motion in Self-Assembled Crystalline Platinum(II) Complexes: An Exquisite Case but By No Means the Only One in Molecular Solids

“…In other words, the multiple local minima observed in the electronic ground and excited states are associated with a very subtle change of the interchain distances. This interchain interaction relates to the multidirectional exciton coupling of Pt­(fppz) 2 with two-dimensional brick-wall-type arrangement (see packing structure in Figure b). ,, These results thus provide a new understanding for the self-assembled Pt­(fppz) 2 complexes. Many other self-assembled Pt­(II) complexes and molecular solids with adjustable interchain distances may exhibit similar features, rendering their optoelectronic versatility.…”

Intrachain Exciton Motion Can Compete with Interchain Hopping in Conjugated Polymer Films with a Strong J-Aggregate Property

“…Figure b shows the temperature dependence of the photoluminescence (PL) intensity ratio I 0–0 / I 0–1 of a pristine PNOz4T film, where I 0–0 and I 1–1 represent the PL intensities of the 0–0 and 0–1 emission bands, respectively. The I 0–0 / I 0–1 value increases with a decrease in temperature until 150 K, and then decreases with a decrease in temperature below 150 K. This complex temperature dependence is a characteristic of the HJ-aggregate proposed by Spano et al, who considered intrachain interaction as J-coupling, whereas interchain interaction was described as H-coupling. − In this model, the PL intensity ratio peaks at a threshold temperature as a competition between an H-like thermally activated term and a J-like thermally deactivated term. Therefore, we conclude that PNOz4T is likely to form HJ-aggregates owing to its relatively high backbone planarity.…”