TY - JOUR

T1 - Origin of Intersystem Crossing in Red-Light Absorbing Bodipy Derivatives: Time-Resolved Transient Optical and Electron Paramagnetic Resonance Spectral Studies with Twisted and Planar Compounds

AU - Imran, Muhammad

AU - Kurganskii, Ivan

AU - Maity, Partha

AU - Yu, Fabiao

AU - Zhao, Jianzhang

AU - Gurzadyan, Gagik G.

AU - Dick, Bernhard

AU - Mohammed, Omar F.

AU - Fedin, Matvey

N1 - J.Z. thanks the National Key Research and Development Program of China (2023YFE0197600), the NSFC (22473021 and U2001222), the Research and Innovation Team Project of Dalian University of Technology (DUT2022TB10), and the Fundamental Research Funds for the Central Universities (DUT22LAB610) for financial support. M.F. and I.K. thank the Ministry of Science and Higher Education of the Russian Federation.

PY - 2024/10/10

Y1 - 2024/10/10

N2 - We studied the intersystem crossing (ISC) property of red-light absorbing heavy atom-free dihydronaphtho[b]-fused Bodipy derivatives (with phenyl group attached at the lower rim via ethylene bridge, taking constrained geometry, i.e., BDP-1 and the half-oxidized product BDP-2) and dispiroflourene[b]-fused Bodipy (BDP-3) that have a twisted π-conjugated framework. BDP-1 and BDP-3 show strong and sharp absorption bands (i.e., ϵ = 2.0 × 105 M-1 cm-1 at 639 nm, fwhm ∼491 cm-1 for BDP-3). BDP-1 is significantly twisted (φ = 21.6°), while upon mono-oxidation, BDP-2 becomes nearly planar on the oxidized side (φ = 3.5°). Interestingly, BDP-2 showed efficient ISC (triplet state quantum yield, ΦT = 40%) due to S1/T2 state energy matching. Long-lived triplet excited state was observed (τT = 212 μs in solution and 2.4 ms in polymer matrix), and ISC takes 4.0 ns. Differently, twisted BDP-1 gives weak ISC only 5%, ISC takes 7.7 ns, and the triplet state is populated only with addition of ethyl iodide. Time-resolved electron paramagnetic resonance spectra of BDP-1 revealed the coexistence of two triplet states, with drastically different zero-field splitting D parameters of −2047 MHz and −1370 MHz, respectively, along with varying sublevel population ratios. We demonstrate that the ISC is not necessarily enhanced by torsion of the π-conjugation framework; instead, S1/Tn state energy matching is more efficient to induce ISC even in compounds that have planar molecular structures.

AB - We studied the intersystem crossing (ISC) property of red-light absorbing heavy atom-free dihydronaphtho[b]-fused Bodipy derivatives (with phenyl group attached at the lower rim via ethylene bridge, taking constrained geometry, i.e., BDP-1 and the half-oxidized product BDP-2) and dispiroflourene[b]-fused Bodipy (BDP-3) that have a twisted π-conjugated framework. BDP-1 and BDP-3 show strong and sharp absorption bands (i.e., ϵ = 2.0 × 105 M-1 cm-1 at 639 nm, fwhm ∼491 cm-1 for BDP-3). BDP-1 is significantly twisted (φ = 21.6°), while upon mono-oxidation, BDP-2 becomes nearly planar on the oxidized side (φ = 3.5°). Interestingly, BDP-2 showed efficient ISC (triplet state quantum yield, ΦT = 40%) due to S1/T2 state energy matching. Long-lived triplet excited state was observed (τT = 212 μs in solution and 2.4 ms in polymer matrix), and ISC takes 4.0 ns. Differently, twisted BDP-1 gives weak ISC only 5%, ISC takes 7.7 ns, and the triplet state is populated only with addition of ethyl iodide. Time-resolved electron paramagnetic resonance spectra of BDP-1 revealed the coexistence of two triplet states, with drastically different zero-field splitting D parameters of −2047 MHz and −1370 MHz, respectively, along with varying sublevel population ratios. We demonstrate that the ISC is not necessarily enhanced by torsion of the π-conjugation framework; instead, S1/Tn state energy matching is more efficient to induce ISC even in compounds that have planar molecular structures.

UR - https://www.scopus.com/record/display.uri?eid=2-s2.0-85205779969&origin=inward&txGid=640d929e0e486091b0c7139a6a66bff9

UR - https://www.mendeley.com/catalogue/40b95007-da84-3e50-85d0-e343a40dae63/

U2 - 10.1021/acs.jpcb.4c05418

DO - 10.1021/acs.jpcb.4c05418

M3 - Article

C2 - 39345198

VL - 128

SP - 9859

EP - 9872

JO - Journal of Physical Chemistry B

JF - Journal of Physical Chemistry B

SN - 1520-6106

IS - 40

ER -