At higher concentration due to intermolecular interaction (agglomeration) the absorption coefficient of the molecule/ aggregate might change. At what concentration you are working?  At higher concentration Lambert-Beer's plot will show non-linearity. For a equilibrium between two species (monomer and aggregation) you should also see an isobestic point. A temperature dependent study will shift the equilibrium and an isobestic point should be observed (assuming temperature itself doesn't change the absorption coefficient). You also need to independently confirm that aggregates are formed at that concentration. A DOSY NMR will help here. I would also like to see the spectra.

At higher concentration due to intermolecular interaction (agglomeration) the absorption coefficient of the molecule/ aggregate might change. At what concentration you are working?  At higher concentration Lambert-Beer's plot will show non-linearity. For a equilibrium between two species (monomer and aggregation) you should also see an isobestic point. A temperature dependent study will shift the equilibrium and an isobestic point should be observed (assuming temperature itself doesn't change the absorption coefficient). You also need to independently confirm that aggregates are formed at that concentration. A DOSY NMR will help here. I would also like to see the spectra.

as Tuhin mentioned be aware of limits of Lambert-Beer law. Make sure to limit investigations to absorbance values not much higher than 1. This can be done by using smaller path length at higher concentration.

Any change in the electrons delocalization can produce a shift in the UV-VIS spectra.

Thus aggregation could be a cause of the shift you observe.

thank you #Tuhin Khan sir, #Titus Sobisch Sir, and #Federico Svarc sir for your valuable suggestions. Probably the aggregation happening even in lower concentration and the electrons delocalization in the aromatic rings  causing the hyperchromic shift.