Vectorial Charge Separation and Selective Triplet-State Formation during Charge Recombination in a Pyrrolyl-Bridged BODIPY–Fullerene Dyad

Abstract

A donor-acceptor dyad comprised of BF2-chelated dipyrromethene (BDP or BODIPY) and fullerene connected with a pyrrole ring spacer, 1 has been newly synthesized and characterized. Due to -carbon substitution and extended conjugation offered by the pyrrole ring, the optical absorbance and emission spectra of BDP macrocycle was found to be red-shifted significantly.Electrochemical studies provided information on the redox potentials while computational studies performed at the B3LYP/6-31G* level yielded an optimized geometry of the dyad that was close to that reported earlier for a BDP-C60 dyad covalently connected through the central boron atom, 2. The HOMO of the dyad was found to be on the BDP macrocycle, extended over the pyrrole bridging group, a property that is expected to facilitate electronic communication between the BDP and fullerene entities. The established energy level diagram using spectral, redox and optimized structural results predicted possibility of photoinduced electron transfer in both benzonitrile and toluene, representing polar and nonpolar solvents. However, such energy diagram suggested different routes for the charge recombination processes, that is, direct relaxation of the radical ion-pair in polar solvent while populating the triplet level of the sensitizer ( 3 BDP* or 3 C60*) in nonpolar solvent. Proof for charge separation and solvent dependent charge recombination processes were established from studies involving femto-and nanosecond pump-probe spectroscopy. The measured rate of charge separation, kCS for 1 was higher in both solvents compared to the earlier reported values for 2 due to electronically well-communicating pyrrole spacer. The charge recombination in toluene populated 3 BDP* as an intermediate step while in benzonitrile it yielded directly ground state of the dyad. The present findings reveal the significance of pyrrole spacer between the donor and acceptor to facilitate charge separation and solvent polarity dependent charge recombination processes.

Efficient Radical‐Enhanced Intersystem Crossing in an NDI‐TEMPO Dyad: Photophysics, Electron Spin Polarization, and Application in Photodynamic Therapy

“…[14] As the ISC from S 1 to T n states is spin-forbidden, efficient ISC is rare for most organic chromophores with planar aromatic frameworks. Typical approaches to enhancing the ISC of organic chromophores include the heavyatom effect, [15][16][17][18][19] excitonc oupling, [20][21][22] charget ransfer, [23][24][25][26][27][28][29] use of as pin converter, [30][31][32][33] and energy-matched S 1 /T n states. [34] However,d rawbacks do exist for these conventional methods.…”

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.…”

“…Thus, a wide variety of BODIPYs have been synthesized and explored for their novel optical properties and energy‐harvesting applications . We recently reported a facile route for the synthesis of BF 2 complexes of meso ‐aryl pyrrolyldipyrrins (3‐pyrrolyl BODIPYs), which were not easily accessible before. The 3‐pyrrolyl BODIPYs have better photophysical properties than meso ‐aryl BODIPYs.…”

“…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.…”

“…Thus, aw ide variety of BODIPYs have been synthesized ande xplored for their novel optical properties and energy-harvesting applications. [57][58][59][60][61][62][63][64][65][66][67][68][69] We recently reported af acile route for the synthesis of BF 2 complexes of meso-aryl pyrrolyldipyrrins [70][71][72][73] (3-pyrrolyl BODIPYs), which were not easily accessible before. 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.…”