UV-visible and fluorescence spectroscopic assessment of meso‑tetrakis‑(4‑halophenyl) porphyrin; HTXPP (X = F, Cl, Br, I) in THF and THF-water system: Effect of pH and aggregation behaviour.

The current study determines optical and fluorescence response of halogen substituted series of meso‑tetrakis‑(4‑halophenyl) porphyrin; HTXPP (Halo = F, Cl, Br, I) dye in tetrahydrofuran; THF and THF-water system at changing pH in relationship with changing medium of allure. Effects produced by varying the pH and medium, over spectral and aggregation were discussed in detail. Results show sequential protonation and deprotonation of HTXPP series in acidic (pH = 4) and (pH =10) basic medium. Specific structural changes of monomeric absorption band were put in evidence on lowering pH, which includes broadening and splitting of soret or B band. Other changes include increasing in intensity and red-shifting of Q1 band indicating some degree of aggregation. The side-by-side aggregation and formation of J-aggregate were quite evident. The red shift of B band featured self-aggregation through head-to-tail molecular ordering which is consonant with absorption-emission data.