Ultrafast Photoinduced Electron Transfer and Charge Stabilization in Donor–Acceptor Dyads Capable of Harvesting Near‐Infrared Light

Abstract

To harvest energy from the near-infrared (near-IR) and infrared (IR) regions of the electromagnetic spectrum, which constitutes nearly 70 % of the solar radiation, there is a great demand for near-IR and IR light-absorbing sensitizers that are capable of undergoing ultrafast photoinduced electron transfer when connected to a suitable electron acceptor. Towards achieving this goal, in the present study, we report multistep syntheses of dyads derived from structurally modified BF2-chelated azadipyrromethene (ADP; to extend absorption and emission into the near-IR region) and fullerene as electron-donor and electron-acceptor entities, respectively. The newly synthesized dyads were fully characterized based on optical absorbance, fluorescence, geometry optimization, and electrochemical studies. The established energy level diagram revealed the possibility of electron transfer either from the singlet excited near-IR sensitizer or singlet excited fullerene. Femtosecond and nanosecond transient absorption studies were performed to gather evidence of excited state electron transfer and to evaluate the kinetics of charge separation and charge recombination processes. These studies revealed the occurrence of ultrafast photoinduced electron transfer leading to charge stabilization in the dyads, and populating the triplet states of ADP, benzanulated-ADP and benzanulated thiophene-ADP in the respective dyads, and triplet state of C60 in the case of BF2 -chelated dipyrromethene derived dyad during charge recombination. The present findings reveal that these sensitizers are suitable for harvesting light energy from the near-IR region of the solar spectrum and for building fast-responding optoelectronic devices operating under near-IR radiation input.

Strongly Coupled Oxasmaragdyrin–BF2 Chelated Dipyrrin Dyads: Syntheses, X‐ray Structure, Ground‐ and Excited‐State Charge‐Transfer Interactions

“…In toluene, the instantaneously formed singlet excited 1 osm* revealed peaks at 500, 607, and 671 nm and a near‐IR peak at 1242 nm (see spectrum recorded at 1.3 ps). The near‐IR peak has been attributed to singlet–singlet transition as similar peaks are often observed for porphyrin and BODIPY compounds . In addition, negative peaks at 450, 475, 645, and 706 nm were observed.…”

Tuning Optical and Electron Donor Properties by Peripheral Thio–Aryl Substitution of Subphthalocyanine: A New Series of Donor–Acceptor Hybrids for Photoinduced Charge Separation

“…Because of the different p-conjugated skeleton, shape, and structure of SubPcf rom the commonly used porphyrins and phthalocyanines,t hese molecules show distinct optical ande lectronic properties. [54][55][56][57] Most of the phthalocyanines revealt heir intense visible-banda bsorption around6 50-700nm. [39][40][41][42][43][44][45][46][47][48][49][50][51][52] SubPcs display light absorption properties in the UV/Vis regioni nt he contexto fsolar energyc onversion.…”

“…[53] Near-IR sensitizers are especially importantf or lightenergy-harvesting applications for which sunlight carries over 50 %o fi ts radiation.G enerally,p orphyrins,p hthalocyanines, and BODIPYsh aveb een used to synthesize near-IRs ensitizers after structuralm odificationsa nd central metal-atom variations. [54][55][56][57] Most of the phthalocyanines revealt heir intense visible-banda bsorption around6 50-700nm. [35][36][37] Recently,i th as been demonstrated that by introducing phosphorus(V) into the central cavity and peripheral substitution of electron-do-nating substituents (Group 16:Sand Se), the phthalocyanine visible-band could be red-shifted beyond 1000 nm through synergistic effects.…”

Panchromatic Light Capture and Efficient Excitation Transfer Leading to Near‐IR Emission of BODIPY Oligomers

“…The 3-pyrrolyl BODIPYsh ave better photophysical properties than mesoaryl BODIPYs.P erusal of the literature revealed interesting reports on covalently linked, strongly coupledB ODIPY oligomers, [21] but reports on multi-BODIPY systems based on 3-pyrrolyl BODIPYs are scarce because of the unavailability of appropriate functionalized 3-pyrrolyl BODIPYs. In continuationo fo ur work on 3-pyrrolyl BODIPYs, [70][71][72][73][74][75][76][77][78][79] herein we report the synthesis of and studies on covalently linked BODIPYo ligomers 1-3 based on 3-pyrrolyl BODIPY.O ur aim was to preparea ppropriately functionalized 3-pyrrolyl BODIPYst hat can be used as buildingb locks to synthesize covalentlyl inked BODIPY oligomers. Thus, we prepared functionalized meso-aryl 3-pyrrolyl BODIPY 6 having af ormyl group [80,81] at the a position of the appended pyrrolyl substituent and ap rotected ethynylg roup All-BODIPY-based (BODIPY = boron-dipyrromethene) donor-acceptor systems capable of wide-band absorbance leading to efficient energy transfer in the near-IR region are reported.…”

“…Perusal of the literature revealed interesting reports on covalently linked, strongly coupled BODIPY oligomers, but reports on multi‐BODIPY systems based on 3‐pyrrolyl BODIPYs are scarce because of the unavailability of appropriate functionalized 3‐pyrrolyl BODIPYs. In continuation of our work on 3‐pyrrolyl BODIPYs, herein we report the synthesis of and studies on covalently linked BODIPY oligomers 1 – 3 based on 3‐pyrrolyl BODIPY. Our aim was to prepare appropriately functionalized 3‐pyrrolyl BODIPYs that can be used as building blocks to synthesize covalently linked BODIPY oligomers.…”