Uptake of Chlorin e(6) Photosensitizer by Polystyrene-Diphenyloxazole-Poly(N-Isopropylacrylamide) Hybrid Nanosystem Studied by Electronic Excitation Energy Transfer

Polystyrene (PS)-diphenyloxazole (PPO) nanoparticles with attached cross-linked poly-N-isopropylacrylamide (PNIPAM) chains were obtained resulting in PS-PPO-PNIPAM hybrid nanosystems (NS). Fluorescence spectra of chlorin e(6) added to PS-PPO-PNIPAM hybrid NS revealed electronic excitation energy transfer (EEET) from PS matrix and encapsulated PPO to chlorin e(6). EEET efficiency increased strongly during 1 h after chlorin e(6) addition, indicating that uptake of chlorin e(6) by PNIPAM part of hybrid NS still proceeds during this time. Heating of PS-PPO-PNIPAM-chlorin e(6) NS from 21 to 39 °C results in an enhancement of EEET efficiency; this is consistent with PNIPAM conformation transition that reduces the distance between PS-PPO donors and chlorin e(6) acceptors. Meanwhile, a relatively small part of chlorin e(6) present in the solution is bound by PNIPAM; thus, further studies in this direction are necessary.