No abstract

Spin−orbit charge transfer intersystem crossing (SOCT-ISC) is a promising approach to develop heavy-atom-free triplet photosensitizers. However, designing a strong visible-light harvesting heavy-atom-free triplet photosensitizer with efficient ISC ability in various solvents is still challenging. Most of the SOCT-ISC triplet photosensitizers exhibit efficient ISC only in solvent of particular polarity. To address this challenge, herein, two triads (BDP-AN-C-CZ and BDP-AN-N-CZ), composed of carbazole (CZ), anthracene (AN), and bodipy (BDP) moieties, were devised. In these triads, the distance, relative orientation, and position of CZ with respect to the AN moiety were varied to study the effect on photophysical properties, especially on SOCT-ISC efficiency. Electrochemical studies, steady-state, and time-resolved spectroscopies confirmed a sequential photoinduced electron transfer (PET) process in the triads. The fluorescence of the BDP moiety is quenched and a red-shifted CT emission band is observed in the triads, due to the enhanced PET effect, compared to the reference BDP-AN dyad. We observed that the SOCT-ISC yield can be enhanced taking advantage of sequential electron transfer. The triad BDP-AN-C-CZ, in which the CZ moiety was directly linked to the AN moiety, shows an efficient ISC ability both in low-polarity and high-polarity solvents, and unity triplet quantum yield (Φ T ) was observed in dichloromethane. Femtosecond transient absorption spectroscopy confirmed the fast charge separation process (1.8 ps) in BDP-AN-C-CZ as compared to the other triad BDP-AN-N-CZ (4.8 ps) and the reference BDP-AN dyad (7.7 ps). The triads were used as triplet photosensitizers for triplet−triplet annihilation (TTA) upconversion, and high upconversion quantum yield (Φ UC = 18%) was observed. Interestingly, long-lived (τ DF = 118 μs) and solvent-dependent color-tunable TTA delayed fluorescence was observed in the case of BDP-AN-C-CZ.

The photophysical properties, especially the intersystem crossing (ISC) of two heavy atom-free BODIPY derivatives with twisted -conjugated frameworks (benzo[b]-fused BODIPY, BDP-B; and [a]phenanthrene-fused BODIPY, BDP-P) are studied with steady state and time-resolved optical and electron paramagnetic resonance (TREPR) spectroscopic methods as well as with ADC(2) theoretical investigations. Both derivatives show intense absorption of red light ( = 9.8  10 4 M 1 cm 1 at 640 nm for BDP-P). Interestingly, BDP-B is with planar -conjugation framework, but it displays weak fluorescence (F < 0.1%), shortlived singlet excited state (fluorescence lifetime, F = 0.2 ns) but long-lived triplet state (T = 132.3 s). In contrast, the more twisted BDP-P shows stronger fluorescence (F = 70%), longer singlet excited state lifetime (F = 6.4 ns), but shorter triplet state lifetime (T = 18.9 s). In contrast to helicenes (T = ca. 90%), the ISC of BDP-P and BDP-B is non-efficient (T < 23%). The electron spin selectivity of the ISC of the derivatives is different, manifested by the phase pattern of the TREPR spectra as AAEAEE and EEEAAA for BDP-B and BDP-P, respectively. The spatially confined T1 state wave function of the twisted molecule doesn't reduce the T1 state energy (1.441.61 eV), although the chromophore shows red-shifted absorption as compared to the native BODIPY (ca. 1.60 eV). This work demonstrated the twisted -conjugated framework does not necessarily induce efficient ISC and we found a dark singlet state for Bodipy, which is rare.

Four new complexes, [Zn(TIBTC)(DMA)]• [NH 2 (CH 3 ) 2 ] (1), [Cd(TIBTC)(H 2 O)]•[NH 2 (CH 3 ) 2 ]•DMA (2), [Cd 2 (TIBTC)(2,2′-bipy) 2 (HCOO)] (3), and [Cd 2 (DIBTC)(2,2′bipy) 2 (HCOO)] ( 4) (H 3 TIBTC = 2,4,6-triiodo-1,3,5-benzenetricarboxylic acid, H 3 DIBTC = 2,4-diiodo-1,3,5-benzenetricarboxylic acid, 2,2′-bipy = 2,2′-bipyridine, and DMA = dimethylacetamide), were successfully synthesized and characterized by elemental analysis, powder X-ray diffraction, infrared spectroscopy, ultraviolet− visible spectroscopy, and thermogravimetric analysis. Complexes 1 and 2 are three-dimensional supramolecular network structures, while complex 4 has a two-dimensional network structure. We preliminarily studied the fluorescence properties of the complexes and found that complexes 1−3 can detect thiamine hydrochloride, NACs, and Fe 3+ /Zn 2+ with high sensitivity and selectivity.

In accurately diagnosing Alzheimer’s disease (AD) and distinguishing AD from other dementia, the concentration ratio of amyloid-beta 42 (Aβ42) to Aβ40 is more reliable than the concentration of Aβ42 alone. For the multiplex PEC assay, generating an independent photocurrent of multiple targets on a single interface is a great challenge. Herein, an i-motif-based switchable sensing approach is proposed to construct a pH-regulated multiplex PEC immunosensor for Aβ42 and Aβ40 by using Bi-TBAPy as an efficient photoactive cathode material. An independent photocurrent signal of Aβ42 and Aβ40 is produced through the regulation of the electron-transfer tunneling distance by a pH-dependent configuration transition of the i-motif DNA. In a 96-well plate, immunological recognition of Aβ42 (or Aβ40) coupled with an enzymatic catalytic reaction produces an acidic (or alkaline) lysis solution, which triggers the formation and unravelment of the i-motif structure. The above configuration transition regulates the distance between Au NPs labeled SH-DNA and Bi-TBAPy, leading to PEC signal switching. Smart integration of the pH-responsive switchable DNA probe with a high-efficiency photocathode enables the precise monitoring of Aβ42 and Aβ40 at a single interface in a wide detection range (10 fg/mL ∼ 1 μg/mL and 1 pg/mL ∼ 1 μg/mL) with detection limit of 4.5 fg/mL and 0.52 pg/mL, respectively. The proposed i-motif-based switchable sensing strategy paves a new avenue for a multiplex PEC assay on a single interface, showing great prospects in bioanalysis and early disease diagnosis.