Photosensitization Ability of 1,7-Phenanthroline Based Bis−BODIPYs: Perplexing Role of Intramolecular Rotation on Photophysical Properties

Abstract

1,7-Phenanthroline based bis−boron dipyrromethenes (bis−BODIPYs) B1 and B2 obtained via small substitutional changes (−Cl/–SCH3) have been described. The effect of restriction of intramolecular rotation (RIR) in emission enhancement in a viscous solvent (glycerol) has been studied besides the vital role of intermolecular interactions scrutinized by X-ray single-crystal studies. The efficiency of intersystem crossing (ISC) in the generation of singlet oxygen (ΦΔ ∼ 19.2% and 56.7%) by photoirradiation using visible light along with distinct photostability has been investigated by 1,3-diphenylisobenzofuran (DPBF) titration studies. The 1O2 generation quantum yield and photosensitizing durability of the bis−BODIPYs have been investigated by photooxidation of 1,5-dihydroxynaphthalene (DHN) in the presence of B1 and B2 as photosensitizers. The pseudo-first-order rate constants for photooxidation reactions and consumption rates of DHN reflected appreciable 1O2 generation quantum yields (ΦΔ: B1, 29.0; B2, 57.8%). Density functional theory (DFT) studies showed the distribution of electron density over the dipyrrin moiety. Overall results indicated that these new photosensitizers (PSs) may be very promising in photodynamic therapy of tumors, photobiology, and organic photochemistry.

BODIPY-Based Multichromophoric Tripodal System as a Multifunctional Material

“…Over the course of 7 min under irradiation, tri-BDP underwent an overall 83% decrease of DPBF absorbance compared to its initial absorbance (Figure ). Based on it, the singlet oxygen ( 1 O 2 ) quantum yield (Φ Δ ) was calculated using Rose Bengal as a reference (RB, Φ Δ = 0.80 in methanol), which came out to be ∼71%. , This experiment clearly substantiated the photosensitization and singlet oxygen ( 1 O 2 ) generation ability of tri-BDP . Furthermore, it was also observed that during the course of experiment, photobleaching of tri-BDP does not occur, and thus it may be concluded that it acts as a good photosensitizer. ,, …”

“…A constant decrease in absorption at 410–415 nm (characteristic peak due to DPBF) clearly indicated 1 O 2 generation. The singlet oxygen ( 1 O 2 ) causes the oxidative degradation of DPBF, leading to a gradual decrease in the absorption at 410–415 nm. ,, Further, absorption intensity at ∼415 nm has been plotted against time intervals, which showed a linear relationship (with a slope value of 55) (Figure ). This observation suggested efficient photogeneration of 1 O 2 due to the photosensitization ability of tri-BDP .…”

“…Hence, due to the orthogonal orientation of BODIPY units in tri-BDP , it is expected that it can exhibit intersystem crossing (ISC) and generate singlet oxygen as observed in earlier reports. − Furthermore, an experiment has been performed using 1,3-diphenylisobenzofuran (DPBF) to explore the possibility of tri-BDP for intersystem crossing (ISC) and singlet oxygen generation following recent reports (Figure ). ,, As DPBF is a specific scavenger for singlet oxygen ( 1 O 2 ), it can trap the 1 O 2 produced by tri-BDP due to its photosensitization. The absorption spectra of the mixture of tri-BDP (as a photosensitizer) and DPBF (as a 1 O 2 scavenger) have been acquired at intervals of 30 s under visible light (450–700 nm) and molecular oxygen (Figure ).…”

“…To affirm its singlet oxygen generation and photooxidation ability as a model system, photooxidation of 1,5-dihydroxyl naphthalene (DHN) by tri-BDP (as a photosensitizer) has been examined under visible light irradiation (Figure ). DHN also serves as a 1 O 2 scavenger and is oxidized to 5-hydroxy-1,4-naphthaquinone (Juglone) upon reaction with 1 O 2 . , To monitor the progress of oxidation of DHN under the effect of visible light, we performed absorption study on a mixture of tri-BDP and DHN. Absorption spectra showed a gradual decrease in the characteristic peaks due to DHN at 298, 316, and 331 nm, with a concurrent increase around 375–430 nm due to juglone formation with increasing irradiation time (Figure ).…”

Visible Light-Induced Aerobic Oxidative Dehydrogenation of C–N/C–O to C=N/C=O Bonds Using Metal-Free Photocatalysts: Recent Developments

“…Other catalysts used in the photo-oxidation of 1,5-dihydroxynaphthalene to Juglone (85: R 1 = R 2 = R 5 = H, R 4 = OH) were two perylenebisimide- [60]fullerene systems dissolved in CH2Cl2/MeOH (9:1) (86a,b) (Figure 23) [183], although only the quantum yield of the transformation was reported. In addition, a mixture of two 1,7-phenanthroline based bis-BODIPYs with Cl-or SMesubstituents (87a,b) [184] and two BODIPY-carbazole derivatives (88a,b) [185] photocatalyzed the same oxidation of 1,5-dihydroxynaphthalene to Juglone (85: R 1 = R 2 = R 5 = H, R 4 = OH), only reporting the obtained quantum yield in the first case (Figure 24). Furthermore, methylene blue 1 has been employed in the photo-oxidation of different phenols and naphthols to quinones or naphthoquinones under continuous-flow conditions, obtaining good results [186].…”