We designed and synthesized two novel molecular dyads featuring dibenzothiophene (DBT)/dibenzofuran (DBF) and pyrene (Py) moieties. The molecular design is based on the free rotation around the C–C linker to facilitate suitably rotatable configuration. Providing a systematic platform to dissect the effect of the S vs O atom on charge transfer and intersystem crossing (ISC) dynamics, which are conducive to spin-active organic chromophore systems. The interaction between DBT/DBF and Py units in the dyads is not negligible at the ground state, which is evident by redshifting the absorption spectra and exhibiting strong absorption (ε = 6.68 × 104 M−1 cm−1) compared with pristine Py moiety. The photophysics of dyads is environment-dependent: ultrafast transient absorption spectra in THF solution show the ISC occurs from singlet to triplet manifold with time constants of ∼8.8 ns for Py-DBT and ∼14.8 ns for Py-DBF, in agreement with the S1 state decay. Contrarily, in the solid matrix, the ISC is dramatically accelerated to ∼95 ps for Py-DBT vs ∼679 ps for Py-DBF. The solvent polarity of solution and heteroatom substitution significantly influenced the ISC rate and triplet state lifetime. The formation of long-lived triplet excited state is confirmed by nanosecond transient absorption spectra, and a pyrene-originated delocalization of triplet state is observed, supported by the excited triplet state spin density redistribution. Theoretical calculations support the experimental observations, showing that the efficient ISC pathways involve higher-lying triplet states (S1 → Tn, n = 3–5), driven by non-negligible spin-orbit coupling (SOC ∼0.45 cm−1) and fast ISC rate constants (kISC ∼5.7 × 107s−1). In these dyads, the ISC kinetics are dominated by the Herzberg-Teller vibronic coupling between transitions involving even similar π-π∗ electronic character states rather than Frank-Condon contributions.
Heteroatom-guided control of intersystem crossing dynamics in compact pyrene-dibenzoheterole dyads: Photophysical insights from solution and solid state studies
Mazzone G.
;
2026-01-01
Abstract
We designed and synthesized two novel molecular dyads featuring dibenzothiophene (DBT)/dibenzofuran (DBF) and pyrene (Py) moieties. The molecular design is based on the free rotation around the C–C linker to facilitate suitably rotatable configuration. Providing a systematic platform to dissect the effect of the S vs O atom on charge transfer and intersystem crossing (ISC) dynamics, which are conducive to spin-active organic chromophore systems. The interaction between DBT/DBF and Py units in the dyads is not negligible at the ground state, which is evident by redshifting the absorption spectra and exhibiting strong absorption (ε = 6.68 × 104 M−1 cm−1) compared with pristine Py moiety. The photophysics of dyads is environment-dependent: ultrafast transient absorption spectra in THF solution show the ISC occurs from singlet to triplet manifold with time constants of ∼8.8 ns for Py-DBT and ∼14.8 ns for Py-DBF, in agreement with the S1 state decay. Contrarily, in the solid matrix, the ISC is dramatically accelerated to ∼95 ps for Py-DBT vs ∼679 ps for Py-DBF. The solvent polarity of solution and heteroatom substitution significantly influenced the ISC rate and triplet state lifetime. The formation of long-lived triplet excited state is confirmed by nanosecond transient absorption spectra, and a pyrene-originated delocalization of triplet state is observed, supported by the excited triplet state spin density redistribution. Theoretical calculations support the experimental observations, showing that the efficient ISC pathways involve higher-lying triplet states (S1 → Tn, n = 3–5), driven by non-negligible spin-orbit coupling (SOC ∼0.45 cm−1) and fast ISC rate constants (kISC ∼5.7 × 107s−1). In these dyads, the ISC kinetics are dominated by the Herzberg-Teller vibronic coupling between transitions involving even similar π-π∗ electronic character states rather than Frank-Condon contributions.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
