Fully Conjugated Porphyrin Glass: Collective Light-Harvesting Antenna for Near-Infrared Fluorescence beyond 1 μm

Abstract

Expanded π-systems with a narrow highest occupied molecular orbital–lowest unoccupied molecular orbital band gap encounter deactivation of excitons due to the “energy gap law” and undesired aggregation. This dilemma generally thwarts the near-infrared (NIR) luminescence of organic π-systems. A sophisticated cofacially stacked π-system is known to involve exponentially tailed disorder, which displays exceptionally red-shifted fluorescence even as only a marginal emission component. Enhancement of the tail-state fluorescence might be advantageous to achieve NIR photoluminescence with an expected collective light-harvesting antenna effect as follows: (i) efficient light-harvesting capacity due to intense electronic absorption, (ii) a long-distance exciton migration into the tail state based on a high spatial density of the chromophore site, and (iii) substantial transmission of NIR emission to circumvent the inner filter effect. Suppression of aggregation-induced quenching of fluorescence could realize collective light-harvesting antenna for NIR-luminescence materials. This study discloses an enhanced tail-state NIR fluorescence of a self-standing porphyrin film at 1138 nm with a moderate quantum efficiency based on a fully π-conjugated porphyrin that adopts an amorphous form, called “porphyrin glass”.

Trimethylsilanolate-Promoted Activation of Alkynyl Trimethylsilanes: Hiyama-Type Sonogashira Cross-Coupling for the Synthesis of Arylene–Ethynylene-Linked Porphyrin Arrays

“…Our exploration is conducted for the synthetic conditions of the cross-coupling reaction of bromoporphyrin 2 with 9,10-bis­(trimethylsilylethynyl)­anthracene 4 Ant as the electron-rich bridging unit (Scheme ). In our previous study employing the typical Sonogashira cross-coupling conditions in diisopropylamine (Route B ), the isolated yield of the 9,10-anthrylene–ethynylene-linked porphyrin dimer 1 Ant was very low (5%) because of the occurrence of the Glaser homocoupling as a side reaction . The nearly identical 9,10-anthrylene–ethynylene-linked porphyrin dimer was originally synthesized by the Stille cross-coupling in 46% yield in the pioneer work by Anderson and coworkers .…”

“…The color of the solution of 1 Ant in toluene was altered from dark green to brown as the concentration increased, suggesting self-aggregation. In our previous report, 1 Ant showed somewhat broad 1 H NMR signals in CDCl 3 , while pyridine- d 5 as the axially coordinating ligand sharpened the signals as follows. 1 H NMR (CDCl 3 with “2 equiv of pyridine- d 5 ”, 500 MHz): δ 10.09 (d, 4H, J = 4.5 Hz; pyrrole-β), 9.75 (d, 2H, J = 4.5 Hz; pyrrole-β), 9.48 (dd, 4H, J = 6.7, 3.1 Hz; anthrylene), 9.17 (d, 2H, J = 4.5 Hz; pyrrole-β), 9.05 (d, 2H, J = 4.5 Hz; pyrrole-β), 7.97 (dd, 4H, J = 6.7, 3.1 Hz; anthrylene), 7.45 (s, 8H; meso -Ar), 4.41–4.30 (m, 8H; p -ArO–C H 2 ), 4.22–4.13 (m, 16H; m -ArO–C H 2 ), 2.13–0.81 (m, 270H; aliphatic chains and TIPS).…”

“…Incorporating porphyrins into the ethynylene-conjugated π systems is privileged to the state-of-the-art optoelectronic functional materials. − The meso -ethynylene-conjugated porphyrins now garner considerable attention as the potential photosensitizers in photovoltaic studies due to the ideal spectral properties reaching to the near-infrared region. − Our research interest has been devoted to unprecedented features of morphologically controlled meso -ethynyl porphyrins. − For the modular synthesis of the meso -ethynylene-conjugated porphyrins, the Sonogashira cross-coupling reaction is also the principal protocol despite the possible structural defects arising from the intrinsically competitive Glaser homocoupling. However, the main research subjects have hitherto been focused on excellent functions of the meso -ethynylene-conjugated porphyrins, and the synthetic procedures have been relatively overlooked.…”

“…The elastic nature of the side chains significantly improves the solubility of the porphyrin ring in a nonpolar solvent and imparts a glassy nature to the porphyrins under solvent-free conditions. , Due to the nonpolar character of the porphyrin derivatives with an exceptional molecular size, the difference in both the polarity and molecular size of each target and side products is almost overwhelmed by the properties of the porphyrin unit. Then, the formidable purification using size-exclusion chromatography (SEC) is required to ensure the purity of 1 π satisfactory to photophysical investigations. , Therefore, the improved synthetic protocols of the Sonogashira cross-coupling reaction will open a new avenue to develop porphyrin-based materials. In our preceding study, we found that dichloromethane (DCM) is an effective solvent to minimize the Glaser homocoupling in Route B1 for the synthesis of 1 π in some cases. , This study extends the scope of the solvent-modulated approach (Route B1 ).…”

Mechanistic Understanding of Entanglement and Heralding in Cascade Emitters

“…The structure of the emission spectrum and the tail behavior of the density is in agreement with a previous work. 46 The bimodal shape of the spectrum originates from overlap of the two emissions as can be explained based on the contribution of each state according to its density of states. In this figure, and elsewhere in this paper, we performed our calculations using parameters in the same range as polarization-entangled photon pairs from a biexciton cascade from a single InAs QD embedded in a GaAs/AlAs planar microcavity.…”