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<p>The temperature-dependent photophysical behavior of Coumarins 6 (C6), 7 (C7), and 30 (C30) was systematically investigated in non-polar alkane solvents (n-heptane, cyclohexane and n-hexadecane) across 303–343&#xa0;K. Using steady-state absorption and photoluminescence together with time-resolved fluorescence (TCSPC), we quantified emission maxima shifts, quantum yields (Φ), fluorescence lifetimes (τ) and derived first-order rate constants (<i>k</i><sub><i>f</i></sub>, <i>k</i><sub><i>nr</i></sub>) with propagated uncertainties. Small blue shifts in absorption and emission with heating indicate reduced solute–solvent stabilization. C6 in n-hexadecane showed increased radiative contribution at higher temperature, C7 exhibited high thermal robustness with minimal <i>k</i><sub><i>nr</i></sub> activation, and C30 was most sensitive to thermal activation in cyclohexane. Arrhenius analysis of ln<i>k</i><sub><i>n</i>r</sub> versus 1/T yields activation energies in the range 0.3–5.7&#xa0;kJ·mol⁻¹ (reported with standard errors). All Φ values were corrected for temperature-dependent refractive index (n(T)) and Förster–Hoffmann analysis ln<i>k</i><sub><i>nr</i></sub> vs. ln(η/T) confirms viscosity as a primary control parameter. These quantitative results clarify how solvent viscosity and molecular structure modulate LE–ICT balance and inform the design of thermally stable coumarin fluorophores for sensing and optoelectronic applications.</p>

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Temperature-Dependent Photophysical Analysis of Coumarins 6, 7 and 30 in Alkane Solvents: Role of Solvent Viscosity and Chain Length in Radiative and Non-Radiative Processes

  • 期刊论文

  • 发表日期：

    2025年12月9日

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  • Anil Kumar,
  • C. G. Renuka

摘要

The temperature-dependent photophysical behavior of Coumarins 6 (C6), 7 (C7), and 30 (C30) was systematically investigated in non-polar alkane solvents (n-heptane, cyclohexane and n-hexadecane) across 303–343 K. Using steady-state absorption and photoluminescence together with time-resolved fluorescence (TCSPC), we quantified emission maxima shifts, quantum yields (Φ), fluorescence lifetimes (τ) and derived first-order rate constants (kf, knr) with propagated uncertainties. Small blue shifts in absorption and emission with heating indicate reduced solute–solvent stabilization. C6 in n-hexadecane showed increased radiative contribution at higher temperature, C7 exhibited high thermal robustness with minimal knr activation, and C30 was most sensitive to thermal activation in cyclohexane. Arrhenius analysis of lnknr versus 1/T yields activation energies in the range 0.3–5.7 kJ·mol⁻¹ (reported with standard errors). All Φ values were corrected for temperature-dependent refractive index (n(T)) and Förster–Hoffmann analysis lnknr vs. ln(η/T) confirms viscosity as a primary control parameter. These quantitative results clarify how solvent viscosity and molecular structure modulate LE–ICT balance and inform the design of thermally stable coumarin fluorophores for sensing and optoelectronic applications.