Photophysical studies of a coumarin derivative in the aqueous solution of three different classes of copolymers

Abstract

In this article we have reported the modulation of spectral behavior of a hydrophilic coumarin based molecule 7-(diethylamino) coumarin-3-carboxylic acid (7-DCCA) in aqueous solution of polyethylene oxide (PEO)-polypropylene oxide (PPO) block copolymers with different structures and hydrophobicity. Linear triblock copolymer namely Pluronic (F-98, F-38, P-84), its X-shaped counterpart namely Tetronic (T-1304, T-1307) along with a reverse Pluronic (17-R4) were utilised with a temperature variation from 10 °C to 50°C and 7-DCCA was used as the probe to observe the changes in photophysical aspect. Of the studied copolymers, 10 wt% T-1307 and F-38 face difficulty in micelle formation owing to their hydrophilic nature and lower molecular weight PPO blocks. Also, 0.1 wt% 17-R4 remains as single-coils in the studied temperature range. Hence, these copolymers induce a different environment on the photophysics in 7-DCCA as compared to copolymers that form usual micelles (10 wt% T-1304, P-84, F-98). With increasing temperature, a persistent blue-shift in absorption and excitation spectra of the probe could be noticed upon addition of 10 wt% T-1304, T-1307, F-98, P-84, as well as 0.1 wt% 17-R4. The fluorescence emission maximum of the probe blue-shifted in T-1304, T-1307, F-98 and P-84 solutions whereas a red-shift was noticed in 17-R4. The fluorescence emission decays collected in the presence of T-1304, T-1307, F-38, F-98 and P-84 were fitted using tri-exponential functions while bi-exponential functions were used in the presence of 17-R4. A dip-rise-dip anisotropy decay pattern was observed for T-1307, F-38, and 17-R4 whereas, bi-exponential functions were used for T-1304, F-98 and P-84. The constitution of the copolymer along with its molecular properties helped us to correlate the obtained data.