Prospects for useful fission from singlet states higher than S₁ in aggregated organic chromophores

Abstract

The few known reports and the likely prospects of finding new efficient routes to exciton fission from higher excited singlet states, Sn (n > 1), are reviewed. Aggregates of molecules...

An Exploration of Substituent Effects on the Photophysical Properties of Monobenzopentalenes

“…Typically, as Kasha's rule would dictate, excitation at higher energy would result in rapid deactivation to the lowest excited state, [61,62] which here is non-emissive. The presence of emission at energies above the HOMO-LUMO gap provides an unusual property that is often sought after for molecular photonics, [63,64] particularly for OLEDs. This highenergy emission was influenced substantially by the substituents (Figure 5, Table 2).…”

Activated Singlet Fission Dictated by Anti-Kasha Property in a Rylene Imide Dye

“…SF from a hot S n state remains thermodynamically favorable even when the E (T 1 ) is larger than half of E (S 1 ), offering an avenue to raise the triplet energy of SF materials. , Previous studies have demonstrated the operation of activated SF in conjugated polymers, − carotenoid derivatives, , tetracene, rubrene, − and other systems. − Recently, Gurzadyan and Sun et al observed that the rate of activated SF could be competitive with the vibrational relaxation to low-energy states in the solid state of perylene , and its cofacial dimer under high pump energy (250 nm) or with the assist of two photon absorption. However, the main issue to achieve SF from the higher excited electronic states lies in the suppression of competing decay channels of the S n states ( n ≥ 2), , which usually undergo ultrafast internal conversion (IC) to the lowest singlet excited states within subpicoseconds, as described by Kasha’s rule (Figure a) . The lack of an effective way to tune the decay of S n prevents the rational design of materials capable of efficient SF from higher energy excited states.…”

“…Studies of the underlying mechanism of anti-Kasha fluorescence in molecular entities have established that slowing down the S n → S 1 IC process with a large energy gap between S n and S 1 is an effective approach . The prolonged S n lifetime with reduced IC rate can potentially open up other decay channels, for example, SF from the S n state (Figure b). ,, Very recently, Ottosson et al delved into the anti-Kasha properties of azulene and its derivatives and unveiled the critical role of (anti)­aromaticity in modulating the S 2 –S 1 energy gap . The observation of (anti)­aromaticity-dependent anti-Kasha behavior provides valuable insight into designing novel materials capable of efficient SF from upper singlet excited states.…”

Ratiometric Chemosensors That Are Capable of Quantifying Hydrostatic Pressure Stimulus: A Case of Porphyrin Tweezers

“…As shown in Figure a (top), ratiometric signaling, that is, using the S 1 /S 2 ratio, may provide opportunities to fabricate ratiometric solution-state chemosensors. Among the many emissive organic molecules, fluorophores that emit S 2 fluorescence are limited; however, porphyrin chromophores appear to be the best candidates because the S 1 and S 2 emissions are equally observed rather than azulenes or other S 2 emitters. − Therefore, as shown in Figure a (bottom), we hypothesized that every porphyrin unit connected by a flexible linker should interact with each other under hydrostatic pressurization. Berova et al reported that porphyrin tweezers with different scaffolds can trap shorter and longer diamines at atmospheric pressure (0.1 MPa). , This fact strongly reinforces our working hypothesis that such porphyrin tweezers dynamically change in response to hydrostatic pressure, that is, open-closed equilibrium.…”