TY - JOUR

T1 - Triplet Excited State Mechanistic Study of meso-Substituted Methylthio Bodipy Derivative: Time-Resolved Optical and Electron Paramagnetic Resonance Spectral Studies

AU - Imran, Muhammad

AU - Kurganskii, Ivan

AU - Taddei, Maria

AU - Butera, Valeria

AU - Zhao, Jianzhang

AU - Fedin, Matvey V.

AU - Di Donato, Mariangela

AU - Mazzone, Gloria

N1 - J.Z. thanks the NSFC (U2001222), the State Key Laboratory of Fine Chemicals, the Research and Innovation Team Project of Dalian University of Technology (DUT2022TB10), the Fundamental Research Funds for the Central Universities (DUT22LAB610) and the Department of Education of the Xinjiang Uyghur Autonomous Region (TianShan Chair Professor) for financial support. M. F. and I. K. thank the Ministry of Science and Higher Education of the Russian Federation (Grant No. 075\u201015\u20102020\u2010779). M.D.D. and M.T. acknowledge financial support from the European Union's Horizon 2020 research and innovation program under Grant Agreement no. 871124 Laserlab\u2010Europe. G.M. thanks the Universit\u00E0 della Calabria for financial support.

PY - 2024/7

Y1 - 2024/7

N2 - Understanding the intersystem crossing (ISC) mechanism of organic compounds is essential for designing new triplet photosensitizers. Herein, we investigated the ISC mechanism of a heavy atom-free Bodipy derivative with thiomethyl substitution (S−BDP). A long-lived triplet state was observed with nanosecond transient absorption spectroscopy with lifetime of 7.5 ms in a polymer film and 178 μs intrinsic lifetime in fluid solution, much longer as compared with what was previously reported (apparent triplet lifetime=15.5 μs). Femtosecond transient absorption studies retrieved an ISC time constant of ∼3 ns. Time-resolved electron paramagnetic resonance (TREPR) indicated a special triplet electron spin polarization phase (ESP) pattern (a, e, a, e, a, e) for S−BDP, different from the ESP (e, e, e, a, a, a) typical for the spin-orbital coupling (SOC) mechanism. This indicates that the electron spin selectivity of the ISC of S−BDP is different from that of the normal SOC effect in iodo-Bodipy. Simulations of the TREPR spectra give a zero-field-splitting D parameter of −2257 MHz, much smaller as compared to the reference 2,6-diiodo-Bodipy (D=−4380 MHz). The computed SOC matrix elements (0.28–1.59 cm−1) and energy gaps for the S1/Tn states suggest that the energy matching between the S1 and T2/T3 states (supported by the largest kISC ∼109 s−1) enhances the ISC for this compound.

AB - Understanding the intersystem crossing (ISC) mechanism of organic compounds is essential for designing new triplet photosensitizers. Herein, we investigated the ISC mechanism of a heavy atom-free Bodipy derivative with thiomethyl substitution (S−BDP). A long-lived triplet state was observed with nanosecond transient absorption spectroscopy with lifetime of 7.5 ms in a polymer film and 178 μs intrinsic lifetime in fluid solution, much longer as compared with what was previously reported (apparent triplet lifetime=15.5 μs). Femtosecond transient absorption studies retrieved an ISC time constant of ∼3 ns. Time-resolved electron paramagnetic resonance (TREPR) indicated a special triplet electron spin polarization phase (ESP) pattern (a, e, a, e, a, e) for S−BDP, different from the ESP (e, e, e, a, a, a) typical for the spin-orbital coupling (SOC) mechanism. This indicates that the electron spin selectivity of the ISC of S−BDP is different from that of the normal SOC effect in iodo-Bodipy. Simulations of the TREPR spectra give a zero-field-splitting D parameter of −2257 MHz, much smaller as compared to the reference 2,6-diiodo-Bodipy (D=−4380 MHz). The computed SOC matrix elements (0.28–1.59 cm−1) and energy gaps for the S1/Tn states suggest that the energy matching between the S1 and T2/T3 states (supported by the largest kISC ∼109 s−1) enhances the ISC for this compound.

KW - BODIPY

KW - intersystem crossing

KW - photosensitizers

KW - time-resolved electron paramagnetic resonance

KW - triplet states

UR - https://www.scopus.com/record/display.uri?eid=2-s2.0-85193989779&origin=inward&txGid=5db90ccd0a4e17c35d373d2d2edb0876

UR - https://www.mendeley.com/catalogue/a5b72e57-03cd-361d-9d04-041bd2136d58/

U2 - 10.1002/cptc.202300320

DO - 10.1002/cptc.202300320

M3 - Article

VL - 8

JO - ChemPhotoChem

JF - ChemPhotoChem

SN - 2367-0932

IS - 7

M1 - e202300320

ER -