This document is a first stage report submitted as part of an M.Sc. project studying the preferential solvation of a hydrogen bonding fluorescent probe in alkane-alcohol mixtures using time-resolved emission spectroscopy (TRES). The report introduces the project, presents steady-state fluorescence results showing solvent-dependent spectral shifts and intensity quenching. Time-resolved fluorescence measurements reveal biexponential decays with rise times indicating translational diffusion. TRES and solvent correlation functions provide insight into solvation dynamics, with methanol causing stronger quenching than larger alcohols. Preliminary results support assigning the rise time to dipolar enrichment of the solvation shell.

1. Dynamics of Preferential Solvation of a
Hydrogen Bonding Fluorescent Probe in
Alkane-Alcohol Mixtures
M.Sc. Project
First Stage Report (3rd Semester)
CH 593
Submitted by: Sambit Sundar De
(1750300026)
Supervisor: Prof. Anindya Datta
Department of Chemistry
Indian Institute of Technology Bombay

2. INTRODUCTION
 Study of Quinolines and their derivatives
They shows photophysical property like
• Spectral property (relative energies of nπ*
and ππ* states )
• Solute with different solvents having
different spectral properties interchange of
wavelengths and decay times
• Generating TRES and study of solvent
correlation function to know details of
emitting species having different lifetimes
and overlapping spectral properties
Key points-Solvation Effect And Relaxation Process
 Solvation Dynamics- an interaction of a
solute with the solvent, which leads to
stabilization of the solute species in the
solution
 Key factors of solvation- hydrogen
bonding, ion-dipole interactions, and van der
Waals forces
 Solvent Mixture Taken- Polar and Non-
polar

3. Calculation of TRES and Solvent correlation function-
• Different wavelengths intensity decay is variable due to change of spectral properties.
• Investigate properly rise time and decay time in excited state of molecules
• Take normalized intensity decays
So, What are the main reasons behind these photophysical
property?
Phys. Chem. Chem. Phys. 2018, 20, 22320
MOTIVATION

4. To calculate normalized intensity decays, we use the
below equation-
𝐼 𝜆, 𝑡 = 𝐼𝑠𝑠
𝜆 𝑖 𝑎 𝑖 𝑒
−
𝑡
𝜏 𝑖
𝑖 𝑎 𝑖 𝜏𝑖
solvent correlation function is calculated as-
𝐶(𝑡) =
𝜈 𝑡 − 𝜈 ∞
𝜈 0 − 𝜈 ∞
 Strongly wavelength dependent decays are observed which is
indicative of multi-step excited state process taking place.
 Fluorescence lifetimes is the emergence of a nanosecond order
lifetime.
 Relationship between rise time and decay time at excited state to
assign translational diffusion time.
FOCUSING POINTS

5. • Steady State Measurements:
Two major points of observation are the gradual
and significant Stokes’ shift and the quenching of
emission intensity
Solvent λabs (nm) λabs (cm-1) λems (nm) λems (cm-1) Stokes Shift (cm-1)
Hexane 335 29850 418 23923 5927
Methanol 356 28089 520 19230 8859
t-Butyl Alcohol 349 28653 510 19607 9046
Hexanol 345 28985 508 19685 9300
Spectral properties in solvents used.
RESULTS AND DISCUSSION

6. QUENCHING OF EMISSION
Figure 1: Fluorescence spectra observed for 5AQ in hexane-alcohol solvent
mixtures with increasing amount of alcohol (%v/v) added: (a) Methanol (b)
t-Butyl alcohol and (c) Hexanol

7. Fluorescence lifetime of 5AQ in hexane-hexanol solvent
mixture measured at 420 nm and 485 nm. λexc = 336 nm.
LIFETIME MEASUREMENT

8. Fluorescence lifetime of 5AQ in hexane-hexanol solvent
mixture measured at 420 nm and 485 nm. λexc = 336 nm.
LIFETIME MEASUREMENT

9. Comparison of fluorescence decays at 485 nm for various
polar protic components used (methanol, t-butyl alcohol,
hexanol).
LIFETIME MEASUREMENT

10. Solvent τ1 a1 τ2 a2 χ2
0.1% v/v
Methanol 1.85 -0.08 7.71 1.08 1.06
t-Butyl Alcohol 2.07 -0.71 8.24 1.71 1.08
Hexanol 2.3 -0.54 8.6 1.54 1.07
0.2% v/v
Methanol 1.7 -0.77 4.36 1.77 1.07
t-Butyl Alcohol 1.78 -1.09 6.91 2.09 1.07
Hexanol 1.99 -1.32 7.91 1.32 1.11
TCSPC fitting parameters
SOLVATION DYNAMICS
Key points: Size factor, Rise time, Concentration

11. TRES GENERATE
Figure 4: Wavelength dependence of fluorescence decay profiles of 5AQ in 0.1%
(v/v) Methanol in Hexane solvent mixture recorded using λex = 375 nm and
emission monitored from λems = 390nm to λems = 520nm at 10 nm intervals

12. Figure 5: Wavelength dependence of fluorescence decay profiles of 5AQ in 0.1%
(v/v) tBuOH in Hexane solvent mixture recorded using λex = 375 nm and emission
monitored from λems = 390nm to λems = 540nm at 10 nm intervals
TRES GENERATE

13. Figure 6: Calculated TRES for 5AQ in 0.1% v/v tBuOH in Hexane at various
delay times
TRES GENERATE
Peak maxima for time zero spectrum is at 23503 cm-1 and
at infinite time the maxima is 22223 cm-1

14. Figure 7: Solvent correlation function C(t) for 5AQ in 0.1% v/v
MeOH in Hexane (blue) and 0.1% v/v tBuOH in Hexane (brown).
Solvent correlation function C(t)
𝐶(𝑡) =
𝜈 𝑡 − 𝜈 ∞
𝜈 0 − 𝜈 ∞

15.  We have systematically investigated the effect variation of alcohol
polarity and size imparts to photophysical dynamics
 Methanol causes the most drastic quenching and decreases as size
of alcohol increases
 The magnitude of rise time decreases as concentration of alcohol
in the solvent mixture increases
 Biexponential fitting C(t) for tBuOH-Hexane solvent mixture
gives decay times of 2.4 ns and 7.5 ns. The smaller component of
2.4 ns is similar to the rise time of 2.07 ns observed in simple
TCSPC decays measured at the red-end of spectra
Based on preliminary results we had assigned this rise time to
translational diffusion time of molecules from bulk for dipolar
enrichment of solvation shell. Solvent correlation function lends
credence to this hypothesis.
CONCLUSION

16. • Lakowicz, J. R. Principles of Fluorescence Spectroscopy
Principles of Fluorescence Spectroscopy 2006
• Maroncelli, M.; Fleming, G. R. J. Chem. Phys. 1987, 86
(11), 6221-6239
• Schulman, S. G.; Sanders, L. B. Anal. Chim. Acta 1971, 56
(1), 83-89.
• Bridhkoti, J. P.; Joshi, H. C.; Pant, S. J. Mol. Liq. 2011, 164,
197-200.
• Singh, A. K.; Das. S.; Karmakar, A.; Kumar, A.; Datta, A.
Phys. Chem. Chem. Phys. 2018, 20, 22320-22330.
REFERENCES

17. • I express my utmost gratitude to Prof. Anindya Datta
for his guidance and constant support throughout the
project.
• I also take this opportunity to express my sincere
regards to my senior Miss Sharmistha Das (Ph.D.
Scholar) for her continuous support.
• I am also thankful to all my lab mates and friends who
helped me to understand various concepts related to
the project.
ACKNOWLEDGEMENT